Lab 5: Switches And Relays

In this lab we learned about and experimented with switches and relays.  Switches can have multiple poles and multiple throw positions.  They are a good way to turn power on and off to the circuit without having to disconnect any components.  Relays use a low voltage or small current to flip between positions.  They are also categorized like switches in that they can be SPST, SPDT, DPST, DPDT, etc.  There is an iron core in the relay with a coil of wire wrapped around it.  When there is current flowing, a magnetic field forms around the iron core and pushes or pulls a lever (springy strip of metal).


After understanding how switches and relays work within circuits, we went ahead and build a circuit that included a push button switch, a DPDT relay, 2 LED's, connecting wires and a 5V power supply all connected using the solderless breadboard.  We ran the power through the relay so that the relay was switching on and off by itself when the pushbutton switch was pushed.  It looked like only one of the LED's was lit because the other one was flashing to fast to see it from the relay switching itself on and off.

You can see that the LED that lights up is controlled by the pushbutton switch.  The switch controls the current to the relay and when current is turned on or off, the relay powers one or the other LED's.



Capacitors act like batteries in a circuit in that they can be charged up and store energy.  Alignment is important when placing capacitors in a circuit.  The long wire needs to be connected to the positive side of the circuit otherwise the capacitor won't work.


A capacitor was introduced to the circuit by attaching the short lead of the capacitor to the negative side of the circuit.  We placed the leads of the capacitor on either side of the relay coil (bottom left and right pins) in the breadboard.  The capacitor charges when the current flows and when the contacts of the relay open, the capacitor acts like a battery and then sends power to the relay.  This cycle repeats over and over which causes the LED's to flash!

Lab 5 finished!