Lab 3: Measuring Voltage

Posted September 28th, 2009 in ITP and tagged Physical Computing by Cindy

For this lab session, we had to familiarize ourselves with the multimeter in testing electrical setup for parallel and serial circuit layout.

#1 Disclaimer: If you sense heat, smoke, or an extremely glowing LED, DO NOT touch the voltage regulator. Disconnect power ASAP. I learned the hard way and burned my finger by accidentally touching the voltage regulator. Plus I kinda melted the plastic hole peg on my breadboard… So, kids, please make sure your breadboard is set up properly. See my chart below.

Meet the Voltage Regulator (above) – look at the 3 prongs — remember IGO (Input, Ground, Output).

#2 Disclaimer: The D/C Jack connects to the D/C Power adapter which is not PICTURED in the lab wiki that Tom Igoe outlines here. That should be included in your tool kit if you purchased it from the NYU bookstore.

Measuring Voltage

First, I measured the voltage between the power and ground bus rows on the breadboard on both ends. I reached close to 5V but not quite, more like 4.63-4.64V. It’s a good practice to make sure your breadboard is wired properly. If you measure your black point to the metal tab of the voltage regulator and take your red point to the power grid, you should get a reading close to 15V.

Measuring Voltage on Basic LED Circuit (On/Off)

In the OFF position, the button switch, itself, measured 3.65V on the multimeter. However, the LED registered no electricity. While the switch was ON, the multimeter had readings. I measured the voltage across the LED and the resistor as well. While ON, the LED had a 1.77V reading. The Resistor read 2.97V.

The total resistance across all the components did add up (roughly) to the voltage between power and ground on your board.

Resistor Reading. = 2.97V

LED = 1.77V

Components in Series

Here’s the Breadboard Setup.

Measuring TWO LEDs

While ON, the Multimeter read each LED as 1.77V, 1.77.

The Resistor readings = 1.35. The Total with the Resistor and 2 LED readings = 4.89

Measuring Three LEDs

Here’s the Components laid out in Series.

While ON, the Top LED = 1.68V, Middle LED = 1.68V, Bottom = 1.72V. Resistor = 1.38, Total = 6.48

Step 5. Components in parallel; measuring amperage

See how I left 1 LED unlit and off-set from the powered grid? That’s because I’m taking my multimeter and connecting the unlit LED to the electrical grid. The multimeter is set to measure amperage. The off-set LED measured at 2.74amperage.

Make sure that you check which holes your leads are connected to when you’re using a meter. Measuring amperage with the red lead in the voltage hole, or measuring voltage with it in the amperage holes is a good way to damage the meter????

Step 6: Generating a Variable Voltage with a Potentiometer

I generated changing voltage using a potentiometer. Cranked at full tilt, the pentiometer is still controlling the voltage reaching the LED at slightly under 5V.