Mechanical student needing help in electrics.... Pls help

Thread Starter


Joined Jan 31, 2008
Hi all, i've been tasked to activate a vibrating plate using a sensor. Both are connected to the mains but the sensor uses a step down to 24Vdc. Currently i'm trying to connect them using a relay but i do not know how to connect them. On the relay there are, (+ve) (-ve) Com, NO and NC.

The sensor has one wire as output while the vibrator has one yellow and 2 black wires. Can someone pls tell me if i'm correct to use a relay? and also which wire goes to which part of the relay? thank you! :)


Joined Nov 9, 2007
Think of a relay as a switch.

When the main contacts are closed a circuit is made and curent (power) can flow.

The opening and closing of the contacts are controlled not by a mechanical lever but by a secondary electrical circuit. You can get relays where current flow in the secondary circuit either hold the main switch open or closed. You can also get relays where several such switches are linked or ganged.

The point of this is that a small low voltage current can be used to switch a large, perhaps high voltage current whilst being isolated from it.

Thus a relay has at least four terminals
Two each for switch and control circuit.

Yes a relay is a very good choice for controlling the mains because of the isolation mentioned above and also because the mains is AC and your control circuit will be DC.

You may need a small electronic circuit to run the control terminals or a simple mechanical switch may be enough. Post again if you need help with control electronics.

Be very careful mains voltages can easily be lethal, make sure all high voltage stuff is properly insulated and the relay is sufficient for the job.