Thursday, October 30, 2008 Relays

Here is a simple cycle control circuit for a two-stage prop. Requires two 12 volt relays and two momentary switches (with "normally closed" terminals).

Switch 1 is mounted to be actuated when the prop is in the "at rest" position. Switch 2 is mounted to be actuated when the prop arrives at the "full scare" position. A negative trigger (either from you or a motion sensor, etc.) causes Relay 1 to 'latch', and in turn activates the Relay 2 to provide 12 volt power to the wiper motor. When the prop pops up or does whatever its thing is and hits Switch 2, the latched relay deactivates and stops the motor. The prop is then reset by a second negative trigger (either from you or a timer) which provides power to the motor to return the prop to its ready position.

If your prop requires just one cycle - meaning it triggers, does its thing and returns to its original position in one continuous motion, only one momentary switch would be needed.

This configuration worked quite well and was cheap to make. NOTE: the 12-volt power feed needs to be fused for safety.

This control circuit was posted on the HauntForum by TommaHawk. It offers all of the functionality of the first circuit and adds the ability to reverse the polarity (and therefore direction) of the motor.

This is an old hack that I did to a cheap RC car in order to use the radio control circuit to control a larger prop powered by two wiper motors and a lawn tractor battery. It actually worked well, given the limited range of the toy. I ended up doubling the length of the receiving antenna and that helped. This completely mobile style of prop is fun, but really offers potential for injury.