So far in Object class, we have been learning about basic elements of circuits and different kinds of circuits, including series and parallel configurations. In this three-part lab, we built simple series and parallel circuits with LEDs and switches, constructed a DIY switch using materials from lab, and designed a creative enclosure for our breadboard and circuits.
Part 1: LEDs in Series and Parallel
For the first part of the lab, I created a series circuit and a parallel circuit using nothing but a breadboard (prototyping device with conductive material and places to stick wires), jumper wires, resistors (components that provide resistance against the electrical current so you don’t overload your system), switches, and LEDs. First, I decided to use a regulator to decrease the voltage of my 9V power source to a more appropriate 5V. It was confusing at first, but our guest instructor Melissa helped me to hook my power up to the regulator. Now, I was ready to start building the rest of my circuit.
One of the hardest parts of this first circuit-build was figuring out what kind of resistors I would need to use in order to get the right amount of current for my LEDs. I looked up the datasheet for a standard yellow LED on Sparkfun’s website, and this told me that yellow LEDs need about 2 volts of voltage (Vf, or forward voltage) and 20 milliamps of current (I), or .02 amps. At this point, I knew that my starting voltage (Vs) would be 5V, so I could start plugging things into Ohm’s law, which is: (Vs-Vf)/I = R. R stands for resistance, in ohms. My calculations are below, and I determined that I would need a resistor rated to at least 150 ohms. There were no resistors available for exactly 150 ohms in my workspace, so I used the next size up, which was 220 ohms.
Now I was ready to start plugging things into my breadboard. I had already connected my power jack to a voltage regulator that would reduce the voltage from 9V to 5V, then connected the output line of that regulator to a switch. After the switch, I added my resistor and an LED, running the negative end of my LED back to the ground line on my breadboard (which connected back to my power jack). Once I was certain my circuit worked, I added the second LED into the circuit right after the first one to be in series with it. Below you can see a photo of my series circuit!
To change my circuit to be in parallel instead of series, I only had to make a few changes. I removed the second LED from the circuit and made sure that the first LED was still connected to ground. Then, I added a new 220 ohm resistor to the output of the switch and placed an LED after that resistor, connecting it back to ground (the red LED had the same values for voltage and current in its datasheet as the yellow one, so I was able to re-use my resistor calculations). In this way, electricity was able to run separately through both LEDs. If I unplugged one of them, there would still be a complete circuit through the other LED. Here’s a photo of the parallel circuit:
Here is a sketch of my schematics for both the series and parallel circuit. As you can see, the series circuit channels electricity through one LED and then the next, while the parallel circuit channels electricity through each LED separately.
Part 2: DIY Switch
For the second part of this lab, I had to construct a DIY (do-it-yourself) switch. A switch is essentially a part of your circuit that can be disconnected, stopping the flow of electricity. There are at least two contact points on every switch. When the two points are connected to each other, electricity can flow from one to the other and complete your circuit. Otherwise, when the switch is “open,” the contact points are not touching and the circuit won’t work.
I was inspired to use conductive tape for my switch, so that all I had to do was integrate the tape into my circuit and create a way for the ends of the tape to connect and disconnect, either completing or disrupting the circuit. My first problem was figuring out how to connect my jumper wires to the tape. Since I could stick the tape right onto my breadboard, I tried pushing one of the ends of my wire through the tape, which actually worked! Then, I used some foam to build up a barrier between the contact points, and laid another piece of tape on top of the foam. This way, when someone pressed down on the top piece of tape, it would touch the bottom piece of tape and connect the circuit. See a picture of my first prototype below!
Once I knew my switch worked, I decided to cover it with a big piece of foam that the user could press, to make it more intuitive. Here is a video of my first switch in action!
Part 3: Creative Enclosure
At last, time to make my creative enclosure! The assignment was to create an enclosure to hide all of the electrical components in a creative way, so I decided to create a little house with a window that light could show through. To construct the house, I cut up pieces of felt and stuck them onto the breadboard and to each other. I actually took apart my switch from Part 2 so that I could re-construct it in a more efficient way. Below are some photos of the construction of the house and the new custom switch.
Video of my switch in action:
After continuing to build the rest of the enclosure, I ran into a problem. My switch started working less consistently. I determined that the connectivity problem was due to a fragile connection between the switch tape and jumper wire, so I decided to take out the top piece of conductive tape and just use the end of the jumper wire as the second switch contact point. See the photo below! This greatly improved the reliability of my switch.
After completing the walls of my house, constructing a window by taping a piece of plastic and a tissue to a piece of felt, and topping everything off with a simple ceiling, my house was complete! Check out a video of the final project below!
nate bennett 