Please see my rep[ly #505 earlier in this thread... repeating much of htat her, plus a couple more points and a bit more clarification of my concerns.
I consider I2C level translation a critical feature... This is a life sustaining device used under relatively uncontrolled conditions. I can't accept using a marginal spec communications link for safety critical pressure monitoring. I'd also use the lower value pull-ups on the 3.3V side of the interface... Unknown signal line capacitance... the lower values give us more margin.
ESD/EMI mitigation - Protection on lines in and out of the device... Maybe for a second spin of the board. The first spin gets it into developer hands.
A larger pcb now allows for additional circuitry later such as esd/smi mitigation, while not requiring a change in the housing.
o???I2C level translation… Note load options of R105, R106 bypassing the MOSFETs… Builder’s choice.?Running on the edge of spec for 3.3V parts on a 5V system… I’d absolutely use the translator.
o???I also use lower value resistors on the downstream side of the I2C bus…?Long lines, increased capacitance, increased exposure to noise. ?1.47K as shown adds some reliability…
o???10-pin connector for additional analog and digital I/O including serial port pins. Addresses known needs - analog pressure sensors. Probably don't need all 10 lines, but I'd bet a few of them come in handy...
o???Input power fuse - again a safety feature.
o???(Input battery voltage / 6) provided to an analog input for Arduino monitoring of the supply voltage and possibly triggering alarms based on same. A safety feature. I'd implement supply monitoring in hardware removing the reliance on firmware, but recognize the constraints on the project!
o???Test points for all DC voltages
o???M3 mounting points
o???Not yet added… silkscreen field for revision of pcb, space to mark the BOM revision…
