---
title: "Controlling a GPIO input/output pin"
weight: 10
---
# Controlling a GPIO input/output pin
In this guide, we are using [periph.io](https://periph.io/), a library for
peripheral I/O in Go, to set one of the Raspberry Pi’s General Purpose I/O
(GPIO) pins to a logical high (3.3V) or low (0V) signal.
periph.io supports the Raspberry Pi 3 and Raspberry Pi 4, starting with version
`v3.6.4`.
## Connect GPIO pins based on pinout
To verify the code is doing what we expect, let’s connect a multimeter as per
[pinout.xyz](https://pinout.xyz)’s pinout:
* pin number 18 (signal `BCM24`, labeled `24` in the pinout above)
* pin number 20 (signal `GND`)
We need to set the multimeter to “Voltage measurement, DC (direct current)”.
## Setting an output pin signal
To set the pin high and low, alternatingly, with a 5 second frequency, we will
be using the `hello-gpio` program, which is a slightly modified version of the
example at [periph.io/device/led](https://periph.io/device/led/):
```go
package main
import (
"log"
"time"
"periph.io/x/periph/conn/gpio"
"periph.io/x/periph/host"
"periph.io/x/periph/host/rpi"
)
func doGPIO() error {
log.Printf("Loading periph.io drivers")
// Load periph.io drivers:
if _, err := host.Init(); err != nil {
return err
}
log.Printf("Toggling GPIO forever")
t := time.NewTicker(5 * time.Second)
for l := gpio.Low; ; l = !l {
log.Printf("setting GPIO pin number 18 (signal BCM24) to %v", l)
// Lookup a pin by its location on the board:
if err := rpi.P1_18.Out(l); err != nil {
return err
}
<-t.C
}
return nil
}
func main() {
if err := doGPIO(); err != nil {
log.Fatal(err)
}
}
```
Install the program on your Raspberry Pi using gokrazy (see [Quickstart](/quickstart/)):
```shell
gokr-packer \
-update=yes \
github.com/gokrazy/hello \
github.com/gokrazy/breakglass \
github.com/gokrazy/serial-busybox \
github.com/gokrazy/hello-gpio
```
…and wait a few seconds for it to reboot.
At this point, we should be able to see the high/low signal on the multimeter,
alternating between 3.3V (high) and 0V (low) every 5 seconds:
