Week06 Adults¶
Group Assignment: Test Equipment¶
This week we were tasked with using the test equipment in our lab to observe the operation of an embedded microcontroller circuit. We tested three pieces of equipment: a multimeter, an oscilloscope, and a logic analyzer.
Multimeter¶
Building the Test Circuit¶
Camille and Kim built a blinking LED on a breadboard using an ESP32-C6.
The LED blinks after some troubleshooting
They were having trouble getting the LED to blink, so all four of us took a minute to analyze the board.
Testing the LED¶
Angela and Kim used the multimeter to test the LED to make sure it was not dead. Using the multimeters we were given for home, we were able to get the LED to light up. We also tested with a more advanced meter from the lab and were able to get it to light up and read a forward voltage of 1.8V.
How to Test an LED with a Multimeter¶
Diode Test Mode (preferred):
- Set your multimeter to the diode symbol
- Connect red probe to the anode (longer leg, +) and black probe to the cathode (shorter leg, −)
- A good LED will show a forward voltage reading (typically 1.8V–3.3V depending on color) and may glow faintly
- Reverse the probes — you should get OL (overload/no reading), which is correct
- A dead LED will show OL in both directions
Quick reference for forward voltage by color:
| LED Color | Forward Voltage |
|---|---|
| Red/Yellow | ~1.8–2.2V |
| Green | ~2.0–2.4V |
| Blue/White | ~2.8–3.3V |
Debugging the Circuit¶
After making sure the LED was good, we went back to the breadboard. Angela counted the location of the pins and Kim compared the pins to the board diagram — we realized we had the resistor on pin 22, not pin 21 like we had thought. We moved the resistor to pin 21 and we had a working blinking LED!
Measuring Voltage¶
As a group we used the multimeter to measure the voltage of the blinking LED. Dorian held the meter leads to the LED and we read the meter changes. When the LED was off, the voltage dropped to zero; as it turned on, it rose to about 3V.
Measuring Current (Amperage)¶
We continued to test the meter capabilities by measuring the current through the LED. We tested with both the lab meter and our home meters.
HOME METER
LAB METER
Kim, then Camille, both took a turn holding the meter leads between the LED and the resistor. Dorian assisted with checking the circuit design and Angela helped with the settings on the multimeters. At first we could get the LED to light up, but on the home meters we could not get a current reading. We tried on the lab meter and were able to get a reading on the first try.
Our reading bounced around a lot — we realized we were still using the blinking LED code. Kim switched the code and flashed the board with a solid (always-on) LED program. We checked again and received a measurement of approximately 3.8mA using the lab meter.
Verifying with Ohm’s Law¶
Dorian and Angela calculated Ohm’s Law to compare our measured values to our expected values. Dorian realized we had not measured the resistance we needed for our calculations, so we went back to the board. She measured the voltage drop over the resistor as 1.27V. Kim and Camille measured the voltage over the diode and got 1.9V.
| Value | Measurement |
|---|---|
| V (across resistor) | 1.27V |
| R (measured) | 327 ohms |
| I (calculated) | 3.8mA |
| I (measured on meter) | ~3.8mA |
Our calculated value matched exactly what we measured on the meter.
Resistor Color Band Verification¶
The 383 ohms label was the bin we pulled the resistor out of, but it was not actually a 383 ohms resistor. We measured it with the meter and also used the color band chart to confirm. The resistor bands were orange, orange, blue, black, gray, which reads as 336 ohms ±0.05%. We read 327 ohms on our multimeter, which falls within tolerance.
Oscilloscope¶
Overview¶
During this portion of the lab, the team explored using an oscilloscope to visualize electrical signals from a microcontroller circuit. Camille set up her laptop to run the keyestudio board that the student group had configured with a slow blinking LED. We experimented with both digital (PWM) and analog outputs driving an LED, adjusting code parameters in real time and observing how the waveform changed on the oscilloscope display.
Oscilloscope Basics¶
Voltage Scale (Vertical Knob): Adjusting the vertical dial changes the volts-per-division on the display. This doesn’t alter the actual signal — it’s like zooming in and out on the measurement, similar to switching a multimeter between voltage ranges. If a signal is very small, you can “zoom in” by lowering the volts/div setting to see more detail.
Measurement Fundamentals:
- Voltage is measured in parallel with the component
- Current is measured in series with the component
Reading the Waveform: Dorian explained the high part of the waveform represents high voltage (LED on/bright), and the low part represents low voltage (LED off/dim). One full cycle is the sum of the high and low portions together.
PWM vs. Analog Signals¶
Square Wave (Digital / PWM): With PWM, the signal switches between 0V and 5V — nothing in between. The duty cycle (ratio of on-time to off-time) controls the perceived LED brightness: a longer on-time means a brighter LED. We were able to get a clean square wave on the oscilloscope without much difficulty.
