#0042: Creating a charging cable for a pair of Hatteker RFC-691 electric hair clippers

2026-09-19 Otto

#0042: Creating a charging cable for a pair of Hatteker RFC-691 electric hair clippers

Preamble

This article will contain a guide to creating a basic DIY replacement charging cable. This cable is for a battery powered portable pair of electric hair clippers. Brand “Hatteker”, model “RFC-691”. A simple Chinese brand cheap pair of clippers whose proprietary charger has been misplaced. In addition to the tutorial itself, I will also opine on the value of ad-hoc crafts such as this.

Technical specifications (from device label information)

Description: Battery powered portable shaver
Brand: Hatteker
Model: RFC-691
Input: 5V DC @ 1000mA
Battery: 1x Li-ion 18650 – 1200mAh
Charge time: 1.5 hours

Hatteker RFC-691 official cable examination

The cable being replaced here is a simple DC-to-DC charging cable. It has a male USB-A plug on one end, and an IEC 60320 C7 style female plug on the other. Albeit miniaturised, polarity-keyed, and proprietary. It only has 2 lines, positive and negative. Additionally it has no active electronics. Simply passing the power directly from any standard USB-A power source to the clippers. The cable’s device is rated for 5 watts. Specifically: 5 volts direct current, at a 1 ampere max current. (It is assumed that the official cable would be built to that specification.) Very straight forward, very simple.

Why make a charge cable in general?

Why make a charge cable over buying a replacement? There are several reasons. These may include: saving time, saving money, being unable to source a replacement, or simply wanting to for fun.

With regards to saving time: it may be quicker to simply make a replacement, here and now from junk. Then it is to buy another one and wait for delivery. This is whilst also having to deal with all the potential issues that could arise within that process. One may not have the luxury of waiting the time required in order to get one’s device operable again. It may need to be working ASAP.

Now with regards to saving money. There are two factors to consider here. One is: whether or not it is in the budget. If there is no money for it, then there is no money for it. Period. It doesn’t matter how small the sum. However in my case, I simply do not want to spend the £5 odd pounds that I am seeing for what essentially is a low quality random after-market cable. One that is likely to break in a few months simply from use. Not when I can either make a better one that will last, or a free one (monetarily speaking) of comparable quality that I can then replace/fix whenever it does break.

The third reason I listed is being unable to source the exact accessory for my specific make and model. This is an issue that I have encountered after a cursory search on eBay (at the time of repair in 2025). The cable that I have found supports both model RFC-690 and RFC-692. So in all likelihood it will support my RFC-691. However it doesn’t explicitly state that it supports model RFC-691. So there is a chance that I could end up wasting time and money on an incompatible cable, even if I return it. Since I will have to pay return postage.

The fourth reason stated is for fun (aaaand profit). It’s enjoyable to make things. It is even more enjoyable to make useful things. Since one will be periodically reminded of their own abilities and competency whenever they use an item that they actually made themselves. It’s human nature. It provides a Rimworld style small mood buff: “+3 mood: used self-made tool”. (Or maybe I am just talking for myself.)

2026: Do! Not Buy.

One final reason to make this cable is that this is inline with this year’s (2026) assigned theme for my personal growth and improvement. This year’s theme is: “Do! Not Buy.” This means I am trying to focus on DO-ing more things to get to my goals, rather than BUY-ing things, that give the dopamine/illusion of progression. I am trying to build up my general skill-set experience, and simultaneously save money across the board. So make make make.

Tools and materials used

Tools:

snips
helping hands (Neilsen brand 240mm soldering aid pliers)
utility knife / precision knife
multimeter (Neoteck NTK098)
lighter
power-bank (Intempo EG0289MIX)
marker pen
nylon pry tool
soldering iron (Yihua 937D)
soldering iron wool cleaner

Materials:

[2x] crocodile clip jumper cables (black and red)
USB-A (power) cable
leaded solder
rosin solder flux
assorted heat shrink

PPE:

nitrile gloves
safety glasses

Build procedure summary

insure that all relevant tools and materials are identified and within reach.
acquire donor parts: USB-A to USB-C power cable and 2 crocodile jumper cables (AKA test leads).
using snips cut off the USB plug that is not being used.
using a utility knife slice down the outer insulation of the USB-A cable to expose the inner wires.
using pry-tool: splay open and pull back the outer insulation, then pull out inner wires.
using snips nip the insulation on the inner wires ~1cm in from the end then pull it off.
twist each wire’s exposed copper strands into a tight braid.
using snips cut off one side of each of the red and black crocodile test leads.
using snips nip off around 1cm of the insulation of each test lead, and pull the insulation off.
twist each wire’s exposed copper strands into a tight braid.
plug the USB-A cable into a power-bank, and test voltage polarity of the wires using a multimeter.
slide heat-shrink onto each individual wire, and onto the crocodile pair and USB-A outer cable.
pair the crocodile clip wires (+/-) with their respective USB-A counterparts.
wind the paired wires together into a mechanical bond (western union splice).
using a soldering iron, leaded solder and solder flux – solder the western union splice.
using a pair of snips: Neaten the splice profile. Remove any excess solder blobs or wire.
cover the soldered splice with heat shrink then use lighter to tighten the shrink over the splice.
repeat with the larger cable heat shrink to add protection and support to lead.
inspect the created adaptor cable for any visual flaws.
using multimeter test the outputs on the shaver, then mark them positive and negative on the device.
using a power-bank, test the created cable by connecting it to the shaver.
assuming success: discard waste materials from the job, and stow all tools and materials used.

Build procedure write-up

Get, prepare, and test the parts.

Get a donor (known good) USB-A to USB-(irrelevant) cable. I used a random cheap power cable that came with a miscellaneous USB powered device. If you routinely buy USB powered devices, then you should have plenty of cables of this calibre on hand. As they seem to come boxed in as standard.

Cut off the irrelevant plug. Likely either a Micro-USB or USB-C plug. Then carefully slice down the outer insulation sheathing, and splay open the wires within. Unsheathe the insulation on the two wires within. If you used a data cable then they’d be more wires within. A typical USB-A to micro-USB cable contains four wires. Two power and two data wires. Typically colour coded as red (positive power), black (negative power), green and white (data +/-). Key word: typically. I recommend using a power-only cable: as they are both cheaper (to replace), and simpler to work on.

Regardless of what you have, the next step is to prep the wires and test the cable out. Splay out all the individual wires, then carefully snip the sheathing at about 1 cm down their length. Pinch this point with your finger nails and pull the insulation off. Repeat for all wires. Next use a multimeter test each wire to find the power positive and power negative. To verify the negative wire, test its continuity with the male USB-A plug’s outer metal. They are usually connected. Since this line is also typically used as a ground.

