spi_sensor_reader

C++ SPI reader → POSIX shared memory (seqlock) → Python reader
~200 Hz sampling of strain gauges, power, and motor data.

Use this library to continuously poll sensor data and read it easily in Python.

Script should be continuously updated hook up more sensors.

Python Data Structure

{
    "seq": int,
    "sg1": {"ts": int, "values": [int, int, int]},
    "sg2": {"ts": int, "values": [int, int, int]},
    "sg3": {"ts": int, "values": [int, int, int]},
    "power": {"ts": int, "current": float, "voltage": float},
    "motor": {"ts": int, "throttle": float, "velocity": float}
}

Quick Start

1. Compile & run the C++ writerBash

   g++ -O2 -std=c++17 spi_shm.cpp \
      -lpigpiod_if2 -lrt -pthread \
      -o spi_writer
   
   ./spi_writer

   (keep this running in one terminal — Ctrl+C to stop cleanly)

2. Read sensor data in Python

   Use the class in your own code. See main in read_shm.py for reference, or

   from read_shm import SensorShmReader
   import time
   
   reader = SensorShmReader()
   
   try:
       while True:
           snap = reader.read_snapshot_dict()
           if snap:
               # Do whatever you want with the data
           time.sleep(0.005)  # ~200 Hz
   finally:
       reader.close()

Hardware

Current SPI setup (for Electrical reference):

Slave	CS GPIO	Description	Format
1	23	Strain Gauge 1	u32 ts + 3×u16
2	24	Strain Gauge 2	u32 ts + 3×u16
3	25	Strain Gauge 3	u32 ts + 3×u16
4	27	Power monitor	u32 ts + float I + float V
5	22	Motor controller	u32 ts + float thr + float vel

Bus: /dev/spidev0.0

TODO

Change to Power monitor GPIO22, Motor controller GPIO23, RPM GPIO24, remove SG