I’m after a 4 core cable that is flexible. It will connect BNO85 to PCB via I2C - using STEMMA QT connectors. Is the easiest solution to splice with short wires that have the STEMMA QT connectors already attached? Or should I crimp the wires? Or is there another option?
The wires will need to be long in length (1m-2m) and will be used in a wearable application where the BNO85s will be on the legs and PCB will be on the wrist (the wires will be “embedded” in the clothing. I have run the code with this wire length and with some error handling, it works with this wire https://au.element14.com/pro-power/ac-t3-4c-blk-100m/alarm-cable-4-core-type-3-black/dp/3382516- but it is not flexible enough.
Core has a similar item but it appears that it is only available in 1M lengths, and I presume you don’t want joins in the middle of the run.
Crimping the wires for yourself is by far the best option as you get exactly what you want. If you haven’t done it before then allow for a bit of practice. It’s not difficult but there is definitely a knack to it.
You’re on the right track looking for flexibility, silicone-insulated wire is truly the way to go for wearables. PVC-based alarm cable is too stiff for embedding in clothing.
If you want to use the Adafruit-style silicone ribbon cable or similar, here’s how you can do it cleanly:
Option 1: Splice pre-crimped pigtails: You can buy JST-SH pigtails (STEMMA QT style) and solder or splice them onto your silicone ribbon. It’s the quickest way, but makes a joint in the garment.
Option 2: Crimp your own ends: This is my go to for most projects I do. It provides a durable connection and after doing a few you start to get the hang of it. We’ve got a wide range of crimpers, from the lower end SN-01B up to the Pololu 1929
If you find something that suits then silicon 4-core stranded cable would work fine. The advantage of the ribbon cable is that it lays flat under clothing, and is more flexible because it doesn’t need the extra sheath to contain the cores.
It doesn’t look like Core Electronics stocks the individual housings and pins, but searching for “JST SH Connector Housing 4 Way” should point you in the right direction.
The terminal has to be correct for the connector, but the wire can be any gauge that can be crimped in the terminal. However I am sure there is a 28AWG version of that product if you prefer.
Good question, it might be best for you to look for 28AWG Silicone Ribbon Cable 4Pin Cable Flexible Silicone Wire 10m/32.8ft to be safe with the connector.
That’s a list of 25 different connectors. Which one are you using? What is the wire gauge? What is the result? For instance, the connectors don’t seem to fit the tool, the wire doesn’t seem to fit the connector, the wire slips out of the crimping, the crimped connector can’t be fit into the housing, or something else.
The crimp terminal linked above doesn’t seem to fit the tool. The tool is too wide that I can’t manoeuvre how is needed and described in the how to crimp video. I tried just doing it other ways starting it off with pliers but can’t get it to work
If the tool seems too wide I assume you mean the width across the jaws, not the gap in the shaped crimping groove. If the problem was the gap in the groove you would be able to place the terminal, but the crimping might not work, but it seems the problem is placing the terminals. The terminals you have referenced are apparently 3.9mm long. That is very tiny. The smallest I use are 6.25mm, and I find them quite difficult to place in the crimper. Based on that size, and your description of the problem, I suspect that those terminals are not designed for hand crimping tools, and if they were then that is probably the wrong tool. The SN-01B is not specified for terminal sizes with a pitch less than 2mm, and overall size is related to pitch. It appears that the ‘official’ crimper for those terminals retails at over USD1,000! Do you really need a connector with 1mm pitch?
Hmm 1mm pitch connector is what I have on the PCB, I could change it and reorder PCBs. But at this stage I’m just after one prototype so it wouldn’t be worth it. Soldering to already crimped connectors will probably be the best solution I imagine? Cost is a factor - trying to keep it low
Hi Mitchell, Jeff, Ryan
I was going to stay right out of this one but when you start on small connectors you really do open up a can of worms.
There are so many out there seemingly with their own “specifications” it is a bewildering job trying to keep track.
Doomed to failure I think before you even start. As Jeff states above a lot of these very small crimps require some specialist tooling, mostly in the thousands of $$ range. And nothing else will successfully do the job. And as Jeff says they are quite difficult to use without a lot of experience.
Another important bit is wire size. Mostly quoted in AWG (American Wire Gauge, or Gage as the Americans spell it). It seems even if the wire is manufactured locally. In this case sizing is quoted in square millimetres or the stranding size ie; 7/0.2 which is 7 strands of 0.2mm diameter wire, very few, if any of these are exactly AWG sizes. Most are pretty close but NOT the same. This is not so important as the crimps are somewhat forgiving, hence a crimp quoted as suitable for a range of sizes.
Probably just as important is insulation thickness. Our insulation thickness is something like double the American standards which showed up some time ago when I attempted to assemble some crimped pins into housings like sold by Core SKU Pololu1903 using pins Pololu 1930. Pins crimped successfully using a ratchet crimper but would not fit into the housing as the overall wire diameter was too large. Even the wire used was supposedly within the connector range. I realised then that if I had used American manufactured wire the pin would have been quite OK fitted into this housing. This is I think an oversight and a trap easily fallen into.
Result. The pins and housing made to American "standards or specifications do not work sometimes with locally produced wire even if sold as AWG sizes.
I suppose we are a bit lucky these days as we seem to only deal with AWG and metric sizing. Years ago there were several “Gauge” standards and they were all different. Indeed it is still the case where the actual “size” of a gauge depends on the material. ie copper is different to iron and aluminium etc.
Cheers Bob
PS I have a chart somewhere with all these different “Gauges”. I think there are a number of these on line.
