The folder contains the schematic files for the pico-pi header board. This provides us with the all the additional hardware functionality we need for a balloon tracker.
- 868MHz RFM96W LoRa Radio
- u-Blox MAX-M8Q GPS
- 144MHz and 434MHz Radios
- Microcontroller to act as watchdog
- Input diodes for solar panels
- optional ADXL345 accelerometer
We include a GPS Front End and a Chip Antenna. This choice of antenna trades off sensitivity for low mass, while the Front End mantains sufficient sensitivity and noise rejection.
Pi Zero uses a PAM2306 for power. Specifically it uses the KE variant for both 1.8V and 3.3V outputs. The camera supply comes from this 3.3V line.
We can reduce the voltage on the 5V net to about 3.5V as we're not using either the HDMI or USB sockets. This avoids having to include a boost regulator, which saves cost and complexity.
A supercapacitor prevents voltage droop and brown-out in periods of high demand or momentary solar panel shadowing. This allows us to use fewer solar panels, and means we don't need to profile maximum current consumption.
The Atmel SAMD20 microcontroller enables power to the rest of the system, and also acts as watchdog. The GPS and RFM95W radio are supplied by their own 3.3V LDO to reduce the load on the pi zero buck.
Accelerometer data might be useful, in particular it will give us pitch when taking photos. Could also be processed to quantify 'turbulence'.
The ADXL345 is an Aerospace Grade part with many common libraries.