Alternatively test point the negative pin, once you have already identified the positive pin. Since it is its paired opposite. To test for positive power: plug the USB-A into a power bank, then using DC voltage mode on the multimeter test each cable until you came across something approximating +5 volts. Then do a continuity test from that wire to one of the two large edge pins within the USB-A male plug. This is the positive pin. With power positive and return identified, cut down and seal any other wires as they are not necessary.

Next prepare the crocodile clip jumper wires (or test leads as they are otherwise known). I like to use both a red and black cable to differentiate polarity. However you could alternatively just cut one test lead into 2 halves, and use both sides of it for the adaptor cable that we are making. Just have a way to mark the polarity of the otherwise identical clips. I chose to just use two differently coloured cables to save on confusion. I also have more of these cables then I need in the foreseeable future. So I had little reason to save on materials in that way. Using a pair of sharp snips, carefully nibble at each wire’s insulation at around the 1 cm from the tip of each wire. Then carefully pull the insulation off using finger nails.

Setup inline heat-shrink!

This stage is the one easiest to overlook. I even forgot about it while writing this up – skipping straight to the splice segment. I have been in situations where I soldered a splice I was proud of – only to find out that I forgot to slide in some heat-shrink prior. And now facing a situation where I will have to either cut it open and start again; or just use tape to insulate the cable. Both are bad choices. There is a third choice but it involves a specialised tool: liquid insulation. You could paint the joint with liquid insulation providing that you have it to hand.

I actually made a mistake at this stage and that was that I did not employ enough heat-shrink. I used four pieces of heat-shrink. One to directly insulate each exposed copper line (yellow), one to bind the opened insulation of the USB cable (blue), and one to cover and bind the 2 crocodile lines and the yellow splice heat-shrink (red). This setup works fine. However it would have benefited from having one more large piece to cover the whole assembly.

With regards to choosing specific sizes of heat-shrink. I recommend purchasing a kit of assorted sizes, and use whichever fits the specific diameters of your wires at the time. This is because wires (in the wild) come in a myriad of non-standard sizes. (I.e. independently variable wire conductor, and wire insulation diameters.) Keep in mind that most cheap heat-shrink, shrinks to around half its default size. So size it to be snug, but leave room to allow for bumps. Sometimes you may even have to use short segments of shrink to cover just the conductor if the insulation on that wire is too thick to both snugly cover a wire’s thin conductor and bridge its fat insulation segments. This is especially true for cheap wires which skim on copper conductors, but employ a thicker insulation to give the impression of being a larger gauge wire than they are.

After doing this, then use a larger sized, longer piece of heat-shrink to cover the whole patch. This is to provide a strong protective layer for the joint. With my piece I failed to do this, thus leaving a hole into the layers of insulation which could be a path of ingress for dirt, dust, and other contaminates. I’ll just seal it with a little tape. (Not pictured.)

Splice the wires together.

Next individually (and gently) twist all four wires exposed copper strands in a tight braid that resembles a solid core wire. Now pair up the wires. The positive end of the USB-A, with the end of the red crocodile clip wire. And negative with black crocodile.

Now twist the paired strands together using my splice of choice: the Western Union splice. This is done by making an “X” by crossing the 2 lengths of wire over each other. This should be done at a middle point for both wires. I will call the exposed copper of each wire between the intersection of the “X” and the rest of the wire the standing end, and the copper past the “X” the working end. Just like knot tying.

Carefully fold and twist one end of each wire’s working end over the other wire’s standing end. Repeat until the two wires are tightly twisted into each other. One tip, make sure that you are twisting the wires together in the same direction (counter/clockwise) as you twisted the individual wires themselves. This is so that they tighten, rather than loosen their structure when they are making the WU splice. Once the splice is complete: trim any excess that stands out. As this could cause an obstruction when applying heat-shrink. The sharp ends could also pierce holes in the heat-shrink once applied.

Solder the splice.

Now that there is a strong mechanical (or physical) bond (or knot) connecting the two pairs of wires together. It is time to solder the connection. Making it permanent. When soldering I typically start by warming up and cleaning the iron. This is done by applying leaded solder and repeatedly dipping the iron into a metal mesh cleaner. Do this until all dark oxidation is removed, and the iron wicks solder readily. You could also apply rosin flux in this process to aid it. I personally just dip the hot iron into the flux dish as I go.

I mention this because in my opinion when it comes to soldering: preparation is of paramount importance to the successful execution of the task. Especially when using bog standard or subpar tools. As you can not rely on a tool of this quality to work readily despite poor conditions.

The actual soldering is easy enough. Apply flux to the wire joint. Then apply a little solder to the iron, enough that it adheres to iron without forming an unwieldy blob. Now line up a section of leaded solder wire to the joint. Then run the iron across the (fluxed) joint, while feeding the solder wire into the iron; and letting it melt and run into the wires of the WU splice.

Be careful to manage the heat that is put into the splice. Too little heat and the solder won’t take to the splice, too much heat and the insulation at either end of the splice will burn, melt, and curl back. Exposing more wire than desired. Perhaps more than the prepared heat-shrink could even cover. I have even had heat shrink that was placed too close to the joint shrink on me in situ. Before being positioned. So be cognisant of how much heat is actually put into the wires.

Now. Once the soldering is completed go over it with a pair of snips to remove any bumps, excessive solder blobs, or wire ends that the solder adhered to and exaggerated its profile.

Apply the prepared heat-shrink.

Heat shrink should already be present on the wire at this stage. Slide it over the exposed segments then apply heat to activate it. Start with the smallest diameter segments to cover the exposed conductors, then move on to applying the larger bands that tidy and seal off the wires. Be careful not to accidentally apply any heat to heat-shrink that is not in place yet. As it will tighten and lock into place where ever it currently is. I used a simple disposable lighter for this. Alternatively you could use a heat gun or hot air rework station if you have one to hand. I KISS-ed this simple job. There was no need for anything more.

Testing the hair clipper.

Before we go on. We need to gauge the status of the hair clipper. Specifically I needed to know the polarity of its two pins. To do this, just apply a multimeter across its pins. Set in an appropriate DC mode. Note the read out, then swap the probes with each other and test the pins again. Note this result.

If the result is positive. It means that the positive probe is on the positive pin; and if the result is negative, then it means that the negative probe is on the positive pin. Once the positive and negative pins have been identified: mark them on the device. This is to prevent accidentally reverse charging the clipper. Which risks damaging it, and/or the charging circuitry. (Powerbank, PSU, USB wall outlet, etcetera.)

Cable test.

