Spencer Board Code

Spencer is the telemetry producer board. It samples sensors, packs a fixed 98-byte telemetry struct, and emits framed I2C chunks for SD logging and timed radio forwarding.

What This Firmware Does

• Samples GPS, BMP, magnetometer, and IMU data in loop().
• Tracks per-sensor validity bits in a packed telemetry packet.
• Sends framed I2C data continuously to SD receiver path.
• Sends framed I2C data to radio receiver path in a PPS-aligned window.

Data Path Overview

Sensors + GPS callbacks
        |
        v
Build 98-byte TelemetryData (validity + payload + I2C status bytes)
        |
        v
Chunk into I2C frames (max 32 bytes each, 2-byte header + up to 30 payload)
        |
        +--> destination flag SD (bit0) every loop
        |
        +--> destination flag RADIO (bit1) after PPS gate

Telemetry Packet Layout (98 bytes)

Field group	Bytes	Notes
packetCounter	2	Increments each send attempt
validity	1	bit0 GPS, bit1 BMP, bit2 mag, bit3 inertial
GPS block	28	lat/lon/alt/NED velocities/unix epoch
BMP block	8	float temperature and pressure
Magnetometer block	6	int16 x/y/z
Inertial block	28	accel xyz, gyro zyx, temperature
lastI2CBytesWritten	1	Saturated to 255
lastI2CStatus	1	Wire.endTransmission() status or short write
Reserved	23	Pad to 98 bytes

I2C Framing

Spencer sends telemetry as multiple frames, each up to 32 bytes total.

Item	Value
Max I2C frame size	32 bytes
Header size	2 bytes
Max payload per frame	30 bytes
Start-of-packet flag	bit7 in header byte 0
Destination SD flag	bit0 in header byte 0
Destination RADIO flag	bit1 in header byte 0
Header byte 1	8-bit checksum over payload bytes

Frame header byte 0 bit usage:

bit7  bit1  bit0
 START RADIO SD

Event and Timing Behavior

1. loop() reads local sensors and services GPS.
2. sendTelemetryPacket(I2C_FRAME_DESTINATION_SD) runs every loop pass.
3. PPS interrupt sets can_blink and time_of_last_pps.
4. After about 550 + pps_delay ms from PPS, one RADIO-destination packet is sent and gate is closed until next PPS.

GPS Handling Notes

• GPS callback (setAutoPVTcallbackPtr) updates telemetry when auto-PVT data is available.
• serviceGPS() also performs non-blocking fallback polling (getPVT(0)).
• GPS validity clears when update age exceeds timeout window.

Debug guide

Status LEDs (Teensy)

Signal	Pin	Meaning
I2C / activity LED	3	Driven HIGH for the duration of each sendTelemetryPacket() burst (framed I2C writes to Abraham and/or Jacob), LOW when idle between bursts.
Built-in LED	13 (LED_BUILTIN)	Short flash on each GPS PVT update in saveGPSData(). During boot, pin 3 or pin 13 may toggle while waiting for BMP, magnetometer, IMU, or GNSS to initialize.
PPS	15 (input, pull-up)	Not an LED: GPS pulse-per-second. On each rising edge, handleInterrupt() pulls pin 3 LOW.

UART / serial

This sketch does not open Serial or Serial1; there is no live UART log unless you add it.

• USB: Use the Teensy USB connection and the Arduino Serial Monitor if you add Serial.begin(...) for temporary prints.
• External USB–UART on Serial1 (Teensy 4.x): Use a 3.3 V logic adapter only. Wiring is GND, RX from the adapter to Teensy TX1 (pin 1), and TX from the adapter to Teensy RX1 (pin 0). Typical baud is 115200 if you match Jacob’s console.

Never connect 5 V TTL UART lines directly to Teensy I/O.

Tooling

• telemetry_packet_viewer.py decodes Spencer 98-byte packet logs and supports raw or terminated record formats.
• The viewer maps lastI2CStatus values to readable I2C status text for quick diagnostics.