Faster quadrature decoder loops with Python code
- by Kelei
I'm working with a BeagleBone Black and using Adafruit's IO Python library. Wrote a simple quadrature decoding function and it works perfectly fine when the motor runs at about 1800 RPM.
But when the motor runs at higher speeds, the code starts missing some of the interrupts and the encoder counts start to accumulate errors.
Do you guys have any suggestions as to how I can make the code more efficient or if there are functions which can cycle the interrupts at a higher frequency.
Thanks,
Kel
Here's the code:
# Define encoder count function
def encodercount(term):
global counts
global Encoder_A
global Encoder_A_old
global Encoder_B
global Encoder_B_old
global error
Encoder_A = GPIO.input('P8_7') # stores the value of the encoders at time of interrupt
Encoder_B = GPIO.input('P8_8')
if Encoder_A == Encoder_A_old and Encoder_B == Encoder_B_old:
# this will be an error
error += 1
print 'Error count is %s' %error
elif (Encoder_A == 1 and Encoder_B_old == 0) or (Encoder_A == 0 and Encoder_B_old == 1):
# this will be clockwise rotation
counts += 1
print 'Encoder count is %s' %counts
print 'AB is %s %s' % (Encoder_A, Encoder_B)
elif (Encoder_A == 1 and Encoder_B_old == 1) or (Encoder_A == 0 and Encoder_B_old == 0):
# this will be counter-clockwise rotation
counts -= 1
print 'Encoder count is %s' %counts
print 'AB is %s %s' % (Encoder_A, Encoder_B)
else:
#this will be an error as well
error += 1
print 'Error count is %s' %error
Encoder_A_old = Encoder_A # store the current encoder values as old values to be used as comparison in the next loop
Encoder_B_old = Encoder_B
# Initialize the interrupts - these trigger on the both the rising and falling
GPIO.add_event_detect('P8_7', GPIO.BOTH, callback = encodercount) # Encoder A
GPIO.add_event_detect('P8_8', GPIO.BOTH, callback = encodercount) # Encoder B
# This is the part of the code which runs normally in the background
while True:
time.sleep(1)
