Motor control

Thread Starter


Joined Nov 15, 2009
Hi, I need an urgent help in :

I am building this device, which is a beam, to move in the forward and reverse direction. I have managed to get this working. The problem I have now is that to stop the motor when the beam is fully extended and stop it again when it is fully retracted. I want the motor to be reversed automatically when I give it a pulse, more like a water sensor pulse then the beam would be retracted. I know that I should use limit switches and relays but I can't come up with a circuit.I seriously need your help, it would be much appreciated !


Joined Dec 19, 2007
So, you want to push a button and have the beam extend until it hits a limit switch and stops. Then when you hit the button again (or a second button?...easier!) the beam retracts until it hits a limit switch and stops, ready for the next cycle.



Joined Jul 17, 2007
This is almost what you're looking for, but with two buttons:

If you don't want the relays to latch (thus keeping the motor running in the selected direction), remove D3/D4
If both relays are latched, the motor will stop. You would have to press S3 or S4 to get it to run again.



Joined Jul 17, 2007
This should work for what you're wanting to do:

The tricky part will be determining just the right size of capacitor to use for C1. You will need to experiment with different values of capacitance.

1,000uF is just a suggested starting value. The capacitor needs to be discharged about half way before the relay contacts close, otherwise when the limit switch closes as the motor pulls the beam away from the other end, the opposite relay may latch, causing the motor to stop. If the capacitor is too small, there will not be enough power to close and latch the relay.

S1 is a SPDT pushbutton. R1 limits the charging current from the +V supply; this will help prolong the life of the switch contacts. Without it, instantaneous current across the switch contacts will be very high, tending to burn them quickly.