Measurement Instruments
When a circuit "doesn't work," these tools tell you what's actually happening instead of guessing. Pick the instrument that matches the question.
| Question | Instrument |
|---|---|
| Is the voltage / continuity / resistance right? | Multimeter |
| What does this analog signal look like over time? | Oscilloscope |
| What are these digital bus lines doing (I²C/SPI/UART)? | Logic analyzer |
Multimeter (DMM)​
The first tool you reach for. Measures DC/AC voltage, current, resistance, continuity, and often diode/capacitance.
- Voltage: probes in parallel with the point you're measuring (red to the node, black to GND).
- Continuity: the beeper confirms two points are connected — perfect for finding shorts and broken traces with the power off.
To measure current you move the red lead to the A/mA jack and put the meter in series with the load. If you leave it in the current jack and then probe a voltage, you create a near short. Always return the lead to the VΩ jack when done.
Oscilloscope​
Shows voltage as a waveform over time — essential for analog signals, PWM, edges, noise, and timing.
- Match the probe attenuation (often 10×) to the channel setting, or every reading is off by 10×.
- Always connect the probe ground clip to circuit ground.
- Set trigger, timebase (horizontal) and volts/div (vertical) so the waveform is stable and fills the screen.
A bench scope's probe ground is tied to earth ground. Clipping it to a non-ground node (or probing mains-referenced circuits) can short through the scope and damage your board or the instrument. Know where your ground is before you clip.
Logic analyzer​
Captures many digital lines at once and decodes protocols (I²C, SPI, UART, etc.). The right tool for "is the sensor actually replying on the bus?" — it shows the decoded bytes, not just the voltage.
Use a scope to judge signal quality (is the edge clean, is there ringing?). Use a logic analyzer to judge protocol correctness (are the right bytes on the bus at the right time?). For embedded bus debugging, the logic analyzer is usually faster.
These instruments pair naturally with the Programmers & Debuggers: the debugger tells you what the code thinks it's doing; the scope/analyzer tells you what the pins are really doing. The bug is often the gap between the two.