I’m looking at purchasing a Teensy 4.1 in The Netherlands, and I see there’s an option available without ethernet functionality. I noticed in the auxiliary build instructions that we use stripped ethernet cables for sensor connections. I’m assuming this is simply because ethernet cable provides a convenient 8-wire bundle rather than because we actually need ethernet connectivity.
Before I place my order for the Teensy 4.1 without ethernet, can you confirm that we don’t currently use any ethernet functionality with compass? Any reason why I need to switch suppliers and go for the ethernet option?
Thanks Cam! Going with the cheaper option then thanks for the swift reply! Eagerly awaiting the pcb kit, which will arrive any moment now; along with a big AliExpress order I just put with the back2school event.
Excited to bring your passion project into IRL and to start tinkering with and on it!
Another question Cam.. I took a look at the ethernet cable setup for the sensors and the custom assembly you had made from China. I can try and crimp an off-the-shelf ethernet cable, but couldn’t I just buy a 200mm JST GH 8-pin cable assembly like this one on Amazon?
Seems much simpler than stripping ethernet cable and crimping those tiny JST GH pins. Am I missing something, or would these work just as well? The only difference might be no shielding, but for short sensor runs would that matter?
Just trying to save others the crimping hassle if there’s an off-the-shelf solution!
Hey Arnoud, great question. Those cables might work fine for a bit, but the ethernet cables are used to make the SPI connection more reliable. I was using simple ribbon cables on my initial prototype. They worked for a bit, but quickly proved to be insufficient. SPI is not supposed to used on long runs, let alone on cabled runs. We have to do some sneaky things to make it work well for our situation. Ethernet cables are the main thing. The twisted pairs of the ethernet cable help minimize noise and crosstalk in the SPI bus (I’m probably not explaining this perfectly, but smarter people than I have proved this to work well lol), making for much more reliable communication. Each SPI pin (MISO, MOSI, CLK, and CS) is paired with either ground or 3V. This isn’t quite differential, but it mimics a lot of the benefits
I was wondering why the boards use JST connectors instead of RJ45? Height profile or development debt?
Also, what do you think of using an RJ45 breakout board like this one https://nl.aliexpress.com/item/1005004520312413.html? I’d solder a very short JST pigtail to it to connect a standard CAT cable, keeping the untwisted length minimal. Seems like a good way to avoid crimping. Any concerns with that plan?
A combination of form factor and reliability. RJ45 gets pretty bulky, especially with 4 ports on one board. Also, I talked with Bar from Maslow about RJ45 usage (because he used them on his older boards) and apparently they become finicky when exposed to dust and/or vibration. He’s since switched to JST XH. I chose JST GH because they have locking features and are even smaller. They are actually used on hobby drones pretty often because of their robustness in high vibration and suboptimal settings.
You might be able to get away with that, but it’s going to be pretty bulky. It might be tricky to actually get that to fit in with everything. Also, the previous points about reliability still stand. I can’t guarantee that the communication will be perfect. If you want to avoid crimping, I would instead solder ethernet cables.
I’m planning on adding pre-made sensor cables to my shop soon, just waiting on the samples to arrive. A lot of people have been hitting a wall when it comes to the cables, so it seems like it might be a popular item.
thanks for the swift reply! Eagerly awaiting the pcb kit, which will arrive any moment now; along with a big AliExpress order I just put with the back2school event.