Test the finished cable. This involves a visual inspection. Does it look good? Fit for purpose? Is there anything notably broken on it? If it looks good; then perform a handling test. Pick it up, handle it roughly like you are actually using it without taking mindful tender care of it. Does it hold up to rough handling well? Or does it crack and fall apart? Better it breaks now, than in the moment when you need it.

Providing it passes (reasonable) rough handling. It is now time for an electrical test. I chose to use a powerbank as a power source. This is because it creates an isolated system. And limits any damage caused by short-circuits etcetera to just the created cable, clippers, and powerbank. Use a multimeter to verify polarity and electrical continuity.

Final test.

With everything else worked out. Now is the time to plug it all in and see if the cable actually charges the hair clippers. Providing that the product passes this final testing. Then it is done. If it charges as expected from the power bank, then enough confidence in the cable is present for it to be plugged into a wall charger, to charge the clippers properly. Observe the first charge cycle for signs of heat build up, shorts, or any malfunctions. Otherwise: job done.

Acronyms used

AKA – Also Known As
ASAP – As Soon As Possible
CM – Centimetre
DC – Direct Current
DIY – Do It Yourself
IIRC – If I Remember Correctly
KISS – Keep It Simple Stupid
PSU – Power Supply Unit
USB-A/C – Universal Serial Bus (A type / C type)
WU – Western Union

Closing thoughts

A brief note on time. This little project was actually completed in June of 2025. This article is one of many that have been sitting in stasis for an extended time. It feels like I only did this a couple of months ago, however to my surprise, and according to the picture file names: they were taken in 2025-06. Only recently (2026-09) did I wrap up this article and make it publishable. This “wrap up”, included additional content that makes it relevant to 2026. Such as the incorporation of this year’s theme. Forgive me this deception.

With that out of the way, there is not much to say about this article or project that I haven’t already covered above. So let’s go for a more personal note. This cable was made out of junk I had on hand, and with a time limit. A family member lost the charger for the hair clippers and needed to trim their hair by Monday, it was the weekend IIRC. The point is that there was a time limit preventing the sourcing of a ready replacement. This is the perfect scenario where an electronics hobbyist should come in clutch with a DIY cable or what-have-you. (Akshully. This cable was made shortly after this time limit, I remember just charging the clippers using a bench PSU for an hour or two. But that is a less compelling story… Apocryphal story telling == More deception!)

The point is that these types of situations will emerge, they will come suddenly with little/no notice, and usually at an inconvenient time. So it pays to become accustomed to doing this type of work at the drop of a hat, and using whatever you happen to have on hand at the time. Such is the way of things. Keep in mind that a bodged solution is still a solution. Even if it only lasts as long as it takes to source a better quality replacement. As as long as it solves the problem in the moment it arises. Buying time in process. Then it is a success.

That being said the cable I created here is of decent quality, and will last as long as it is not abused, or misused. The only issue with it is that it doesn’t have the idiot-proofing; protecting the device from user error – that the original cable had. Due to the plug’s polarity keying preventing it from being inserted backwards. That’s my final point here, be cognisant of your creations’ weaknesses. And inform the user(s) of them, while also disclaiming any damages that may be caused by using the ad-hoc component that you provided. This is key to maintaining good customer relationships. From experience it often pays to overstate the risk. This is because it causes them to take active responsibility for employing it.

In the cable’s defence, as of 2026-09 I have noticed that it is still employed by my family member. More than a year after its creation. This is a genuine credit to its quality since they evidentially haven’t felt a need to replace it in the interim. How’s that for (real-world) feedback. 😀

Thank you for reading.

#0037: Tip for securing a cabled USB type-A plug and socket together

2023-02-262025-08-14 Otto

#0037: Tip for securing a cabled USB type-A plug and socket together

Preamble

This is a quick budget tip for securing a cabled USB type-A male and female plug and socket together. This technique could probably be extrapolated for use with other plug types. However I have yet to do so.

Tip for securing a USB type-A male and female plug and socket together

Now onto the tip. Simply put, I use an elastic band to hook the two plugs together. That’s it. Done. Thank you for reading…

Still here? Okay, now onto the part where we explore in excessive detail such a simple concept. One so simple you probably have immediately intuited the basic theory of operation. If not then here it is. Basically, the elastic band applies a pulling pressure that keeps the plug and socket engaged. This is especially useful when you have an otherwise loose connection, typically caused by issues such as weak retention springs within the female socket. Something that seems common to USB extension cables in my opinion. At least the ones I have encountered.

Method of application

I like to start by using a basic cow hitch to lasso one of the plugs. This is done by folding the band into a loop and simply inserting a plug into this loop. Then tightening it around the plug’s plastic shoulders. That’s a basic cow hitch.

Now, with the other side of the elastic band wind it around the plastic shoulders of the second plug a couple of times until the elastic is reasonably taught. Then insert the male into the female plug. And done. The band should now exert force that will keep pulling them together.

Elastic band application demonstration video

Best practices

For best results, I recommend using a reasonably strong elastic band. I also recommend only wrapping it around the plug’s plastic enclosure itself, and not involving their respective cables. This is so that no force is applied to the cables themselves. Force which may aid in the development of faults such as repetitive flex damage, or a kink in the cable. Additionally when the band is secured on the plug body it focuses and directionalises the force in a way that better pulls the cable ends together.

An attentive reader may notice that in one of my example images, the one with the beige elastic. The upper band loop is a little bit too high up, and sits on the plastic wire strain relief itself, rather than the plastic plug body. What can I say? Do as I say, not as I do. 😉 Its really not a huge deal either way. Securing the loop on the plug body is just what I consider best practice.

Why not use adhesive tape instead?

Alternatively to using elastic bands, you may think: why not use tape to adhere the two ends together? Briefly put, tape is messy – it leaves glue residue when removed, it’s too permanent or hard to remove, and probably most importantly: it doesn’t put pressure on the plugs to keep them together. So as time passes the plug could slowly but steadily slip out of it’s respective socket. Due to things like vibration, gravity, or general handling.

Closing thoughts and my use-case summary

In my particular use-case, I use elastic bands like these to keep the USB extension cables attached to my 4 Watt USB lights and their switches. The weak retention springs within the female USB sockets on the extension cables allow any plugs inserted into them to eventually slip out.

I used to use electrical tape to manage this but, as time went on the tape lost it’s adherence. Yet left a mess of melted glue residue. After this I switched to using duct tape, but it was too strong, and too difficult to easily remove when I wanted to. Hence the bands. Third time the charm it seems.

So far, just common garden variety elastic bands seem to work best for me in this application. Whatever you can find is fine. Funny thing is, I didn’t even buy them. I just collected the ones that my mail man keeps dropping around my door.

