I am trying to attach a quadrature rotary encoder via my Arduino to my computer. Since there need to be other systems attached tot he same Arduino which need to be controlled I have a StandardFirmata sketch on it. My idea is that I could read the digital pins for a change (True/False) while I turn the encoder. I then wanted to compare the current state with the previous state to check for a change of state (somewhat like the attachInterrupt function in Arduino):
import pyfirmata
pin3_now=0
pin3_before=0
counter=0
time=core.Clock()
board=pyfirmata.Arduino('COM4')
#Use iterator thread to avoid buffer overflow
it = pyfirmata.util.Iterator(board)
it.start()
pin3 = board.get_pin('d:3:i')
while time.getTime() < 10:
pin3_now = pin3.read()
pin3_before = pin3_now
if pin3_now != pin3_before:
counter= counter+1
print counter
board.exit()
However, the if statement is never executed. If I print pin3_now I can change the values changing form False to True and vice versa. I do not understand why the if statement is not executed although a change of state is clearly visible.
I tried putting the values in a list and compare elements of the list. This works, however the detection in change of state is then limited how fast the values are inserted into the list, making a calculation of velocity impossible.
import pyfirmata
y_list=[]
pin3_now=0
pin3_before=0
counter=0
#pin4_now=0
#pin4_before=0
time=core.Clock()
board=pyfirmata.Arduino('COM4')
#Use iterator thread to avoid buffer overflow
it = pyfirmata.util.Iterator(board)
it.start()
pin3 = board.get_pin('d:3:i')
#pin4 = board.get_pin('d:4:i')
while time.getTime() < 10:
pin3_now = pin3.read()
pin3_before = pin3_now
y_list.append(pin3_now)
if len(y_list) > 20:
y_list.pop()
# Get the velocity
if y_list[0] != y_list[-1]:
counter= counter+1
# if pin3_now != pin3_before:
# counter = counter+1
# else:
# pass
print counter
board.exit()
Could someone explain this phenomenon to me and how I can correct it (or has someone else a better solution to detect the change in state) ?
Thank you in advance