Writing threads into code for 4 channel relay on pi

Hi John,

The periodic counter/tick system recommended by Frank and Cris is a decent way to implement this.

For what it's worth, here's some code just tried - it too uses a tick, in this case using some 'asyncio' library.

This only works with very recent versions of Python though (Python 3.8, and perhaps Python 3.7).

The beginning bit (lines 1-32) just sets up the framework for the ticks. Lines 33 onward handle the relay logic.

There is a tick for 1 second, a tick for 10 seconds, and a tick for 60 seconds. I just used the 1 second and 60 second ticks.

I'm a Python beginner (I don't like it much but slowly beginning to appreciate its usefulness) so I'm sure there are better ways to do it in Python, but this seemed to work. You'd need to replace or augment the lines containing print messages, to perform the actual relay switching.

It outputs a dot every second, a D every 10 seconds, and an M every 60 seconds, and a relay-related message after 3, 8 seconds and 5 minutes.

The program starts at line 67, because everything above it are functions.

#!/usr/bin/python3.8
import asyncio


PERIOD = 1.0
FOREVER = True
counter=0


# these three variables become 1 when 1, 10 or 60 seconds expire
event1=0
event10=0
event60=0


# counters for relays. rel1ctr counts in seconds, rel2ctr counts in minutes
rel1ctr=0
rel2ctr=0


# tick routine. This updates the event variables
async def tick():
  await asyncio.sleep(PERIOD)
  global counter, event1, event10, event60
  counter=counter+1
  if (counter%10==0):
    event10=1
  if (counter%60==0):
    event60=1
    counter=0
  event1=1


# main function which checks the event variables and handles the relay states
async def mainprog():
  global event1, event10, event60
  global rel1ctr, rel2ctr
  await asyncio.sleep(0.1)


  if (event1):
    event1=0
    print(".")
    rel1ctr=rel1ctr+1
    if (rel1ctr==3): # 3 seconds expired?
      print("relay 1 ON")
    if (rel1ctr>=8): # 3+5=8 seconds expired?
      print("relay 1 OFF")
      rel1ctr=0 # set back to zero so we can repeat the sequence for relay 1


  if (event10):
    event10=0
    print("D")


  if (event60):
    event60=0
    print("M")
    rel2ctr=rel2ctr+1
    if (rel2ctr>=5): # 5 minutes expired?
      print("relay 2 OFF")




print("set relay 1 off")
print("set relay 2 on")
print ("set relay 3 on")
print ("set relay 4 on")
while FOREVER:
  asyncio.run(tick())
  asyncio.run(mainprog())

shabaz your usage of https://docs.python.org/3/library/asyncio.html  does fit the Python language. My only question is why divide the Ticks from the mainprog logic? They could be done in just one routine as the .1 divides period 1.0 in exactly 10.

Thanks,

Clem

shabaz your usage of https://docs.python.org/3/library/asyncio.html  does fit the Python language. My only question is why divide the Ticks from the mainprog logic? They could be done in just one routine as the .1 divides period 1.0 in exactly 10.

Thanks,

Clem

Hi Clem,

You're right, no need to separate it. I just did it to make it look like a timer ISR (the tick function) and the main code. With a microcontroller I would have separated it, so the ISR is never hung for a long time, so I just repeated with the Python code, i.e. the tick will always execute fast, whereas the main code can be slow if desired. In the OP use-case there's no need for that as you say.

setting up another pi so i can play with some codes. i think i will start with yours shabaz. i actually have an old laptop somewhere with ubuntu on it also, maybe ill dig it out and update and use it for practice.