All in all. This is an example of a zero budget application of junk that has gained value via use. At least I found it to be so. Anyway, I hope this article is of use to you. At the very least I hope I can raise a little awareness of the genuine potential uses of random household miscellanea. And that it may assist you in exploring alternative DIY solutions to purchasing one’s way out of any given problem. I know I have been guilty of that.

Thank you for reading.

#0010: Device analysis of a USB resistive load

2020-11-302025-08-14 Otto

#0010: Device analysis of a USB resistive load

Preamble

This will (hopefully) be a start to a series where I take a look into various devices and analyse them. My intention is to begin with very simple devices and steadily ramp up to more complicated ones as time goes on. The idea is to give the reader enough information about the device (design, function, components, etc) to the point that they can conceivably create their own. As well as in some cases recommending certain modifications, tools, adapters, or companion devices for optimal practical use.

Device information

This is a resistive load with a male USB plug interface. It’s intended function is for testing the current output of USB power-supplies and power banks. It has 2 current draw settings, these include: a 1 ampere and a 2 ampere mode. This device is operated using a two state slide-toggle switch, which allows alternating between the two current draw modes. Additionally it uses a common anode bi-colour LED as an indicator for these modes. Green for the 1 amp and red for the 2 amp mode.

The general layout and configuration of the 5 ohm wire-wound power resistors is what makes this device function. One resistor (R1) is always in circuit, in both the 1A and 2A mode. Within the 2A mode, R2 is added (in parallel to R1) to the circuit. Adding R2 in parallel to R1 reduces the circuit resistance to 2.5 ohms, which in turn draws 2 amps from the power supply.

1A mode: R1 in circuit (5V/5R=1A)
2A mode: R1 and R2 in parallel (5V/2.5R=2A)

Schematic

made using https://www.digikey.com/schemeit/

Key

R1: 5 ohm wire-wound power resistor
R2: 5 ohm wire-wound power resistor
R3: 560 ohm resistor
L1: light emitting diode (green)
L2: light emitting diode (red)
S1: toggle slide switch

Recommended modifications

3-state switch or additional switch (for device OFF state)
Heatsink / fan (to efficiently dissipate generated heat)
PTC resistor (as a safety temperature cut off)
male USB to female USB extension cable (for allowing easier multimeter access)

Additional switch

Due to both states of the USB resistive load’s two-state slide-toggle switch being used during the operation of the device, the device has no plugged-in OFF state. This means that it should not be left unsupervised whilst plugged into a power-supply as it would be active at either switch state. Either adding an additional two-state switch or replacing the current one with a three state-switch, will allow the device to have an OFF state. Whether or not this is considered valuable, is largely subjective. However personally, I like the option of turning a load off without necessarily having to unplug it.

Heatsink and fan

The reason why leaving this resistive load active and unsupervised is a concern; is predominantly due to the functioning of the two large 5 ohm power resistors. These resistors dissipate around 5 watts each (5V*1A=5W) and generate considerable heat as a result. Because of this, I recommend the addition of an appropriate heatsink to be attached to these resistors in order to dissipate this resultant heat. As it is now, during continuous operation the resistors heat up to the point that they can not be handled with a naked hand. This level of heat could pose a possible burn risk, or fire hazard.

The addition of a heatsink will allow the device to run continuously without reaching these same high temperatures, it does this by dissipating the heat generated within the resistors in a more effective manner. I.e. moving it into the environment quicker, so that it doesn’t concentrate within the device. An addition of a mounted 5 volt mini fan will enable the cooler ambient air to run through the fins of the heatsink and further improve it’s ability to move heat out of the device. I specify a 5 volts fan because it can be powered from the device itself.

In addition to allowing the device to be handled after extended periods of operation, a good heatsink will in all likelihood also extend the lifespan of the two 5 ohm power resistors. It does this by dissipating any generated heat before it reaches levels that may damage either the components themselves or their neighbours. Generally speaking: devices that run cooler, live for longer.

PTC thermistor

As an alternative to the above two fairly common sense modifications; one could also choose to incorporate a Positive Temperature Coefficient (PTC) thermistor as some kind of safety shut off in the cases where the device reaches any critically high temperatures during operation; essentially as a reusable temperature fuse. The reason why I am dubious in recommending this is that: although it will make the device safer to use in a continuous application; attaching a PTC thermistor in series with the two power resistors may actually affect the resistive load’s performance if not it’s ability to function entirely. I am not sure as I am inexperienced with the application of thermistors in general, and have yet to try this particular use-case out.

My working theory is that since a PTC thermistor increases resistance as it heats up, and with this device’s current draws; it will quickly lead to a positive feedback loop where it’s resistance generates heat, which will generate more resistance, and so on until no current can pass through it – essentially becoming open circuit. I believe that the heat generated from the low resistance power resistors will kick start that sequence; and that the increasing circuit resistance from the PTC thermistor will quickly negate the the power resistors’ ability to draw current. Even if the thermistor’s resistance doesn’t increase to the point of open circuit. It only needs to be consistently higher than the power resistors’ 5 ohms in order to hamper device functionality.

Still, perhaps there is a configuration where the PTC resistor will not negatively affect the power resistors, while still being functional as a thermal fuse. Perhaps if the trip temperature of the thermistor was high enough, or it had a position on the device where it only heated up in cases of catastrophic environmental temperatures. Basically a setup that allowed for the added safety of having a thermistor in circuit without it negatively affecting the functionality of the device.

USB extension cable

I decided to create my own USB extension cable rather than use a prebuilt one. The main reason for this is that I fear that a random off the shelf unit my not be designed to handle current draws of 2 amperes (even if it’s vendor says that it is). This would mean that the cable itself would provide a level of resistance that would become a limiter to the amount of current that the resistive load can draw.

Generally if a USB cable is offering resistance, it will be in it’s cable and not in it’s plug and socket. Either the cable itself is too thin of a gauge, made of inferior materials (aluminium instead of copper), or is long enough to cause voltage drops at higher currents. With this in mind, I used thick gauge copper power cables (taken from an extension cord), and a salvaged USB plug and socket. I also made sure to keep the total length of the cable short; just being long enough to allow comfortable use of a clamp style multimeter.

Which actually brings me to the purpose of this little extension. The pictured USB extension cable is designed to allow the use of a clamp multimeter (one that can measure DC current). Alternatively, if I didn’t have a clamp multimeter, I would cut the 5 volt line in half and terminate it’s two ends with banana plugs. That way I can insert a regular multimeter in series within the circuit; and measure the actual current draws.

