@all,
Happy New Year!
Update on testing the board.
- The board passes all the tests in the automated test sketch (i2c bus, FRAM, RTC, User Switch, Temperature, Alarm functionality, RTC triggered Power down sleep)
- I did make a mistake in the schematics above that cost me a FRAM chip. My Programmer (Sparkfun AVR Pocket Programmer) provides only 5V power which is above the absolute max the FRAM chip can stand (4V). So, I made a slight change to move the ATTINY Vcc on the output of the diode. That way, no matter what devices you may chose to put on the board, they will not see 5V.
- I was able to load the TinyWireS library on the ATTINY and validate that it is showing up as an i2c device for the Boron. I have not yet started writing the new watchdog code with programmability but will work on this while the board is being manufactured.
- I spent some time working on the IO connectors and came to a few realizations which I wanted to share:
- Seeeeeeeed Studios Grove is not a standard JST socket - so they are out.
- JST SRT series 1mm pitch connectors are remarkably robust and save a lot of space on the board.
- There are a number of sources for JST SR/SH pre-crimped cables and kits so the fact that the crimping tool costs SEVENTEEN HUNDRED DOLLARS!!! is not as big a deal as I thought. I will share more on this in a separate thread.
- Pre-made cables are easier to find in 4-pin and 6-pin configurations so I standardized on them.
- Qwiic cables and board to board cables need to be “Reversed” I almost fried a new Sparkfun TOF board with this mistake.
- There is absolutely no agreement on pinouts for standard headers (serial, SPI, Analog IO, i2c with interrupt pins) except for Grove (see above) and Qwiic. So, I put a Qwiic port on the board and followed their convention for the other headers. This means I had to put Vcc next to ground but I held my nose and did it for consistency.
Next steps:
- I plan to send this board to MacroFab for a small run ~20 in the next day. These boards will be expensive $65 because it is low volume. I will then field these boards (assuming the Boron Solar fix works).
- You can order bare PCB boards from OSHPark here.
- Once I validate the next batch, I will do a much larger run to bring the board costs down to about $30 and would be happy to include others in that run to help increase the volume and lower everyone’s costs. I am not trying to make money on carrier boards so, I am opening this for the mutual benefit of a larger run for the community.
- I will share everything including the EAGLE files so you can take this project and make the changes that best suit your needs.
Please take a look and let me know if you have any comments. After this first production run, I think I might start a few new threads (higher volume community run, JST SR/SH Qwic cables, Watchdog Timer).
Thank you as always for your help and support.
Chip