START A BITA circuit is a closed loop
Electricity only flows all the way round: out of one pin, through the parts, back into another. A gap anywhere opens the loop; a switch, a button or a touch closes it.
Wire game: the wire on P1, the loop on GND. When metal touches metal, the loop is closed and pin P1 is pressed is true.
Current only flows all the way round. Cut the loop anywhere, and it stops everywhere at once.
They all do the same thing: close the gap. Open again, and the current stops.
The wire on P1, the loop on GND. Metal touches metal: the loop closes, and pin P1 is pressed.
Nothing happens? Follow the loop from + round to −. Test each place until you find the gap.
A wire straight from + to − skips the parts. A huge current, heat. Never join + and − directly.
Every part sends its current back into GND. Many loops can share that one way back.
Volts (V) are the push, amps (A) are how much flows. More push through the same part: more flow.
Parts in a row share the push between them. The same current flows through every one of them.
Side by side, each part gets the whole push and its own current. The battery gives them all together.
A signal is a loop too. Two boards, or a board and a second battery, must join their GNDs.
More: why it works, and what stops it video
- The pin listens. Inside the Micro:bit a very weak pull keeps P1 "up". When P1 touches GND, the pin is pulled down, and the Micro:bit says pressed. Your finger on P1 and GND together works too, a little.
- Only metal that is bare. Paint, plastic coating and tape do not let electricity through. Sand the ends and use bare wire.
- Crocodile clips: one clip on the ring, the other on the metal. Check that the jaws bite on metal, not on insulation.
- Safe: the Micro:bit works with 3 V. You cannot feel it, and touching the wire is safe. But never join 3V and GND (or + and −) with a bare wire: that short cut gets hot.
| Micro:bit | Arduino | |
|---|---|---|
| the push | 3V ring: 3 V | 5V pin: 5 V |
| the way back | GND ring | GND pins (all joined inside) |
| a pin as a switch | pins.digital_write_pin(DigitalPin.P1, 1) | digitalWrite(9, HIGH); |
| a closed loop on a pin | input.pin_is_pressed(TouchPin.P1) | digitalRead(2) == LOW (with INPUT_PULLUP) |
No reaction? Follow the loop with your finger: pin, clip, wire, loop, clip, GND. Where is the gap?