Group assignment: Use the test equipment in your lab to observe the operation of an embedded microcontroller#

For this assignment I used the Multicomp PRO MP720780 handheld oscilloscope/multimeter to observe the output of an RP2040-based circuit that blinks three LEDs in succession. I measured the output pin of one of the LEDs (positive lead on the RP2040 output, negative lead on ground).

Voltmeter measurements#

I started by using the device in voltmeter (DCV) mode to measure the voltage across the LED output pin.

When the LED was on, the voltmeter read approximately 1.3V DC on the 2V range, this is the voltage drop across the LED

Voltmeter reading approximately 1.3V DC when the LED is on

When the LED was off, the reading dropped to 0V as expected, confirming the RP2040 output pin was low

Voltmeter reading 0V when the LED is off

Oscilloscope measurements#

Next I switched the device to oscilloscope mode to try and capture the blinking waveform. I connected the probes to the same LED output pin and ground.

Initially I got a flat line on the display with a 500us time base and 1.00V vertical scale. the time base was too fast to see the slow LED blink cycle

Oscilloscope showing a flat line at 500us time base, too fast to capture the slow LED blink

I then explored the different settings. Here you can see the bottom status bar showing the channel scales (200mV, 100mV) and the sample rate of 250Sa/s

Close-up of oscilloscope status bar showing 200mV and 100mV scales with 250Sa/s sample rate

I tried changing the CH1 coupling to AC mode with the probe set to 10X to see if that would help pick up the signal

CH1 settings showing AC coupling with 10X probe and full bandwidth

Then I switched back to DC coupling with the probe at 1X, which is more appropriate for a DC on/off signal like the LED blink

CH1 settings showing DC coupling with 1X probe and full bandwidth

I also tried the single trigger type to attempt to capture a single transition of the LED turning on or off

CH1 settings showing DC coupling with single trigger type

Here is the oscilloscope with the probes connected, showing some activity on the display. The yellow trace shows a mostly flat line with some noise, I wasn’t able to clearly capture the square wave of the blinking LED during this session

Oscilloscope with probes connected showing signal activity on the display

Reflections#

I was able to confirm the LED output voltage with the voltmeter (about 1.3V when on, 0V when off), but I wasn’t able to capture a clean square wave on the oscilloscope. The LED blink cycle was likely too slow for the default oscilloscope time base settings, and I would need to adjust the horizontal time base to a much longer period (seconds rather than microseconds) to capture it. This is something I’d like to revisit later with a faster-switching signal or with the correct time base configuration.