Sequenced conveyor start and stop

Parts in this circuit

Wiring, pin by pin

Red = 5 V, orange = 3.3 V, black = GND, other colours = signals. “Pin” is the position on the 40-pin header; the GPIO number is what the code uses. Power the Pi from a 5.1 V supply and wire with the power off.

Python code (gpiozero)

from gpiozero import Motor, Button
from time import sleep

feed = Motor(5, 6, enable=12)         # belt 1 brings parts in
discharge = Motor(20, 21, enable=13)  # belt 2 takes them away
start = Button(27)
stop = Button(22)

DELAY = 3                             # seconds between belts

print("Press Start")
while True:
    start.wait_for_press()
    print("1. Discharge belt starts")
    discharge.forward(0.7)
    sleep(DELAY)
    print("2. Feed belt starts")
    feed.forward(0.7)
    print("Both belts running. Press Stop.")

    stop.wait_for_press()
    print("3. Feed belt stops first")
    feed.stop()
    sleep(DELAY)
    print("4. Discharge belt stops (it clears the last parts)")
    discharge.stop()
    print("Press Start to run again")

How the code works

• If the feed belt started first, parts would drop onto a belt that is not moving and pile up. So the belt that moves parts away starts first.
• On stop, the feed belt stops first and the discharge belt runs 3 more seconds to clear every part.
• wait_for_press() holds the program at that line until the button is pressed. The 3 second delays are the timers of a PLC program.
• Each belt has its own H-bridge: EN sets the speed, IN1 and IN2 set the direction.

Parts to buy

The links open a search on each store, so you see what is in stock today. Check the model, voltage and price before you order.