[LAU] A crazy idea

Jonathan Gazeley jonathan.gazeley at bristol.ac.uk
Thu Mar 4 04:48:00 EST 2010

Morning LAU,

As I cycled to work this morning, I had a crazy idea. It's just 
daydreaming and will probably never happen, but I wondered if anyone on 
the last has any useful/interesting thoughts.

I want to measure how fast I'm turning the pedals on my bike (the 
"cadence") and synthesize/sample the sound of an internal combustion engine.

As far as I can work out, there are three major parts to this.

1. A sensor that can measure my cadence. A simple magnet switch that 
triggers once a revolution won't be enough to measure the cadence with 
sufficient resolution, since my cadence is usually between 50 and 80 
rpm. I would probably need to mount multiple magnets spaced equally 
around the chainwheel and have a single sensor on the frame. Then I have 
to get it to supply this information to my control program.

2. I need a control program that can read in the input from my cadence 
sensor and convert a cadence reading of "66 rpm" into a frequency that 
should be sampled/synthesised, e.g. "500 Hz" (I'm making these numbers 
up). It will also need to be able to somehow smooth out the readings, 
perhaps by interpolation, so when I accelerate, the sound of the revs 
climbing doesn't increase in obvious steps. It could also have other 
logic, e.g. when my cadence is 0 rpm, the sound of the engine is idling 
rather than off.

3. I need a synthesiser or sampler that can take an input from my 
control program and make the sound of an engine (or more likely, a sine 
wave to start with). I've never sampled or synthesised on a computer 
before but this engine-specific sampling technology already exists in 
video games, such as torcs[1].

I have absolutely no idea why I would want such a device - just for the 
fun of building it, I guess. I would like it to work in realtime (rather 
than later generating the soundtrack from recorded cadence data). The 
thought of sitting at the traffic lights with my earphones in and then 
hearing the mighty roar of a V8 as I pull away would be really satisfying...

[1] http://torcs.sourceforge.net/

Any thoughts - useful, interesting, humorous, or otherwise - are welcome!


Jonathan Gazeley
Systems Support Specialist
ResNet | Wireless&  VPN Team
Information Services
University of Bristol

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