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EZ430 Chronos and the BeagleBone

Jun 20, 2012

Reading the accelerometer data transmitted by the EZ430 Chronos was one of the demos I had shown during the BeagleBone workshop on Jun 17th.

The ez430 chronos radio receiver brings up a serial interface when connected to the usb port of the beaglebone. Install the python2-pyserial module (on Arch Linux) and you can communicate with this interface easily:

pacman -S python2-pyserial

Here is a small Python library for reading accelerometer data:

import serial
import time

BAUDRATE = 115200
PORT = '/dev/ttyACM0'

def zerocrossed_up(prev, curr):
        return (prev < 100) and (curr > 200)
               
def zerocrossed_down(prev, curr):
        return (prev > 200) and (curr < 100)

def zero_crossed(prev, curr):
        return zerocrossed_up(prev, curr) or zerocrossed_down(prev, curr)

def port_open():
  fd = serial.Serial(PORT, baudrate=BAUDRATE)
  return fd

def start_ap(fd):
  cmd = '\xff\x07\x03'
  fd.write(cmd)
  print 'Access point start command given: response follows'
  for i in range(3):
    print hex(ord(fd.read()))


def get_acc_data(fd):
  cmd = '\xff\x08\x07\x00\x00\x00\x00'
  r = fd.write(cmd)
  r = fd.read(7)
  if(ord(r[3]) == 1): return [ord(x) for x in r[4:7]]
  return []

def main():
  fd = port_open()
  start_ap(fd)
  while True:
    r = get_acc_data(fd)
    if r: print r


if __name__ == '__main__':
  main()

Code is available on github