6. Electronics Design - Max, Mckinnon, Oliver, and Yian

Oscilloscope - Max

This week, I will be testing a PWM LED with the oscilloscope. For the test, I will use a gumdrop LED, an Arduino, and some jumper wires. First, I connected the Oscilloscope’s alligator clips to a jumper cable, which I then connected to the positive and negative terminals of the already-wired LED, like this:

Then, I opened the Arduino IDE and wrote this script, using Pulse Width Modulation to control the brightness:

int ledPin = 3;
int pwm = 0;

void setup() {
pinMode(ledPin, OUTPUT);
}

void loop() {
while (pwm < 255) {
  if (pwm > 250){
    pwm = 0;
    }
  pwm += 1;
  analogWrite(ledPin, pwm);
  delay(15);
}
}

After running the script to fade the LED, I used the “Horizontal” knob to change the width of the viewing screen, to see finer details. I stopped at the “1 ms” setting. It looks like this:

You can see the square wave, and how the wave shifts to be “High” for more and more of the cycle as the pwm variable increases. This was really interesting, as I didnt really understand how PWM could change an LED’s brightness, but it makes sense now.

Analog Discover 2 - McKinnon Collins

First, I set up a simple LED Blink with an Arduino, this will be the circuit I will analyze.

I used this simple code to blink the LED. I had Microsoft Copilot generate it.

// External LED on pin 13
const int ledPin = 13;

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {
  digitalWrite(ledPin, HIGH);  // LED on
  delay(500);                  // wait 0.5 sec
  digitalWrite(ledPin, LOW);   // LED off
  delay(500);                  // wait 0.5 sec
}

Next I wired one of the many grounds on the Analog Discover to the Arduino’s ground. I then took 1+ and wired it to pin 13. Finally I took wire 0 and wired it to the same spot as 1+.

Here is the setup with the arduino and Analog Discovery 2.

Next I plugged the Analog Discovery 2 into my computer and downloaded WaveForms, the software used with the device. Once the software was installed, I clicked scope, then run, and then I could view the waveform.

Here is the graph where the blink is visible (The delay is high low delay is 0.5 seconds).

Multimeter Tests - Yian Hu

What is a Multimeter?

A Multimeter is a diagnostic tool used in engineering to measure key electrical properties in a circuit, including voltage (V), current (A), and resistance (Ω). Its purpose is to verify circuit operation, troubleshoot issues, and ensure components are functioning within safe limits. Voltage is measured in parallel across components, current is measured in series with the circuit path, and resistance is measured by testing how much a component opposes electrical flow. Many digital multimeters also include continuity and diode testing modes, making them essential tools for analyzing, debugging, and validating electronic systems.

Resistor Testing

The first test I conducted with the multimeter was a resistance test on a resistor. To do so, I utilized the ohm setting on my multimeter and pressed the probes against my resistor. The resistor ended up having a resistance of 384.8 ohms, a number very similar to its 383 ohm label. This tells me that the resistor is functioning and can be used in a circuit.

Voltage Testing

The second test I conducted with the multimeter was a voltage test on my XIAO RP2040. Since the microcontroller has both a 5V pin and a 3.3V pin, I wanted to see if it actually produced that much power. To conduct the test, I first plugged my XIAO RP2040 into a power source and switched my multimeter to the voltage setting (the one that say V, not mV). I then placed the black multimeter probe on the GND pin and the red probe on the 5V pin. The multimeter returned a value of 5.147 volts.

I then did the same thing with the 3V pin by moving the red probe to the pin. It returned a value of 3.307 volts.

Both pins returned a value that approximately matches their corresponding label. This allowed me to confirm that the microcontroller’s pins are functional and actually fulfill their supposed purpose.

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Capacitor Testing — Oliver Abbott

After observing the microcontroller circuit board’s behavior at the signal level with the oscilloscope and the Analog Discovery 2, I wanted to go a step further and verify the individual passive components that make those circuits work. Capacitors are one of the most common components on any circuit board, so I pulled a selection of electrolytic capacitors from our lab’s inventory and tested them with a multimeter to see how closely their actual capacitance matched their rated values.

What is a Capacitor?

A capacitor is a passive electronic component that stores electrical energy in an electric field between two conductive plates separated by an insulating material (dielectric). When voltage is applied, charge builds up on the plates. When the voltage source is removed, the capacitor can release that stored energy back into the circuit.

Capacitors are measured in Farads (F), but most practical capacitors are measured in microfarads (µF), nanofarads (nF), or picofarads (pF). They serve many purposes in circuits:

• Filtering — Smoothing out voltage fluctuations in power supplies
• Decoupling — Preventing noise from one part of a circuit from affecting another
• Timing — Working with resistors to create time delays (RC circuits)
• Energy storage — Providing short bursts of power when needed

Electrolytic Capacitors

For this test, I used electrolytic capacitors. These are polarized capacitors (they have a positive and negative lead) that use an electrolyte-soaked paper as the dielectric. They offer high capacitance values in a small package, making them common in power supply filtering and audio circuits. The voltage rating (e.g., 25V, 50V) indicates the maximum voltage the capacitor can safely handle.

Testing Process

I used a digital multimeter set to capacitance mode to measure each capacitor’s actual value and compare it to its rated value. Capacitors have a tolerance (typically ±20% for electrolytic), so some deviation from the rated value is expected.

Results

Rated Voltage	Rated Value (µF)	Tested Value (µF)	Deviation
25V	47	46.69	-0.66%
50V	1	1.151	+15.1%
25V	10	10.99	+9.9%
25V	220	237.1	+7.8%
50V	1000	948.7	-5.1%
25V	220	237.5	+8.0%
16V	470	479.3	+2.0%
16V	47	46.8	-0.4%
25V	470	447.2	-4.9%
16V	22	23.84	+8.4%
25V	220	218.9	-0.5%
16V	33	39.47	+19.6%
50V	3.3	3.655	+10.8%
25V	22	23.12	+5.1%

Analysis

All 14 capacitors tested within the standard ±20% tolerance for electrolytic capacitors. A few observations:

• Most accurate: The 16V 47µF capacitor measured 46.8µF, only -0.4% off its rated value
• Least accurate: The 16V 33µF capacitor measured 39.47µF, +19.6% above its rated value — still within tolerance but close to the limit
• General trend: Lower capacitance values (1µF, 3.3µF) tended to show higher percentage deviations, which is typical since small manufacturing variations have a larger relative impact on smaller values
• Consistency: The two 25V 220µF capacitors measured 237.1µF and 237.5µF respectively, showing good consistency between components of the same rating

This exercise demonstrates why it’s important to measure components before using them in precision circuits — the rated value is a nominal target, not an exact guarantee.

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Last update: March 5, 2026