Second assembly and testing

A project log for Mothra: Acoustics Laboratory on a Stick

STM32WB55 host with microphones and accelerometers and lots of memory for vibration and sound analysis

Kris WinerKris Winer 03/22/2021 at 04:200 Comments


Got the revised pcbs back from OSH Park and put a couple together today.

Happy to say no shorts or design errors....yet.

Thomas Roell provided a preliminary Arduino core for testing the boards. I was able to blink the three RGB leds, read MCU temperature, and read battery voltage. I found all three I2C sensors on the internal I2C bus and was able to get the BMA400 to wake on motion and sleep on no motion. I verified I could record the sound of my voice using the ICS41350 PDM microphone. I verified BLE Tx using the Nordic UART service.

The RSSI of the module was around -50 dB when close to the smartphone. This is a little bit worse than what I have measured using the Firefly with the discrete STM32WB55 and its pcb antenna, which was somewhat surprising.

We have some more software development before we can test the IIS3DWB. And for some reason I wasn't able to get the SD card to work yet. Still, for one day's worth of assembly and testing the design seems to be working about as well as can be expected.

I ran a simple blink sketch with the MCU put into STOP mode for five seconds at the end of the main loop and used an ST power meter to check power consumption. The Mothra device is using ~210 uA in STOP mode, where it really should be using ~20 uA. So somewhat of a mystery here as to what is causing the extra 10x power usage in low power mode.  

Early days, still a bit of work to do before we can start using the device as intended...