I looked it over, and I have questions.
- I don’t understand the choice of pin assignments for UART, SPI and I2C. Your assigns are perfectly OK, but please look at http://blog.touchstone-labs.com/2015/05/pin-assignments.html At the bottom of the page I suggest assignments that make the software tidy. I’m assuming that if all the pins are going to the same module are adjacent on the uC, it makes the routing cleaner, but I also realize I’m talking out my arse! So maybe the other DW signals should be on pins adjacent to the SPI?
- I was assuming that I’d use an external FT232 (as I have now) to carry debug info to the PC. But it looks like you are incorporating one for charging. That makes my life easier for sure, but does it soak up a lot of board space?
- On the DWM module it looks like p10 and p11 are grounded. I think p9 and p10 should be grounded to hardwire the SPI protocol details.
- Confirm that DW m_sync not connected to anything is OK. I don’t need it.
- As a general rule, it ought to be possible to turn off ALL the LEDs to conserve power, even those not under direct control of the processor. Jumpers, or scratch-out links would be good in places where the software can’t disable them.
- The more stuff we can get off the SPI the better, because the radio may have a limit to how long it can wait after raising an interrupt. So loading stuff (like the IMU) on I2C is slightly preferred.
- For some reason the Nordic standard is active low for buttons. Maybe there is some subtle power-saving reason?
- You mention a pressure sensor in the notes, but it’s not present (which is fine) FYI I think a pressure sensor can be attached to the IMU, rather than hanging off the I2C (or both?). I need to find out what the pros and cons are.
- I’m not sure what the benefit is of having a micro USB connector, and routing to the “USB and UART” J.
- Can you route 2 GPIOs to the SERIAL_COMM connector (nc-a and nc_b) pins to act as CS pins for any device we might want to experiment with. They can also act as triggers for a scope. Maybe they can be jumpered to LEDs by default?
- Maybe route 5V and 3.3V to same J connector too? No idea if this makes sense.
- Nordic pins 17,18,19 are ADC pins. I can imagine they might be useful for power experiments if they were easy to get at.
- You said the microSD card would suck power. We could leave it off. If space becomes an issue before the next rev (unlikely) then I can hang it off a J connector.
- Should the LTC2942 pin be routed to a Nordic GPIO so it can raise an interrupt?
- LTC3127. Should pin3 be under software control? Is it for forcing power-off when all hell breaks loose? What about pin 4. I never understood what it did in TS05
- LTC3105. What does SHNn do? How is it different from LTC3127p3? How would I use PGOOD? Should it be routed to a GPIO?
- Nordic pin24 is labelled PWRON. What does it do?
- Is there a convenient point to measure tiny currents other than with the coulomb counter.
- Need to connect the MPU9250 “INT” pin to the processor.