Electronics · Reference card · Every mode of the meter · build 2026.09.23-1644
The idea
Every measurement is two probes touching two points. The dial decides what question you're asking — and each question has its own rules.
| Dial symbol | What it measures | The rule |
|---|---|---|
| V⎓ (straight lines) | DC volts — our setting | circuit powered ON; probes across two points |
| V~ (wavy line) | AC volts — wall-outlet electricity | not ours; see below |
| Ω | resistance | power OFF, part out of the circuit |
| 🔊 / ))) | continuity — the beep | power OFF |
| mA / A | current | red lead moves sockets; teacher at the table |
| ▸| diode & friends | diodes, capacitors, transistors | unlocked later in the course |
On many meters, several of these share a dial position and a SELECT button cycles the modes. The dial gets you to the neighborhood; the display's symbols tell you which mode is actually live — one more reason to read the display, not just the dial.
Dial to the continuity position — the sound symbol. On many meters, resistance, continuity, and diode test share one dial position, and a SELECT (or FUNC/MODE) button cycles between them; the mode is live when its symbol shows on the display. Touch the probes to two points: a beep means they're one unbroken conductor — the same node. Silence means they're not. This is the mode for testing wires end to end, mapping a breadboard, and settling arguments about what's connected to what.
Our class meters — AstroAI DM6000AR
Turn the dial to the shared Ω · beep · diode position, then press SELECT once — you're in continuity when the sound symbol appears on the display. The position wakes up in plain resistance, so lesson 4's Ω measurements need no button at all.
Unpowered only
Continuity (and ohms) work by pushing the meter's own tiny test current through the probes. Do it on a powered circuit and the supply's 5 V shoves back — the reading is garbage and the meter can be damaged. Supply off, or the part out of the circuit, every time.
Dial on Ω. Power off, the part out of the circuit, one probe on each leg. Measuring a part while it's still plugged in reads wrong — its neighbors offer the test current sneaky detours, and the meter can't tell which path it measured. And keep fingers off the metal: you're a resistor too, wired in parallel with whatever you're pinching.
The dial has two V positions. V⎓ — the V with straight lines — is DC: current that flows one steady direction. Everything we build is DC. V~ — the wavy V — is AC: current that reverses direction on a steady rhythm — 60 complete cycles each second — which is what house wiring carries. Wrong setting = nonsense readings, so check for the straight lines before you measure.
Volts are the one measurement made on a live, powered circuit: probes across two points, red on the side nearer +. (Backwards probes won't hurt anything — the reading just comes out negative.)
AC stays in the wall
The AC setting exists for electricians. Wall outlets and house wiring are off-limits with these meters and with everything else in this class: 120 V AC can be fatal. Nothing in our kits ever plugs a probe into a wall.
The meter picks its own scale and announces the choice in small letters at the edge of the display. The digits are meaningless until you've read them:
| Display says | It means |
|---|---|
| mV | millivolts — thousandths of a volt. 3.2 mV is basically zero. |
| V | plain volts. 3.2 V is a blue LED's whole voltage drop. |
| Ω | plain ohms. |
| kΩ | kilohms — thousands of ohms. 2.2 kΩ = 2,200 Ω. |
| MΩ | megohms — millions of ohms. Your hand-to-hand reading lives here. |
Same digits, three different components: 220 Ω, 220 kΩ, and 220 MΩ are a thousand and a million times apart. Glance at the unit before you write any number down.
Volts are measured across a part; current is measured through it. The meter can't watch current from outside the loop — it has to become part of the loop: break the circuit at one point and bridge the gap with the probes, so every bit of the flow passes through the meter.
On our meters that also means moving the red lead to a different socket — out of its home V/Ω jack, into the mA jack. The black lead never moves.
Why this mode kills meters
In current mode the meter is deliberately almost a plain wire, so it won't slow the flow it's measuring. That means: touch it across anything — the supply, a resistor, out of habit from volts mode — and you've built a short circuit straight through the meter. The internal fuse blows instantly, and the meter reads nothing in that mode until it's repaired. This is also why the red lead goes straight back to the V/Ω jack the moment you're done: a meter left wired for current is a trap for the next measurement. In class, the current jacks — mA and 10 A — stay off-limits unless a teacher is at the table.
The dial has more positions: a diode test (it can light an LED faintly and report its forward voltage), a capacitance setting for measuring capacitors, and on some meters a socket for checking transistors. They'll make sense once those parts join the kit — for now, just know the meter is ready when you are.