pxt-calliope/docs/reference/input/on-pin-pressed.md
2016-06-11 22:28:57 -04:00

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# On Pin Pressed
Start an [event handler](/reference/event-handler) (part of the program
that will run when something happens, like when a button is pressed).
This handler works when you press pin `0`, `1`, or `2` together with `GND`.
When you are using this function in a web browser, click the pins on the screen instead of the ones
on the BBC micro:bit.
If you hold the `GND` pin with one hand and touch pin `0`, `1`, or `2` with the other,
a very small (safe) amount of electricity will flow through your body and back into
the micro:bit. This is called **completing a circuit**. It's like you're a big wire!
```sig
input.onPinPressed(TouchPin.P0, () => {
})
```
## ~hint
This function works best when the BBC micro:bit is using batteries for power,
instead of the USB cable.
## ~
### Example: pin pressed counter
This program counts how many times you press the `P0` pin.
Every time you press the pin, the program shows the number of times on the screen.
```blocks
let count = 0
basic.showNumber(count, 100)
input.onPinPressed(TouchPin.P0, () => {
count = count + 1
basic.showNumber(count, 100)
})
```
### See also
[BBC micro:bit pins](/device/pins), [pin is pressed](/reference/input/pin-is-pressed), [analog read pin](/reference/pins/analog-read-pin), [analog write pin](/reference/pins/analog-write-pin), [digital read pin](/reference/pins/digital-read-pin), [digital write pin](/reference/pins/digital-write-pin)