This is one way the finished project could be mounted - the see-through-lid 220 x 70 x 80mm electrical box is available from electrical wholesalers for about $30, while the courtesy light (left) is a car reversing lamp, available at auto shops. The SLA battery fits nicely in this case, along with the PC board, and the plugpack keeps it nicely charged.

This controller uses an assembled UHF transmitter and receiver to make life easy for you. Output from the receiver is used to control the motor drive circuitry, the action depending on the pushbutton pressed on the remote transmitter.

It may be used to directly control a 12V DC motor for a garage door opener or gate opener, or (with appropriate care and safeguards) to control an external relay or contactor which in turn controls 240V or even industrial 415V (three phase) motor as often found on large and high roller doors.

While the circuit is complete, the details of the mechanical drive system for your particular garage door or gate opener are up to you. For inspiration, you might refer to our previous articles on a garage door opener in the April & May 1998 issues. Similarly, for a practical gate opener system, have a look at the August 1997 issue of SILICON CHIP.

Both the drive systems referred to are based on 12V automotive windscreen wiper motors which have the advantage of being cheap, readily available, powerful and compact.

This controller circuit suits those motors and incorporates a large 12V SLA battery as the power source. If you are considering a motor other than a windscreen wiper motor, bear in mind that most "straight" 12VDC motors will rotate too fast to be of much use in a garage door or gate opener. They need a gearbox to not only reduce the speed but increase torque.