Multimeter benutzen
A multimeter is the single most important debugging tool on your bench. It measures voltage, resistance, continuity, and (sometimes) current.
Which Multimeter
| Model | Price | Best For |
|---|---|---|
| Uni-T UT61E | ~$50 | Best value, accurate, data logging |
| Aneng AN8008 | ~$25 | Compact, auto-ranging, good starter |
| Fluke 117 | ~$200 | Professional, lifetime accuracy |
| Harbor Freight freebie | ~$0 | Barely usable — but better than nothing |
What to Measure
Continuity (Beep Mode)
Tests if two points are electrically connected. Most-used function.
- Switch to Ω/continuity mode (symbol: →+ or sound wave)
- Touch probes together → should beep
- Touch probes to two points → beep = connected
- Use to: check solder joints, trace PCB traces, verify wires are not broken
DC Voltage
- Switch to V⎓ (DC voltage), pick range above expected voltage
- Red probe to positive, black to ground
- Read display
- Use to: check battery level, verify GPIO output, find short circuits
Current measurement is different
To measure current, you must move the red probe to a separate jack (marked A or mA) and put the meter IN SERIES with the circuit. Most blown multimeter fuses come from trying to measure voltage with probes in the current jack.
Quick Diagnosis Flow
Board not working?
├── Measure VCC → GND. Expected voltage? (3.3V? 5V?)
│ └── No → Power supply issue or short circuit
├── Measure GPIO output. HIGH = VCC? LOW = 0V?
│ └── Wrong → GPIO pin damaged or wrong pinMode
├── Continuity test each solder joint
│ └── No beep → cold joint, reflow
└── Check for shorts between adjacent pins (NO beep expected)
└── Beep → solder bridge, clean with wick
Common Mistakes
| Mistake | Consequence | How to Avoid |
|---|---|---|
| Probes in current jack while measuring voltage | Blown fuse (or blown meter) | Always return red probe to V/Ω jack |
| Wrong range selected | Display shows "1" or "OL" (overload) | Use auto-ranging meter or start high |
| Measuring resistance with power on | Wrong reading, may damage meter | Power off circuit first |
| Probes touching each other | Short circuit | Keep probe tips apart |