Make an LED Blink With Buttons And With Code

This tutorial will show you how to use Viam to make an LED blink with a Raspberry Pi. This is a great place to start if you have never built a robot or a circuit before.

First, you’ll use the control interface on the Viam app to turn the LED on and off. Then, you’ll write code to control the LED using the Viam software development kits.

What you’ll need for this guide

You will use the following hardware for this tutorial:

Project setup

Before you build your circuit, you need to set up the operating system on your Raspberry Pi and install viam-server on the Pi:

  1. Follow the Raspberry Pi Setup Guide to set up the operating system.
  2. Then install viam-server and connect your Pi to the Viam app.

If you encounter issues, reach out to us on the Viam Community Discord.

Build the circuit

The next step is to build a simple LED circuit consisting of an LED and a resistor. The resistor protects the LED by limiting the flow of electricity through the circuit and is called a current-limiting resistor.

You will connect the LED and resistor to the pins on the Raspberry Pi to complete the circuit. Since the only power for this circuit comes from a Pi pin, controlling the state of the pin will toggle the LED on or off.

Understand GPIO pinout

A general-purpose input/output (GPIO) pin is a digital signal pin on a circuit board, like a Raspberry Pi, which may be used as an input or output, or both, and is controllable by software.

Photo showing a Raspberry Pi 4 with a white box around the GPIO pins on the Pi and big letters that say, ‘GPIO Pins.’

Each pin has a specific role, and you can use it only for that role. Some of them are input/output, power (3.3V or 5V), or ground. As you can see in the diagram below, there are 40 pins on the Pi. 26 of them are GPIO pins.

Some of the GPIO pins can be used not only as GPIO pins but for other more specific functions as well. The website pinout.xyz is a helpful resource with the exact layout and role of each pin.

Diagram showing all of the GPIO pins on a Raspberry Pi 4 and their corresponding pin number and function.

One thing that might be confusing is the board pin numbering versus GPIO pin numbering. There are 40 physical pins numbered from 1 to 40. That is board pin numbering, corresponding to the pin’s physical location on the board. Then there’s numbering them by function or GPIO connection. For example, “GPIO 22”. When working with the GPIO pins with Viam, you will use the board pin numbers. For example, board pin 38 is the same pin as GPIO pin 20, but when configuring your machine with Viam, you should refer to it as pin 38.

Wire your circuit

Now it’s time to wire your circuit according to the diagram below. It doesn’t matter what color jumper wires you use but for reference, the blue wire below connects the LED to ground, and the red wire connects the resistor to pin 8 (GPIO 14).

Circuit diagram showing a Raspberry Pi with a red connector running out of GPIO pin 8 to a 100-ohm resistor. The resistor is connected to the long lead of a red LED bulb. Finally, a blue connector connects the short lead of the LED to the ground connection on pin 6 of the Raspberry Pi GPIO pins.

The resistor and LED need to be in series as in the diagram above. To find the right resistor use the resistor color code – for a 100 ohm resistor, it needs to be brown-black-brown. You can use a multimeter to double-check the resistor value or check yours using the photo below.

Photo of a 100-ohm resistor with text overlaid that says, in order, brown-black-brown-gold.

When hooking up the circuit, note the polarity of the LED. You will notice that the LED has long and short leads. The long lead is the positive side, which is known as the anode. The short lead is the negative side, which is known as the cathode. Connect the long anode to the resistor and the short cathode to ground (pin 6) on the Raspberry Pi.

Now that your circuit is wired, reconnect your Pi to power.

Configure your robot

Before proceeding, be sure that you have connected your Pi to the Viam app.

Now it’s time to configure your machine’s components. First, go to the Viam app on your web browser and navigate to your machine’s Config tab.

Click Save Config at the bottom left of the page.

Control your robot using the Viam app

When you configure your board component, the Viam app generates a control panel for it. Click the Control tab to view the control panels for all your machine’s components (in this case, just the board).

Click the board card to expand it. Here, you can click on Get to get the current status of your pin. The first time you click Get Pin State, it should return “Pin: 8 is low.”

Control tab of the Viam app showing the board control panel. The ‘Board Local’ row is expanded, and under the ‘Get’ row, the pin is set to ‘8.’ A red box is around the ‘Get Pin State’ button and the output, which reads, ‘Pin: 8 is low.’

You can now use the Set menu to set the status of your pin to high. Once you click Get Pin State again, it will look like this:

Control tab of the Viam app showing the board control panel. The ‘Board Local’ row is expanded, and under the ‘Set’ row, the pin is set to ‘8.’ A red box is around the ‘Set Pin State’ field.

When you set your pin to high the LED should illuminate. You can set the pin back and forth between high and low, and you will see your LED turn on or off depending on whether you have the value set to low or high.

Congratulations! You have just successfully used Viam to make an LED blink with a Raspberry Pi! You have learned how the GPIO on a Raspberry Pi works, and how to build circuits for LED bulbs.

To make your LED blink periodically, you need to use an SDK.

Control your robot using the Viam SDKs

Now you’re ready to control the LED with code so you don’t have to click buttons to turn it on and off.

In this section, you will learn the basics of programming hardware by using either the Viam Python SDK (software development kit) or the Viam Go SDK to make your LED blink.

Install a Viam SDK

Go ahead and install either the Viam Python SDK or the Viam Go SDK on your local computer. Use which ever programming language you are most comfortable with.

Refer to the appropriate SDK documentation for SDK installation instructions:

Connect your robot to the Viam SDK

The easiest way to get started writing an application with Viam is to navigate to your machine’s page on the Viam app and select the Code sample tab. Select your programming language (Python or Golang), and copy the boilerplate code.

These code snippets import all the necessary libraries and set up a connection with the Viam app in the cloud.

On your local computer, create a file called blink.py or blink.go. Paste the boilerplate code from the Code sample tab of the Viam app into the file in your code editor, and save the file.

You can now run the code. Doing so will ensure that the Viam SDK is properly installed and that the viam-server instance on your machine is live.

Run your code:

In order to interact with the GPIO pins on our Raspberry Pi, you need to import the board component from the Viam SDK.

The Code sample tab automatically adds the board import for you, but it doesn’t hurt to double-check.

Next, you need to initialize the Raspberry Pi board and tell Viam which GPIO pin your LED is on. At the bottom of the main function, paste the following:

Now that the board and LED are initialized, let’s create an infinite loop that will blink the LED on and off. Within the main function, add the following code to create an infinite loop. You can remove the line to close out the connection to your machine, since the infinite loop will never hit that line.

Run your finished code:

If all goes well, you should see your LED blinking on and off again every second!

You can exit this program by pressing Ctrl + C in your terminal window.

If you get an error, you can check your code against the complete code here:

Completed code: https://github.com/viam-labs/LED-Blink

Summary

In this tutorial, you learned to:

  • Set up a circuit
  • Use the Viam app to configure and control a machine
  • Control your machine using the Viam SDK by writing a short program in either Go or Python to make an LED on your Raspberry Pi blink on and off!

Now that you have completed this robotics project, check out some of our other tutorials.