Category Archives: Android

Controlling a RGB LED attached to a Raspberry Pi through Android

This was a bit of a project that I used to learn some new technology.  Note: I am not an EE and I am just learning how to do this.  Proceed with caution if you want to repeat.

Project Description

I need to be able to control turning on and off an RGB LED utilizing the Raspberry Pi.  I also should be able to turn it on and off using an Android device.


The design is made up to utilize three different components: Raspberry Pi / LED Hardware, Web Service, and Android device.

Raspberry Pi

All the gear that was used was:

  • Raspberry Pi – Model B
  • 5mm High Brightness Full-Color LED
  • Breadboard
  • Resistors
  • 3 x Transistors – 2N3904

Some of the constraints I also have to work with are:

  • Each of the 3.3V GPIO pins can handle a maximum current of 16mA.  They might be able to do more, but from what I read, it would not be for long.
  • The Pi takes about 700mA of the total power without anything plugged in (USB, HDMI, etc), so depending on the power adapter used, there might not be enough power.  In this case, I used a 2A plug.
  • Since each color will require more than 16mA of power to turn on, I need to utilize transistors and the 5V pin from the Pi.  I will use the GPIO to handle closing the circuit on an NPN transistor.  I believe I need to use NPN due to the fact that the LED has a common anode.

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My IOIO for Android is here

The IOIO for Android that I recently purchased has shown up!!!  I haven’t had time to play with it or even know much about how to start playing with it, but I will be figuring it out quickly.  If you’re not sure what it is, a quick description from their website is:

The IOIO (pronounced “yo-yo”) is a board specially designed to work with your Android 1.5 and later device. The board provides robust connectivity to an Android device via a USB or Bluetooth connection and is fully controllable from within an Android application using a simple and intuitive Java API – no embedded programming or external programmer will ever be needed!

So setup as it’s default use, it’s not using the new Google Open Accessory (ADK) protocol, which is what I really want to develop with once I get far enough along in Android programming and being able to do some prototypes on the board.  I figure once I get far enough along, that I’ll be turning on blinking LED’s, and from there the worlds the limit, even though I do know what I want the end result to be with it.

The bad news at this point is that the ADK firmware on it is still very beta.  Even to update the device, I need a PIC programmer capable of programming PIC24FJ128DA206.  So that means until it comes out of beta, I can’t use it for the ADK protocol or I ask some EE friends if they have one laying around.  Even if I take the friend route to update it to the beta, it still has the following problematic caveat:

Due to problems with the accessory library implementation (i.e. the Android OS code supporting the protocol) – the IOIO connection will not be properly closed when pausing (and exiting) your IOIO app. When the app is resumed (restarted) it will hang. The current workaround is to physically disconnect and reconnect the IOIO (or power-cycle it).

This is because of a problem in the Android OpenAccessory library preventing the app from gracefully closing the ADK connection. To work around this problem, detach and re-attach the IOIO when that happens (or power-cycle it). Another option is to force-close the app.

Not something that I would call usable in a real life situation.  Hopefully it does get resolved though.  At this point though, since my original plan is for a single use at this point, if all else fails, I’ll just use their implementation of the communication protocol for the initial project.  Either library I use in the end, both will be good learning experiences on making and developing for new accessories to work with Android.