September 8, 2020

Lab: Electronics

In this lab I reviewed the basic functions of a multi-meter then created a few circuits using LEDs, resistors, buttons and a potentiometer.

Making my way through the settings on the multimeter I started with the diode continuity function.

Digital multimeter reading open circuit — Keeping the multimeter probes apart in the continuity function results in an “Open” reading.

Digital multimeter reading short circuit — Keeping the multimeter probes apart in the continuity function results in an “Open” reading.

Holding the multimeter probes apart my multimeter read “OPEn” indicating that the circuit is open and there is no flow of electrons. Touching the probes together the screen read “Shrt” for short, indicating a closed circuit where electrons flow with no resistance.

Multimeter measuring resistance — Switching to measure resistance with the multimeter without touching the probes results in a reading of 0 ohms.

A finger touching probes on multimeter — Switching to measure resistance with the multimeter without touching the probes results in a reading of 0 ohms.

Next I measured resistance with an open circuit, then using my finger as a conductor. My multimeter is auto ranging so it automatically scales the reading to the nearest whole unit. In the case of my skin the resistance reading was 2.949 milliohms.

Next I setup a breadboard to take voltage readings at various points in the circuit.

Red LED lit on a breadboard — I have setup and powered a basic 5-volt circuit with a red LED and 220ohm resistor.

Multimeter probes reading 5.058 volts on a circuit board with red LED — I have setup and powered a basic 5-volt circuit with a red LED and 220ohm resistor.

The circuit voltage, due to the 7805 voltage regulator, is approximately 5 volts. Using the probes to measure the voltage drop across the red LED the reading is 1.915 volts. This “loss” of energy is accounted for by light and heat emitted from the LED.

My brindle rescue dog Cooper — Quick break with my dog Cooper.

Had to take a quick dog break! My dog Cooper was patiently waiting for a walk. He is a very good boy.

Ok, back from a walk and time to add a few more components to the board.

Breadboard with red LED and pushbutton — Adding a pushbutton switch to the circuit results in a naturally open or “off” position.

Finger pushing button on breadboard with lit red LED — Adding a pushbutton switch to the circuit results in a naturally open or “off” position.

A pushbutton switch!

Multimeter reading 3.716 volts across a pushbutton on a breadboard — Reading the voltage across the pushbutton reads 3.716 volts

Multimeter reading 9.9 millivolts across a push button on a breadboard — Reading the voltage across the pushbutton reads 3.716 volts

Reading the voltage drop across a few different components and points on the board I find that strangely there is a 9.9 millivolt voltage drop across the pushbutton switch. This will seem more relevant later…

Next I expand the circuit to include an additional red LED in series.

Pressing the pushbutton both LEDs turn on as expected.

I continued to measure the voltage drop around the circuit. A drop of 1.3 volts across the resistor, 1.85 volts across each of the matching red LEDs, and the board total voltage of 5 volts. 1.3 + 1.85 + 1.85 = 5, all of the electrons are accounted for. Importantly the voltage drop for the two LEDs is now less than a single LED which was 1.9 volts. Looks like we’re running out of power.

Adding a third smaller LED they were noticeably dimmer. The voltage drop of three LEDs is too much.

Next I rearranged the components and ran three LEDs in parallel. Interestingly they all light! This configuration is much better than running them all in series, which reminds me of the WS2812 LED strips I have used in the past that also supplies power in parallel.