Drawdio

A finished Drawdio without a printed mount

Since even before I started the designs for the modular robots, I was greatly interested by the original Drawdio circuit concept, that you could use a simple circuit to interact with the surrounding world and for the world to, in turn manipulate the outputs of the circuit.

In this instance, it  the Drawdio is a basic electronic circuit which utilises the use of a 555 timer chip to produce an astable output frequency. The speaker frequency depends upon the resistance of the input circuit, which comprises of the graphite pencil and your body. As the line that you draw gets longer, the input resistance increases, therefore different tones can be heard.

The Drawdio was my very first circuit that I designed in Eagle, previously, I had used the very basic but easy to learn package called Fritzing, however, this provided very few components and little flexibility when it came to board layout. After attending a couple Cambridge PCB Makers sessions (Forum found here, Saar's blog here) I had a much greater (not yet great, just greater) understanding of PCB design software and decided to give Eagle a go. I then designed a derivative of the Drawdio circuit, but it functions the same.

The Schematic

There is no difference between PCB versions 0.1 and 0.2, except the fact that v0.2 had a general track layout clear-up as I got rid of the vias and added two ground planes.

The PCB

I also designed and developed a custom 3D printed mount for the Drawdio circuit board, it was designed in Solidworks and printed with transparent resin on a FORM 1. As you can tell from the following pictures, it took many revisions to achieve the correct tolerances on items such as the PCB and speaker, as they are designed to "clip in". I have not yet completely finished the mount however, as I intend to design a clip mechanism to allow for the CR2032 battery to be easily replaced when it runs out - it currently lasts ~500 hours with a TLC551 timer, (which works down to 1v for a coin battery to be used) so this action would be infrequent.

Top, left to right: PCB mounts v0.1, v0.2, v0.3, v0.4 and v0.5
Bottom, left to right: Speaker mounts v0.1 and v0.2

The bottom mount is the first "final" print, while the top is a more compact version

NOTE: I do not claim any credit for the original Drawdio circuit and the MIT project website can be found here. I did, however design the mount.

The latest Drawdio PCB design files (v0.2) can be downloaded from Dropbox.
The Drawdio 3D design files (v0.5) can be downloaded from Dropbox - (STL and Solidworks file types)