This is page 5 of 10 of a how-to on how to build an outlet/relay module. The main project page is here.
On this page, we're going to solder up the relay. The relay I used has 5 pins. 2 pins are for the signal lines (power and ground) to turn the relay on and off. The third pin is between the two signal pins and is the "common" pin. The 2 remaining pins are labeled N.O. (normally open) and N.C. (normally closed). What these mean is that when no power is applied to the signal lines (i.e. the "normal" condition), the circuit between the N.C. pin and "common" pin is closed (i.e. connected), while the circuit between the N.O. pin and the "common" pin is open (i.e. disconnected). Since the objective here is to turn something on when power is applied to the signal lines, we will be connecting the power lines to the "common" pin and the N.O. pin.
In this step, we'll solder the signal wires onto the signal pins. Cut 2 pieces of wire that are 3 to 4 inches long each. These are going to be the signal wires that will control the relay, so they can be smaller wires than the power cord. I used 24 AWG wire. Strip 1/8" to 1/4" of insulation off both ends of both wires. Solder one end of one wire to one of the signal pins on the relay. Solder one end of the other wire to the other signal pin on the relay.
In this step, we'll solder the power leads onto the relay. We're going to solder one end of the 5-inch wire to the N.O. pin, and solder the longer wire (in my case, the brown one) of the power cord to the "common" pin.
This step is entirely optional. In fact, I wouldn't expect anyone to do it. However, you may notice an extra part connected to the relay in some of my pictures, so I figured I better mention it so that it doesn't cause confusion. A while back, someone talked me into buying a bunch of parts called varistors. Varistors are a surge suppressor of sorts, so they are useful for putting across coils such as the signal pins of a relay in order to help surpress the voltage spike generated when the coil is de-engergized. Because I bought a whole bunch of these, I use them when it is at all appropriate, so I have connected the 2 legs of the varistor to the 2 signal pins of the relay (i.e. across the coil of the relay). I am not recommending that anyone do this step. Then again, I'm not recommending that you don't. What I will recommend is that regardless of whether you use a varistor, you should still use the diode across the transistor or microcontroller output pin that is standard in this situation. This is all that should be necessary to protect the output from the voltage spike from the coil.
Click here for an 3 minute video that demonstrates steps 5 and 6. It is about 7MB.
On to the next step - Construction part 3
Back to the previous step - Construction part 1
Back to my how-to index
Back to my Halloween index
Page last modified 03/28/2009