As an alternative to using a DIY USB extension and a multimeter, one could just buy a USB voltmeter/ammeter. Such as the one pictured. Although these things, in my opinion can skew the results: due to them (in my experience) imparting some level of resistance on the circuit; they are certainly more convenient to use. Which one a person prioritises: accuracy, or speed (neatness, etc.) will largely depend on their preferences and use-cases.

Closing statements

Although the build quality of this device is more than acceptable (i.e. it doesn’t feel like a shoddy product), it is clearly built to a price point. Only having near enough the absolute necessary components to function. I believe this to be the case, not just because of the miniscule bill of materials (BOM), or the use of inexpensive components in that list. But rather because of the in my opinion necessary things that were left out; namely a basic heatsink.

Although it actually functions fine as is; at least for short operations. If you wish to use this device safely continuously for longer periods of time than a couple of minutes, modifications will need to be made.

Sources, references, further reading

https://en.wikipedia.org/wiki/Thermistor#PTC

https://sciencing.com/difference-between-resistive-inductive-loads-12181159.html

#0009: Brief guide to creating a USB OTG cable

2020-11-222025-08-14 Otto

#0009: Brief guide to creating a USB OTG cable

What is a USB OTG cable?

USB “OTG” stands for USB “On The Go”. USB On-The-Go is a specification of the USB protocol that allows traditionally slave devices such as smart phones, to act as master devices or host systems (e.g. personal computers) when connected to either other slave devices such as digital cameras and printers; or peripherals such: USB storage disks or human interface devices (e.g. keyboard and mouse).

USB plug classifications.

There are a myriad different types and generations of USB cables available on the market today. However most obey the convention of having two different plug-socket configuration in each class specification. A type-A plug and socket for connecting with the host system (a.k.a. “A” device), and a type-B plug and socket for connecting with the slave (or “B”) device. A standard USB cable will have one male type-A plug and one male type-B plug. A USB OTG cable differs from a standard USB cable in only one significant way. The standard USB type-A plug is replaced with either a USB Mini type-A or USB Micro type-A variant. That’s it.

For example to connect a generic modern printer to a smart phone with a USB Micro type-AB socket. One would need a male USB Micro type-A to male USB type-B cable. The replacement of the USB type-A with a USB Micro type-A is what makes it an “On The Go” configuration. This means you don’t need a traditional PC to use the printer. You can connect directly with and use the mobile device to send the files to the printer in it’s stead.

Diagram of USB 2.0 connectors. Depicting USB, USB Mini, and USB Micro type-A and type-B plugs — image taken from wikipedia.org

Limitations of the USB OTG specification.

A device with OTG enabled capabilities unfortunately can not act as a general purposes host system with the same peripheral compatibilities as a personal computer. Instead they are given a Targeted Peripheral List (TPL) from their manufacturers. This is a rather limited list of general peripherals designed to work with the particular device for it’s expected use cases. This is because these devices will have limitations on them such as power output or limited supported protocols.

Unfortunately, as I see it; with the innumerable amounts of devices (smart phones, tablets, etcetera) and peripherals (with various protocols and power draws) on the market today: the best way to find out whether or not a peripheral is compatible with your particular device – is to just plug it in and see. This is also true for finding out whether or not your device supports the USB OTG functionality in general. Some might not.

I tested a couple of smart phones I had on hand, and of the four I had, only one actually supported OTG functionality. The other three simply didn’t register the peripherals (including a basic USB thumb stick) plugged into them. These were: (2011) Samsung GT-I5500, (2012) HTC Chacha, (2015) Huawei GRA-L09, and (2018) Blackview A30. Of them only the Huawei GRA-L09 worked with my OTG cable. It performed perfectly with the wireless USB keyboard-mouse combo, and the thumb drive I tested with. The Huawei even allowed connections to the other smartphones (using a Micro type-A to Micro type-B cable). It could charge the other devices, register on their end as connected to a host, but not allow access to their filesystem like a PC would allow. This last thing could be a software limitation, that will require some further tinkering to work; or possibly using some kind of third-party file browser or peripheral manager. Long story short, when it comes to compatibility: your mileage may vary.

Creating a USB Micro OTG cable.

The USB OTG specification was originally created for use with mobile devices that utilised the USB Mini standard, and later updated to include the USB Micro standard. We will create an OTG cable by modifying a Micro type-B plug to a Micro type-A plug. Then using it to create a male USB Micro type-A to USB (full size) type-A socket. This is to connect basic low power USB peripherals such as storage drives or a wireless mouse and keyboard combo. Which is my particular use case. However it should be stated that the same modifications can be made to a USB Mini type-B plug to turn it into an OTG enabled Mini type-A plug.

To create a basic USB Micro OTG cable is actually rather simple. All you essentially need to do is short the ID pin (pin 4) on the USB Micro type-B plug to ground (pin 5). This procedure effectively (i.e. electrically) turns the Micro type-B plug into a Micro type-A plug.

Unfortunately in my case, my kit USB Micro plugs only came with 4 soldering pads (for the power and data lines). It was missing a solder pad for the ID pin. This meant I couldn’t just run a small jumper from the ID pad to the ground pad. I instead had to access the ID pin directly. On one hand this makes creating the OTG cables that require some resistance value between the ID and the ground pin significantly harder. Due to no room for the resistor. However if you intend to just create a basic cable, then this method of just bridging the ID and ground pin can be useful for salvaged USB Micro plugs who in all likelihood won’t have an ID solder pad.

With this in mind, I disassembled a kit USB Micro type-B plug. Next I scraped the covering plastic on pin 4 and 5, then soldered a bridge across them. I removed the plastic to create space and headroom for the solder bridge. Otherwise, I may be unable to slide the plug head (with it’s plastic inner lining) back on. Space constraints need to be paid attention to. Reassembled the plug. Then tested for continuity using a multimeter and a USB Micro type-B socket breakout board. Id est making sure that pin 4 is grounded, and that the solder bridge wasn’t coming off.

Please note, there are other methods for creating OTG cables that involve running a specific resistor across the ID and ground pins for certain devices to work, or to enable the host and/or peripheral device to draw power from an external power source. However I am omitting them, for brevity. This is a quick guide to build a basic DIY OTG cable.

I decided to make the pictured OTG cable modular using breadboard jumper cables. The reason for this is because I intend to mix and match various plug and socket ends to create different types of cables. However, I would recommend making a more fixed and permanent cable for actual real-world use.

