I’m building a Blendophone for Maker Faire. What’s a Blendophone? It’s a “musical” instrument made from eight blenders controlled by an iPhone and an Arduino. My friend Usman Muzaffar is writing an iPhone app to control the beat sequencing and solo input, while I’m building the hardware and an Arduino sketch to switch the blenders on and off.

The first challenge I had was controlling blenders from an Arduino. I decided to go with the PowerSwitch Tail, which is a neatly packaged isolated AC relay circuit that can be controlled from a 5V DC signal — very safe, very easy. The PowerSwitch Tail draws about 40mA of current to do its thing, which is the limit of what an Arduino digital pin can reliably push. In practice, I found the Arduino could usually control the PowerSwitch Tail on its own, but would occasionally fail to trip to relay. To be safe, I decided to create a driver circuit for each of the eight blender outputs. I created a drawing of the circuit in Fritzing, and then prototyped it on a breadboard.

Once this was working, I made things a bit more permanent. I used a ProtoScrewShield to solder the eight transistor circuits, and provide eight screw terminal pairs for the output to the PowerSwitch Tails. This works great, and gives me a nice solid connection to the blender controls. You could also use a standard MakerShield and a ScrewShield to do the same thing.

In the next installment I’ll talk about making this system wireless, using XBee radios.

In the Maker Shed:

PowerSwitch Tail