Notes / Test & Debug Instruments
Multimeter: the first instrument you reach for
Voltage, current, resistance, continuity. And the common mistake that blows the fuse when measuring current.
Basic measurements
| Mode | How to connect | Use |
|---|---|---|
| Voltage (V) | In parallel across the two points | Checking supplies, pin levels |
| Current (A) | Break the circuit and connect in series | Current consumption |
| Resistance (Ω) | Power off, across the part | Resistor values, open circuits |
| Continuity (beep) | Power off, two points | Solder bridges, checking wiring |
| Diode | Power off | Checking Vf, a MOSFET's body diode |
The current-measurement mistake
Touch the probes across a supply while still in current mode and the multimeter is a short circuit: the fuse blows or the board is damaged. Make a habit of moving the probe back to the voltage jack when you finish.
The internal shunt resistor in current mode means the measurement itself drops voltage (burden voltage). For µA measurements on a low-power MCU, a dedicated instrument (a current profiler) is accurate.
RoadmapSee where this note sits in Test & Debug Instruments→Order for first power-up
- Before applying power, measure the VCC-GND resistance → a few ohms or less suggests a short
- Apply power from a supply with a current limit set
- Check the output voltage of each regulator
- Then load the firmware
When choosing one
Look for true RMS (needed for non-sinusoidal waveforms such as PWM), auto-ranging, and the CAT rating (the safety category for high-voltage work).