Modular OTG cable example

Tooling and material example

Disassembly and modification of a USB Micro type-B plug

Modular male Micro type-A to female USB type-A OTG cable in use

Modular male Micro type-A to male Micro type-B OTG cable in use

References / Sources / Further Reading:

https://en.wikibooks.org/wiki/Serial_Programming/USB#What_is_USB?
https://en.wikipedia.org/wiki/USBhttps://en.wikipedia.org/wiki/USB_hardware
https://en.wikipedia.org/wiki/USB_On-The-Go
https://en.wikipedia.org/wiki/USB_(Communications)#Signaling_state

#0008: Repair and Analysis of USB Micro type-B cables

2020-11-062025-08-14 Otto

#0008: Repair and Analysis of USB Micro type-B cables

If you are anything like me you probably have a sizeable collection of broken Micro USB cables neatly spooled onto a hook, or into a bag. Alternatively, you may even have them tangled into a rat king in a box or drawer somewhere … that is if you are a barbarian. You know who you are. So in an effort to lighten my ‘Spares & Repairs’ bin short of throwing things away (perish the thought!). I though it’d be good to repair a few. I know crazy right?

How and where do Micro USB cables typically break?

In order to repair something, we must first asses the damage. Where is it and how much is there? Well, with regards to the generic male USB 2.0 type-A plug to male USB Micro type-B plug cable: the damage is predominantly focused in the male Micro USB plug. Please note I will be using the term ‘Micro USB plug’ as shorthand for ‘male USB Micro type-B plug’ throughout this article.

Initially, I used to get annoyed whenever a cable broke and rebuke the relatively delicate Micro USB plug as poorly designed. However, on reflection it is actually rather good that the weakest point in the pairing of the plug and socket: is in the plug and not the socket. Especially since after such incidents, the device socket tends to end up with little if no damage at all.

This is assuming that the majority of accidental breakages happen under certain conditions. These include: firstly, that the Micro USB plug is inserted into it’s respective socket on the device at the time. Whereupon it comes into acute mechanical stress by something akin a sudden impact (e.g. from a fall); or by a particularly vicious cable snag. This stress consequentially puts a lot of pressure on the connection between cable and device. Which in most cases causes the cable’s plug to give in before the device’s socket. Sometimes both are damaged if the impact is strong enough. However in a more typical scenario the plug breaks first, and in such a way as to leave the socket relatively unharmed.

Although my knee-jerk reaction is irritation whenever I perceive something as genuinely designed to break; I think in hindsight it is better that the cable’s plug is designed to break before the device’s socket. Since the cable is far easier (and consequently cheaper) to either replace or repair than the device would be. After doing some research, it seems that this is a conscious design decision (citation needed) and not one based on anti-consumer avarice, which (as a long time purchaser of consumer grade electronics) is the assumption that I have been conditioned to have in these types of scenarios. “Think Different”, Think Planned Obsolescence.

In this case, it is actually an iterative improvement on it’s predecessor: the Mini USB standard. Which suffered from port damage due to the shape and structural strength of the male plug, coupled with the fact that the retention and locking mechanism is located within the socket in the Mini USB standard. Whereas within the Micro USB standard, all such fragile and consequently breakable parts are located cable side. Having said that though, it still sucks when useful tools break so let’s try fixing them.

picture of a USB Mini socket. It shows the retention clips within the socket. — USB Mini socket

Structure of a male USB Micro type-B to male USB 2.0 type-A cable.

The male USB Micro type-B (or Micro USB) plug on average has typically four or five pads at it’s cable side and five interface pins that mate with it’s counterpart female socket. Please refer to the pin out diagram.

diagram depicting the wiring and pinout of a male USB 2.0 type-A to male USB Micro type B cable.

Its simple really, pins 1 and 5 are used for power. Pin 1 supplies the +5 volts and pin 5 is it’s ground. Pins 2 and 3 are used for transmitting the data signals for communication. And finally, pin 4 is an identification pin, which is used for USB ‘On The Go’ functionality. It essentially tells the device that it is connected to, whether or not it is to act as a host system or a slave device when communicating with the device on the other end of the cable.

hyperlink: post_#0009:_Brief_guide_to_creating_a_USB_OTG_cable

Its a very similar setup with the male USB 2.0 type-A plug on the other side of this cable, except that it lacks an ID pin. Pin 1 is the V bus carrying +5 volts, pin 4 is the signal ground, and pins 2 and 3 are the negative and positive data pins respectively.

The reason the USB type-A plug lacks an ID pin is because any device that has a full sized female USB type-A port is already assumed to be the host system. Finding a peripheral device such as a keyboard (with the exception of USB pass-through), or mouse, or even a smart phone with a full sized female USB type-A socket is non-standard; as are the male USB type-A to male USB type-A cables needed for them.

The wikipedia.org article (“USB hardware”) mentioning this cable labels it as ‘proprietary, hazardous’. If I were to guess as to why that is, I’d say its because it allows the connection of two host systems (e.g. 2 personal computers), with no protocol to decide the role either system has to play. Additionally the input of power into a host system via it’s USB ports may cause damage (e.g. to it’s USB controller) because it may lack short circuit or input protection.

The Repair

Now that we have a basic understanding of the structure of the Micro USB plug and where the damage typically is. We can proceed to repair one.

Recommended tooling:

soldering iron
hot air station / heat-gun / lighter
hot-glue gun
precision knife
third hand clamps (handy grips, etc.)
testing adapters
female USB type-A socket breakout board
female micro USB type-B socket breakout board
multimeter
pliers

Consumables:

hot-glue
heat-shrink
Micro USB male plug kit
(lead-free or leaded) solder
rosin flux
electrical tape

P.P.E.:

safety glasses
light heat resistant gloves

The list above is just as a guide the the types of tools and consumables that you may need. Most of them are optional and are subject to personal preferences and circumstance.

Methods of repairing items

Most real world cable repairs I think broadly fall into one of the three categories or ‘methods’ I outline below. They all have advantages and disadvantages. Some allow for saving more time than money and other’s vice versa. Which ones are most appropriate to use will predominantly be based on the repair technician’s personal preference, available materials, and circumstances.

For example one could if one had two good candidate cables, splice them together into a working unit (i.e. method #1) using minimal tooling: just a knife to strip the wires, several unsoldered pig tail splices for the connections, and some electrical tape to isolate the USB wires from each other. And it would work fine. How long for? Who knows – but it will work for the moment and that may actually be enough. I give the example just to illustrate that things can be repaired a number of ways depending on either the person’s (in this case low) resources, and preferences; which can the run the gambit from the “just get it working for now” repair (shown above), to the perfectionist who wants a permanent repair that will outlast the product.

