In this lab, I explored the properties of electricity with a digital multimeter.

CONTINUITY – Measuring Continuity
I turned my multimeter dial to the continuity mark in order to measure the continuity between two points on a switch. When the switch is open, there is no continuity because there is no electricity flow. When the switch is closed, there is continuity (“beep”) since there is electricity flowing through the switch. When I measured continuity between two wires on my breadboard, I only heard a “beep” when the wires were placed along the same row and not when the wires were placed along the same column, which tells me that the rows on a breadboard are connected underneath, but the columns are not connected.

VOLTAGE – Measuring Voltage of an LED
I built a breadboard circuit by wiring a 7805 5V regulator, a red LED, and a 220-ohm resistor. When I tested the DC voltage of the LED by putting the multimeter probes on the two ends of the LED, I got a reading of 1.75 volts.  I concluded that the resistor must be using the remaining 3 volts from the circuit.

Basic LED circuit

VOLTAGE – A Basic LED Circuit
I added a push-button switch to my breadboard circuit, and I measured the voltage of each component before and after I pressed the switch. When the switch was unpressed (open), I got a reading of 3.64 volts from the switch, and both the resistor and LED measured 0 volts. When I pressed the switch (closed), the flow of electricity went through the resistor and LED, so I got a reading of 0 volts from the switch, and 1.85 volts from the LED, and 1.42 volts from the resistor. The total resistance across all components equals 5.03 volts, but the LED plus resistor equals 3.27 volts, so I am losing 1.76 volts in the circuit which is probably being converted to heat, light, and other forms of energy.

Basic LED circuit with push-button switch

VOLTAGE & RESISTANCE – Components in Series

I added two red LEDs in series on the breadboard, and measured the resistance of each component when I pressed the switch (closed).  The first LED measures 1.69 volts, the second LED measures 1.77 volts, and the 220-ohm resistor measures .85 volts.  Therefore, the total resistance of all the components is 4.31 volts, so there is .69 volts converted to heat or lost energy somewhere due to a slightly inefficient circuit.  When I tried to add a third LED in series, it did not light up because there isn’t enough voltage flowing across the circuit to light up all of the LEDs.

Two red LEDs in series on breadboard

VOLTAGE & RESISTANCE – Components in Parallel

I wired three red LEDs in parallel on the breadboard along the same rows, and measured the voltage across each LED — each LED measures 1.57 volts.  Unlike the LEDs placed in series, these LEDs all measure the same voltage because they are placed in parallel in the circuit.

Three red LEDs in parallel on breadboard

Three LEDs lit up in parallel on breadboard

AMPERAGE – Measuring Amperage of LEDs in Parallel

In order to measure amperage of these LEDs in parallel, I moved my multimeter’s red lead from the “mA” port to the “10A” port, and turned my multimeter dial to the Amperage mark.  Then, I removed the anode leg of one of the LEDs from the series, and I placed the multimeter leads on the “open holes” in order to complete the circuit, so that the amperage flowing through the circuit would show up the same on the multimeter as it is in the LEDs.

VOLTAGE – Generating Variable Voltage with a Potentiometer

I soldered three hook-up wires to the potentiometer’s three leads.  On my breadboard, I connected a 220-ohm resistor and a red LED, and connected these two components to the potentiometer.  As I turned the knob of the potentiometer, the LED brightened!  With a slight turn, the LED measures 1.61 volts.  Then, as I turn the pot knob, the LED measures 1.65 volts.  At its maximum voltage, the LED measures 1.84 volts.  The resistor protects the LED from the potentiometer’s 5 volt lead when it has zero resistance.

Turning potentiometer dial on breadboard to brighten LED

If I put the multimeter’s leads on ground and the resistor (side closest to pot), then I am able to see the full range of voltage increasing and decreasing as I turn the knob because the pot is acting as a voltage divider.


2 Responses to “Lab – Electronics”  

  1. 1 Avadhut Deshmukh

    6. Generating a Variable Voltage with a Potentiometer

    how to make (3 led, 3 potentiometers) please help me ,send me schematic diagram ?

  2. 2 suzkita

    For a schematic of a potentiometer and LED (also 3 LEDs), check out the lab exercise on our Physical Computing class page: http://itp.nyu.edu/physcomp/Labs/Electronics#toc8
    Potentiometer schematic:
    http://itp.nyu.edu/physcomp/uploads/breadboard_LED_pot.png

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