1ec8cbf7d9
related to https://github.com/google/periph/issues/432 fixes https://github.com/gokrazy/gokrazy/issues/33
89 lines
2.5 KiB
Markdown
89 lines
2.5 KiB
Markdown
---
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title: "Controlling a GPIO input/output pin"
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weight: 10
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---
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# Controlling a GPIO input/output pin
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In this guide, we are using [periph.io](https://periph.io/), a library for
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peripheral I/O in Go, to set one of the Raspberry Pi’s General Purpose I/O
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(GPIO) pins to a logical high (3.3V) or low (0V) signal.
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periph.io supports the Raspberry Pi 3 and Raspberry Pi 4, starting with version
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`v3.6.4`.
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## Connect GPIO pins based on pinout
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<a href="https://pinout.xyz"><img src="/img/raspberry-pi-pinout.png" width="700" align="right" style="border: 1px solid grey; margin-bottom: 2em; margin-top: 1em"></a>
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To verify the code is doing what we expect, let’s connect a multimeter as per
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[pinout.xyz](https://pinout.xyz)’s pinout:
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* pin number 18 (signal `BCM24`, labeled `24` in the pinout above)
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* pin number 20 (signal `GND`)
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We need to set the multimeter to “Voltage measurement, DC (direct current)”.
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## Setting an output pin signal
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To set the pin high and low, alternatingly, with a 5 second frequency, we will
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be using the `hello-gpio` program, which is a slightly modified version of the
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example at [periph.io/device/led](https://periph.io/device/led/):
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```go
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package main
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import (
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"log"
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"time"
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"periph.io/x/periph/conn/gpio"
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"periph.io/x/periph/host"
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"periph.io/x/periph/host/rpi"
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)
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func doGPIO() error {
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log.Printf("Loading periph.io drivers")
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// Load periph.io drivers:
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if _, err := host.Init(); err != nil {
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return err
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}
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log.Printf("Toggling GPIO forever")
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t := time.NewTicker(5 * time.Second)
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for l := gpio.Low; ; l = !l {
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log.Printf("setting GPIO pin number 18 (signal BCM24) to %v", l)
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// Lookup a pin by its location on the board:
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if err := rpi.P1_18.Out(l); err != nil {
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return err
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}
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<-t.C
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}
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return nil
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}
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func main() {
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if err := doGPIO(); err != nil {
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log.Fatal(err)
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}
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}
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```
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Install the program on your Raspberry Pi using gokrazy (see [Quickstart](/quickstart/)):
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```shell
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gokr-packer \
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-update=yes \
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github.com/gokrazy/hello \
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github.com/gokrazy/breakglass \
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github.com/gokrazy/serial-busybox \
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github.com/gokrazy/hello-gpio
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```
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…and wait a few seconds for it to reboot.
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At this point, we should be able to see the high/low signal on the multimeter,
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alternating between 3.3V (high) and 0V (low) every 5 seconds:
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<a href="/img/2020-06-15-gpio.jpg"><img src="/img/2020-06-15-gpio.thumb.jpg" srcset="/img/2020-06-15-gpio.thumb.2x.jpg 2x,/img/2020-06-15-gpio.thumb.3x.jpg 3x" width="700" style="border: 1px solid grey; margin-bottom: 2em; margin-top: 1em"></a>
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