I was invited to contribute something for the Concerned Citizens exhibition happening in Wellington this weekend. The exhibition is hoping to raise awareness about the handling of the 2007 anti-terrorism raids and to get people talking about the relationship between terrorism and the media.
For my submission I designed and built the Sinister Tone Generator – an audio device that you might use to create a soundtrack to make someone appear threatening. The design process is outlined below.
1) Circuit prototyping
I start with a basic circuit in mind and throw it together on a breadboard. Once I’m happy with the basic operation I then go through and substitute component values until the device is ‘tuned’ – the aim is to get the most useful range of settings from each control knob.
Once the circuit is behaving correctly it’s a really good idea to make a formalised schematic diagram. This is handy for personal reference but it also allows me to share my work online and get constructive feedback.
3) Circuit layout
With the schematic drawn up in Eagle it is easy to switch over and draw up a physical layout for the parts. I take this diagram into my workshop and build the finalised circuit on perfboard.
4) Control layout
This unit has 4 control knobs, a toggle switch, audio jack, and LED. I wanted to build this into an acrylic box using a P1 size piece of material (this works out to 90x90x45mm). Squeezing all the controls, circuit, and battery into a box that size is a challenging prospect that is made easier with 3D modelling. I use SketchUp for 3D work, modifying models I’ve found online to simulate the parts I have on hand (a cheap set of digital callipers is a great investment for this task).
I used Inkscape to get my 3D model into a 2D cutting file for the laser and fired up my Personal Factory to cut and engrave the case. I’m thrilled with the result – this is the ideal way to create custom project enclosures.
The finished product will be on display at Concerned Citizens on Saturday and Sunday.
Update: this unit has been sold, stay tuned for more in the future.