So today we wired up our first circuits. Before class started I put together boxes for each student with a breadboard, LEDs and a voltage regulator. When students came into class, I handed them their boxes and placed wires, batteries, alligator clips, wire cutters and strippers in the center of the room. Sitting on the floor, we started with nine volt batteries and LEDs with a forward voltage of 3V and a forward current of 0.03A. After using Ohm’s Law to figure out the resistance, we selected resistors and used alligator clips to make connections and light the LEDs.
The second circuit included a breadboard, a 12V DC power supply, an LM7805 voltage regulator, an LED and a resistor. As students were less confident about wiring up the voltage regulator and figuring out the new resistance, this circuit took a bit longer to complete.
voltage regulator detail
After a final wiring check, power supplies were plugged in, and LEDs lit up.
The next circuits involved wiring LEDs in parallel and in series. The challenge here was to see how many could be lit in series and how many in parallel.
Forty-five minutes goes fast. Even though all the materials were prepared ahead of time, I didn’t get a chance to cover LED properties or the resistor values involved with illuminating an RGB LED in the way that I planned. No one had time to wire up the Piranhas, or High-Flux LEDs, and no one had a chance to clean up before running to their next class.
| Type | Color | IF | VF Typ | VF Max | Luminous Intensity | Viewing Angle | Wavelength |
|---|---|---|---|---|---|---|---|
| Standard | Red | 30mA | 1.7V | 2.1V | 5mcd@10mA | 60° | 660nm |
| Standard | Yellow | 30mA | 2.1V | 2.5V | 32mcd@20mA | 60° | 565nm |
| Super bright | Red | 30mA | 1.85V | 2.5V | 500mcd@20mA | 60° | 660nm |
Well, tomorrow I’ll get another shot at it when the Middle School Physical Computing class works on their first circuits.
This assignment was inspired by Syuzi Pakhchan’s book Fashioning Technology and from the first circuit I made at ITP in 1998.
