Experimenting blinking an LED with Gobot and Raspberry Pi

In the post 'Playing with Gobot on a Raspberry Pi', I got a Go program running on a Raspberry Pi. In this post, I am going to continue experimenting with different ways to use the Gobot framework to flash a LED.

Experiment - blink multiple sequences

In this experiment, I want to flash the LED three times rapidly then blink the LED continuously.

I created two functions. The first function flashes a LED rapidly three times. To accomplish this, I used a for loop and the sleep function. The second function flashed the LED every second. The 'work' variable calls the two new functions.

Here is the code

	package main
	import (
	"time"
	"gobot.io/x/gobot"
	"gobot.io/x/gobot/drivers/gpio"
	"gobot.io/x/gobot/platforms/raspi"
	)
	func threeFast(led *gpio.LedDriver, delay time.Duration) {
	for i := 0; i < 3; i++ {
	led.On()
	time.Sleep(delay)
	led.Off()
	time.Sleep(delay)
	}
	time.Sleep(2 * delay)
	}
	func blink(led *gpio.LedDriver) {
	gobot.Every(time.Second, func() {
	led.Toggle()
	})
	}
	func main() {
	r := raspi.NewAdaptor()
	led := gpio.NewLedDriver(r, "12")
	work := func() {
	delay, _ := time.ParseDuration("200ms")
	threeFast(led, delay)
	blink(led)
	}
	robot := gobot.NewRobot("blinkBot",
	[]gobot.Connection{r},
	[]gobot.Device{},
	work,
	)
	robot.Start()
	}

view raw blink.go hosted with ❤ by GitHub

Experiment - changing brightness

Let's try something a little bit more complex. I want to be able to control the brightness of the LED. The first thing I did grab the example code (api_led_brightness) from Gobot. My first attempt at running the code failed. The code compiled and seems to run but the LED would not change brightness. It took a bit of head scratching before I remembered the Gobot documentation said something about PWM.

The Gobot documentation references pi-blaster. I found that I needed to setup pi-blaster to get the PWM working.

	#Get Pi-blaster
	git clone https://github.com/sarfata/pi-blaster.git
	#Switch folders
	cd pi-blaster
	#Building
	./autogen.sh
	./configure
	make
	#Manually start pi-blaster
	sudo ./pi-blaster
	#Manually stop pi-blaster
	sudo killall pi-blaster

view raw pi-blaster_setup hosted with ❤ by GitHub

Once I got pi-blaster running on the Raspberry Pi, the example code from Gobot worked. I did encounter a minor weirdness. When I exit the running program, the LED goes to full brightness.

Resources

• Gobot raspi_blink example - https://gobot.io/documentation/examples/raspi_blink/
• Gobot rapi_led_brightness example - https://gobot.io/documentation/examples/raspi_led_brightness/
• Control Brightness of LED Using Raspberry Pi. The code example is in Python. The blog post has a nice description of PWM.
• Gobot documentation for Raspberry Pi - https://gobot.io/documentation/platforms/raspi/
• Pi-blaster - https://github.com/sarfata/pi-blaster
• Software PWM on a Raspberry Pi - http://ozzmaker.com/software-pwm-on-a-raspberry-pi/