ITP Notebook

Lab: Switches

September 16, 2020

Physical Computing

Lab Guide

In this lab I learned about the various types of electrical switches and created a custom switch out of a coaster.

Making a Switch

I decided to turn a coaster into an electrical switch, so that an LED turns on when a modified mug is placed on it.

The coaster The coaster

The switch will be closed when the mug is on the coaster.

The closed state The closed state

To make this happen I used aluminum foil as a conductor, taping a pad of foil to each side of the coaster.

Two aluminum pads on either side of the coaster Two aluminum pads on either side of the coaster

Connecting to the foil using alligator clips, I measured for continuity. As expected, there was no continuity in the “unpressed” state.

Measuring no continuity on the empty coaster Measuring no continuity on the empty coaster

I then taped a strip of foil to the bottom of the mug.

Aluminum foil taped to the bottom of the mug Aluminum foil taped to the bottom of the mug

The multimeter beeped when I placed the mug on the coaster - continuity!

The connection becomes continuous when the mug is placed on the coaster

Now I needed to wire the switch to my breadboard. I used the same schematic introduced in the electronics lab.

Schematic view of a pushbutton controlling an LED. A DC power supply of 8-12V is connected to the input and ground of a 7805 5V voltage regulator. The output of the regulator is connected to a pushbutton. The other side of the pushbutton is connected to one side of a 220 ohm resistor. The other side of the resistor is connected to the anode of an LED. The cathode of the LED is connected to the voltage regulator’s ground connection Schematic view showing a pushbutton in series with a 220Ω resistor and LED

I connected one side of my custom switch to Vin and the other side to the input of the 220Ω resistor, which is connected to the LED and then ground.

Wiring the coaster switch to the breadboard by connecting one side to Vin and the other to the resistor's input Wiring the coaster switch to the breadboard by connecting one side to Vin and the other to the resistor’s input

Placing the mug on the coaster closes the switch, illuminating the LED. Success!

Placing the mug on the coaster closes the switch, illuminating the LED Placing the mug on the coaster closes the switch, illuminating the LED

It works!

One drawback to this design is that the mug must be placed at the correct rotation to close the switch. This could be avoided by creating a circular aluminum pattern on the bottom of the mug. That way the connection would occur no matter the mug’s orientation.

Other Switch Configurations

I also implemented two other switch configurations: switches in parallel and in series. With switches in parallel, pressing any one of them turns on the LED.

Switches in parallel: pressing any switch turns on the LED

With switches in series, you must press all of them to complete the circuit.

Switches in series: the LED can only be activated by pressing all three buttons