Pictured below is a controller for an automatic horse feeder. This device is made up of a 12V digital programmable timer, a microcontroller board, and an eight relay board.

The horse feeder hardware comprises four shelves onto which the owner can put feed. Four car door locks are used to release the shelves one at a time to release the feed and drop it down to where the horses can access it.

When 12V at one polarity is supplied to a lock, it will perform a pull action; when the polarity is reversed it will perform a push action (which resets the lock ready for the next time it is to be used).

The programmable digital timer is set by the end user to turn ON for one minute at the times of day that the horses need to be fed. Our controller (pictured above) receives power when the timer is ON, decides which feeder should be released next, pulls the corresponding lock to release the feed shelf, waits a couple of seconds, and then pushes the lock to reset the feeder.

To enable the polarity supplied to the locks to be reversed, eight SPDT relays are used for which we used a commercial relay board (click here to buy relay boards of this type). We connect 0V to all the relay NC’s, and +12V to all the relay NO’s, then for each pair of relays, we connect the COM’s to the lock power inputs.

If we close one relay in a pair we get one polarity supplied to the lock (since it sees +12V and 0V), and we we close the other relay, we get the other polarity (since it now sees 0V and +12V).

If you have a process to automate in a way similar to this example, email neil@reuk.co.uk with details of your exact requirements.