Electronics Lab

In the electronics lab, we’re learning about different ways of hooking up simple electronic components. This lab doesn’t require the Arduino, which also means we can’t make use of its integrated power regulator. Instead, we’ll need to solder up a power jack, and connect it to to the breadboard via a 5-volt power regulator (the power supply outputs 12v DC).

Soldering the power jack

Reverse of the 7805 5v DC regulator

With power flowing to the rails on either side of the breadboard, we’re able to use the multimeter to confirm a reading of 5.01v.

Next, we use a momentary switch, LED and a 330 ohm resistor to build a circuit.

A simple circuit

The voltage as measured at various points on the circuit is as follows:

• Across switch (open): 3.41v
• Across switch (closed): 0v
• Across LED (open): 0v
• Across LED (closed): 2.02v
• Across resistor (open): 0v
• Across resistor (closed): 1.91v

This makes sense. When the switch is open, no power flows to the LED or resistor. When the switch is closed, power flows to those components, and voltage drops across each. The closed switch provides no resistance, so there is no voltage drop across it.

The next circuit is simply two LEDs in series. Voltage drop across various components is as follows:

• + to LED1+: 0v
• LED1+ to LED1-: 2.69v
• LED2+ to LED2-: 2.40v
• LED1+ to LED2-: 5.01v

As the two LEDs provide adequate resistance (5.01v drop across the circuit), there’s no need for any additional components.

It really did read 5.01v when I pressed the shutter

The next step is to create a parallel circuit. For this, we’ll use three LEDs, and bring the resistor back in. Since the LEDs are in parallel, the voltage drop over each is the same (3.68v). Measuring current with the multimeter in series, we get a reading of 8.3 mA.

LEDs in parallel

Finally, we solder leads onto a 10k potentiometer, and connect that to a single LED and a 330 ohm resistor. Adjusting the resistance increases or decreases the voltage going into the circuit.

Varying resistance in a circuit from Jeff Kirsch on Vimeo.

The voltage ranges from 0v to 3.8v. The LED doesn’t come on at all until the voltage hits 1.72v, and gradually brightens until “snapping” to full brightness at 3.69v.

And that’s about it. Full procedure is available here.