- Digital: square wave PWM is a digital switching signal with abrupt transitions, having only two voltage states: high and low
- Analog: sine wave represents a smooth, continuous variation in voltage
Analog Fade: When running code that fades an LED in and out (ramping brightness up then down), the oscilloscope showed a different, more gradual waveform pattern. We adjusted delay values in the code and observed how the waveform timing changed accordingly on screen.
Code Parameter Experiments¶
We experimented with different delay values to see how they affected the waveform:
| Delay Setting | Effect on Waveform |
|---|---|
| 50–100ms | Fast blinking, much easier to capture on the scope |
| 1000ms (1s) pause | Visible flat period on the waveform between transitions |
| 5000ms (5s) pause | Very long off period — extremely hard to find the signal on the scope |
| Fade (0–100 ramp) | Visible ramp-up and ramp-down slopes on the display |
Troubleshooting Observations¶
Pin Selection Matters: Initially the code was writing to a digital pin instead of a PWM-capable pin, which produced unexpected results. Angela and Camille switched to the correct PWM pin was necessary to see the expected analog-style waveform.
Finding the Signal: When the LED had a long off-delay (e.g., 5 seconds at 0V), it was very difficult to locate the signal on the oscilloscope. The solution was to make the blink rate much faster so the waveform would repeat frequently enough to capture.
Noise at High Zoom: When Angela zoomed in to the millivolt range (~20mV to -16mV), we observed noise rather than a meaningful signal. This is expected behavior — at very small voltage scales, electrical noise from the system and environment becomes visible.
Key Takeaway¶
Angela explained that if you know what the expected waveform should look like (square wave for PWM, ramp for analog fade, sine wave for AC, etc.), you can compare it to what the oscilloscope actually displays. The oscilloscope won’t tell you where the problem is, but it shows you what is happening electrically — which helps narrow down whether the issue is in your code, your wiring, or your components.
Logic Analyzer¶
Overview¶
For this portion, we worked with the logic analyzer Analog Discovery 2 to capture signals from the blinking LED circuit with a resistor and eventually a capacitor. We had remote help (Angela’s wonderful dad) via phone/video call guiding the process.
Pinout for the Analog Discover 2
Phase 1 — Initial Setup¶
Camille decided to do a quick self-test using the oscilloscope function in WaveForms as a starting point. She was able to get a nice sine wave with that self-test.
Angela and Camille moved on to connecting the logic analyzer to the circuit with the LED. It was visibly blinking on the circuit but nothing was showing on the logic analyzer. The first challenge was figuring out the time base — it was set too wide to see the signal. We weren’t sure about the correct time division setting, eventually working toward 1 second/division before adjusting further.
Phase 2 — Identifying the Correct Probe Wire¶
The logic analyzer has many probe wires and we struggled to figure out which probe corresponded to which channel. There was confusion between Channel 0, Channel 1, and the Trigger (T1) wire. After trial and error — plugging in different wires to the resistor on the circuit — we identified that the T1 (Trigger 1) wire, was the correct one to use. Plugging the Channel 0 wire in first showed nothing.
Phase 3 — Getting the First Signal¶
After connecting T1, nothing was visible because the time base still needed adjusting. Angela’s dad suggested reducing it from 1 second/division down to 100 milliseconds (0.1s) per division. We also explored the sample rate (8 kHz) and position settings. Eventually the first signal appeared — a visible square wave on the orange trace (Channel 1/T1) showing the LED’s on/off cycle after we discovered we needed to hit the Scan button.
Phase 4 — Finding the Second Channel¶
The blue trace (Channel 2) was picking up something intermittent. Through a hands-on process, Camille started touching individual wires one at a time. We discovered it was responding to her physically touching probe wires — picking up body noise. After systematic testing, the V+/2+ pin was identified as the live signal source for Channel 2. Connecting that probe to the circuit produced a second visible waveform on the blue channel.
Phase 5 — Adding a Capacitor¶
Angela’s dad suggested placing a capacitor between T1 and the V+ (2+) probe points on the circuit. Using a 10 microfarad capacitor, we connected it and observed the capacitor charge and discharge curve — a smooth ramp up and down instead of a sharp square wave. This demonstrated the RC charging behavior in both directions.
Phase 6 — Wrap-Up¶
We zoomed in and out on the time base to see the waveform at different scales, confirming we could view a full on/off cycle. In summary, we accomplished:
- Found the correct probe wire (T1) for Channel 1
- Adjusted the time base to see the square wave from the LED blinking circuit
- Identified the blue channel’s live wire (V+/2+) by touch-testing
- Added a capacitor to observe charge/discharge behavior
Files¶
- Fade Oscilloscope code: fade_oscillascope.ino
- Sine Wave: sin_wave_usingVoltage.ino