Method #1: splice two cables together

Probably the quickest method of repair involves simply splicing together two cables. This involves cutting the damaged parts off, then joining and soldering the four pairs of wires together according to their colouring. Red and red, green and green, white and white, black and black; and even sometimes the foil metal shielding if present. Simple. However, be mindful to first electrically isolate each of the four individual pairs, then cover over with a larger gauge heat shrink (for neatness) or electrical tape (for cheapness) to group everything together. I recommend a soldered Western Union splice as a method of joining the wires in the pairings. This is due to it’s relatively low profile and due to the mechanical strength of the resulting connection. Which means that in the case of any future tension on the cable such a sudden hard snag; chances are good that the new connection will not break. Nothing hurts my pride quite like having to repair one of my prior repairs. Consequently, I tend to do it properly the first time round.

hyperlink: post_#0003_Basic_techniques_for_connecting_wires

Now, there are obvious limitations to this method. The most pressing is that cables tend to get damaged in the same spot as each other. Especially when used in the same environment (or by the same people!), and in the same applications. So this method is not applicable in these cases. However in cases where it is applicable it is the shortest and easiest route to creating a reliable and viable cable. Primarily because it effectively bypasses the often finicky business of repairing the actual Micro USB plug.

Method #2: mend and make do (with salvaged spares)

So, like I mentioned above: most of these cables break at the same point. Namely, the male Micro USB plug. So unless you want to end up with a bunch of double ended (full size) male USB type-A cables. Splicing together the good ends of your broken cables isn’t going to do you much good.

So what now? Well first things first. We need to understand the extent of the damage itself. When you examine a broken Micro USB plug. If the metal outer shielding of the plug is present, then chances are that the metal plug itself is bent out of alignment by a fair few degrees across it’s broader sides. In this configuration, the state of the plug’s internal pins is unknown; or more to the point: it is unknown as to whether there is continuity across the pins (i.e. are they snapped or broken). By using a pair of pliers you can carefully correct the angle of the plug. I recommend doing this slowly before trying any other fixes. It needs to be slow, in order to give the delicate internal pins time to bend back into alignment. If the cable works after this, then that means that the internal pins were merely bent and not broken; and it also means that the repair is effectively done.

Alternatively, if after angle correction there is no continuity across the cable. Either by buzzing it out using various adapters and a multimeter — or just by plugging it into (hopefully inexpensive) devices and seeing if the devices recognise each other. Then it is time for a more invasive solution. I stipulate ‘inexpensive’ because many devices with USB ports don’t have adequate protection in cases of hard shorts to ground. It’d be pretty disheartening if a person, for example killed that USB 3.0 port on a their wiz bang gaming rig, because the wires were accidentally soldered incorrectly or shorted on that cheap shit cable they were trying to mend. I doubt that would actually happen, but better safe than sorry.

With a sharp knife, slice into the rubber or plastic sides of the plug. Create a broad slice from where the metal Micro USB plug’s base is (or was), all the way across the plug housing and up close to the strain relief. Peel back the rubber or carefully pry open the plastic to reveal the base of the Micro USB plug. Here you should be able to see where the four wires (for a data cable) or two wires (for a power cable) connect to the Micro USB plug’s base internal section.

This area of the cable: where cable meets Micro USB plug; tends to be either injection moulded with plastic or rubber, or filled with a type of hot glue. It is very easy to do more damage to the plug trying to get to it, then the damage that caused the cable to become inoperable in the first place. So if you intend to repair the Micro USB plug (rather than replace it), I advise proceeding with caution here.

Once you have made it to the base of the Micro USB plug. You many notice that the metal outer shield of the Micro USB is sometimes removable. If yours is, then it should be held in by a clip of some sort. Unclip it. Continue carefully dissembling the plug until you find the fault. In my case the internal pins broke as the plug was bent. I could try to re-solder them together or I could replace the Micro USB base with one from either another plug or a spares kit. Since this is the ‘mend and make do’ method, let’s say I went through the tedium of realigning the tiny pins and soldering them – and without melting their plastic housing or shorting them together no less … What I actually did was just replace the plug base with a known good one, for time and reliability.

Reassemble the plug. Then fill in any cavities you may have carved out on your way in, with hot glue. Close the cable head up, then wrap it in electrical tape. Done.

The strength of this method is that you can repair the cable without necessarily having to purchase additional parts. However the disadvantages are that it is very time consuming and finicky work. Work that could ultimately leave you with a plug that is structurally even weaker than the one you started with. So it may soon break again if not handled with care going forwards.

Make sure to do a through continuity test before pressing this cable back into service. Especially when it comes to testing for shorts across the pins. This includes pin 4, which depending on the testing adapter socket you are using, might be inaccessible. In this case I used to use crocodile-clip leads and needles as probes to test the pins on the exposed male plug without a female adapter. Although, I actually recommend just purchasing (or creating) a female Micro USB socket breakout board. It makes life so much easier than faffing about with a bunch of random low quality adapters or needles … which is what I used to do, and don’t really recommend. But sometimes you have to just use the tools in front of you.

Method #3: use a spares kit

This is probably the simplest actual repair after splicing two appropriate cables together. This method involves using a kit to replace the entire Micro USB plug assembly, including the strain relief. After cutting off and discarding the Micro USB head, remove the outer insulation of the cable, strip the the USB wires within and tin them. If the outer insulation is a fabric braid type, then melt the tip of the insulation with heat to stop it from unravelling.

Next up, slide on heat shrink (for cable bend relief), and then the Micro USB plug housing. This stage is probably easiest to forget. I can’t count the number of times, I have made a really nice soldered connection, only to undo it because I didn’t remember to slide on heat shrink beforehand. It’s funny, it only really happens on the more permanent joints, like the Western Union splice. I think its because I tend to be too preoccupied with making a good strong connection, that consequently: these types of things tend to slip my mind at the time. So take your time and do things methodically.

Just as an aside: heat shrink, in my opinion makes a good form of bend relief for a cable because it makes the cable a little stiffer along the length leading into the plug. This gives it resistance to bending to extreme angles, or allowing repetitive bend or flex damage to concentrate on a singular point on the cable. As for strain relief for the solder joints on the plug base: adding heat shrink to the cable does little. Id est it doesn’t prevent tugging force on the cable from exerting strain on the soldered connections between the cable’s wires and the Micro USB base’s pads. I’d carefully tie the cable end into a loose overhand knot (if it is of a thin enough gauge to do this), making sure not to cause any acute stress points in the wires as a result. This knot will act as a stopper against the insides of the Micro USB plug’s plastic housing. I am not sure whether or not this is generally advisable protocol, I am just stating what I tend to do. The loose knot offers some resistance to a tugging force as it tightens against the hole in the plastic housing. This in turn relieves the solder joints of some of the strain. Alternatively, filling the Micro USB plug’s housing with hot glue will also act as a decent form of (tugging) strain relief for the solder joints. These two methods do this by redirecting the pulling force away from the solder joints and into the housing and general superstructure of the plug.

