A digital multimeter (DMM) measures voltage, current and resistance.
| To measure | Dial setting | How to connect | Circuit power |
|---|---|---|---|
| DC voltage | V with a straight line | In parallel across the component | ON |
| AC voltage | V with a wave | In parallel | ON |
| Current | A (or mA) | In series (break the circuit and insert the meter) | ON |
| Resistance | Ω | Across the component, removed from circuit | OFF |
| Continuity | Diode or buzzer symbol | Across the path; beeps if connected | OFF |
Rules: red lead to the positive side, black lead to COM. Start with the highest range if the meter is not auto-ranging. Move the red lead to the current socket only when measuring current, and move it back afterwards, because measuring voltage with the lead in the current socket can blow the fuse.
Try it 1.1. Build a 5 V supply from the Arduino 5V pin, a 220 Ω resistor and an LED in series. Measure (a) the voltage across the resistor, (b) the voltage across the LED, (c) the current. Check that (a) + (b) equals 5 V and that Ohm's law gives the same current.