Moving on. Now with everything in place, solder the USB wires to their respective pads on the Micro USB plug base. This includes the cable’s outer conductive shielding if present. In order to know which pads correspond to which pins: refer to any user guides or datasheets that may have been shipped with your spares kit. Alternatively test the continuity of the pads to the pins using a multimeter and a female Micro USB breakout board.

To connect the cable’s shielding: roll the loose strands into a cord. You may need to wrap this cord with another wire to extend it enough to reach the Micro USB plug’s outer metal housing. Which is a little further away than the USB solder pads on the example kit I have. I needed this extension to the shielding cord because when I cut the cable, it made all the internal wires and strands equal in length, so an extension was necessary in my case. After scratching off the finish on the part of the Micro USB plug’s metal housing that you intend to solder onto. Apply a small patch of electrical tape to insulate the USB wires from the shielding connection. Next, solder the shielding cord to the metal housing. You may need to apply solder to the twisted shielding cord to harden it and fuse the extension if necessary.

Now. Isolate the internal USB wires from each other, by injecting hot glue over and between the four wires. I use the electrical tape from before as a backing for this. I chose to have the adhesive side facing the USB wires, because I intended to wrap it around them at this stage. After this, pull the heat shrink into position then apply heat. Pull the plastic housing over the plug base and align the plug so that it is straight. I used the plastic cap to set the plug’s position. Once satisfied with the plug’s position within it’s plastic enclosure; remove the plastic alignment cap again and inject hot glue to fill any cavities between the plug base and the enclosure. Reapply the alignment cap. Then carefully apply some heat to the now closed plastic housing to make the hot glue within the enclosure melt into all the crevices and hold the alignment cap on. Be careful here because using too much heat can easily damage the plastic enclosure and alignment cap. Once that is done you are effectively finished.

Testing Phase

Although I tend to test at each discrete stage of a repair, for things such as bridged connections between pins or for consistent continuity across connections. I also recommend a final testing phase where we test the resistance of each wire using a USB 2.0 type-A female breakout board and a USB Micro type-B breakout board; or whatever the appropriate boards for the cable you are testing are.

The reason why I do this is to make sure that all the lines are of appropriate conductivity. In other words there aren’t any spikes in resistance in any of the lines that may cause problems when in use. This is especially true for data lines, where resistance will damage signal integrity. Although it is also important for power lines in use-cases involving higher current draws (around 2-3 Amps), such as those used in ‘fast chargers’. If there is sufficient resistance on the VBUS here it will retard the device’s ability to draw power across the cable.

Examples of improvised testing adapters

picture of a partially repaired USB cable inserted into some adapters for testing.

picture of 2 USB type A plugs. One has been stripped of insulation to be used for testing.

It’s generally good protocol to have a control test for comparison when testing your repaired cable(s). In this case I used a Samsung brand, model: U2 APCBU10BBE data cable that came new with a smart phone purchase. Please note: the control cable used here is not designed for higher current draws, it’s device needed a maximum of around 700mA to 1 amp when charging.

(Control) Samsung (U2 APCBU10BBE) data cable:
VBUS: 0.2 ohms
D-: 0.3 ohms
D+: 0.3 ohms
GND: 0.4 ohms
Shielding: none
Cable length (approx.): 1 meter

(Testing) Repaired w/kit yellow cable:
VBUS: 0.2 ohms
D-: 0.3 ohms
D+: 0.5 ohms
GND: 0.6 ohms
Shielding: 0.1 ohms
Cable length (approx.): 1 meter

(Testing) Repaired w/spares red braid (‘fast charge’) cable:
VBUS: 0.2 ohms
D-: 0.3 ohms
D+: 0.2 ohms
GND: 0.1 ohms
Shielding: none
Cable length (approx.): 2 meters

picture of a new USB 2.0 type A to USB Micro type B cable, connected to some breakout boards used for testing. This cable was used as a Control test.

picture of a spares repaired USB 2.0 type A to USB Micro type B cable, connected to some breakout boards used for testing.

picture of the USB type A female socket breakout board and USB Micro B female socket breakout board used for testing.

picture of a kit repaired USB 2.0 type A to USB Micro type B cable, connected to some breakout boards used for testing.

As you can see, they tested close enough that I feel that the cables that we repaired are of an appropriate quality, at least for me to have enough confidence to press them into service. Alternatively instead of using a control test for comparison, if you manage to find a datasheet for a particular cable you wish to replicate. The data from the datasheet can be used as a target instead. I just found it easier to see how my everyday cable fairs, then try to ape it’s stats. Consequently I do not have a concrete idea of what the resistance tolerances and acceptable margins are for these cables to maintain signal integrity while in use. But I am confident from the comparisons with the control cable that we are within them.

However, if say a cable tested (pulling numbers from my … hat) 15 ohms on a data line. I would inspect the repair, if it seems fine: then the problem could be with the cable itself. For example: such as in a wire where many of it’s hidden internal strands have broken due to repeated localised flex damage. So all the current is having to pass through just a few strands at that point, causing an invisible bottleneck. This should have been tested for at the initial stages of a repair when the cable was first cut and the wires exposed. But still, finding this fault at this stage, allows you to make the informed decision on how to go forwards, either demote it to a power only cable (and mark it as such), scrap it for parts, or find and fix the newly discovered fault.

Eventually, once you reach a stage where you are confident in a cable’s performance, the repair is truly complete and it is now ready to use. Done. This time for real. Thank you for reading.

References / Sources / Further Reading:

https://en.wikibooks.org/wiki/Serial_Programming/USB#What_is_USB?
https://en.wikipedia.org/wiki/USB
https://en.wikipedia.org/wiki/USB_hardware
https://en.wikipedia.org/wiki/USB_On-The-Go
https://en.wikipedia.org/wiki/USB_(Communications)#Signaling_state
https://www.ifixit.com/Guide/Micro-USB+Port+Replacement/73401
https://www.portplugs.com/how-to-repair-a-loose-micro-usb-port/
https://www.youtube.com/watch?v=36CKsP9YQ1E [why does USB keep changing – NostalgiaNerd]
https://goughlui.com/2014/10/01/usb-cable-resistance-why-your-phonetablet-might-be-charging-slow/
https://www.mschoeffler.de/2017/10/29/tutorial-how-to-repair-broken-usb-cables-micro-usb-including-data-transfer/
https://www.mouser.com/pdfdocs/HiroseZX62Datasheet24200011.pdf
https://www.howtogeek.com/670644/what-is-fast-charging-and-how-does-it-work/