Jonathan's blog

As I cycled to work this morning, I had a crazy idea. It’s just daydreaming and will probably never happen, but it’s fun to think about. I’ve already posted this idea to the linux-audio-user mailing list in case anyone there has any insights on synthesising/sampling engine sounds.

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, and I will need to sample more than once a second. 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.

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…

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

Strada Cadence

Over the years I’ve had a number of cycle computers. Most have been Cat Eye, although some haven’t. It’s clear to me that Cat Eye make the best cycle computers – both in ease of use and in build quality (which is rather important when it will be subjected to rain, sun, vibration, heat and cold).

A few months ago I fitted a Cat Eye Strada Wireless to my racing bike. It was my first wireless computer and I’ve been extremely impressed with the results. The computer itself has a single-button interface and is nice and easy to use. The numbers are big enough to read easily while you’re riding.

But recently I’ve been tempted by the gimmick^[1] of seeing my pedalling cadence too. I enjoy cycling and I love gadgets. So I ordered a Cat Eye Strada Cadence for my racing bike, and moved the Strada Wireless to my commuting bike.

The Strada Cadence is a wired computer, and you need to go through the rigmarole of attaching cables to your bike frame with cable ties. Unusually, the sensor attaches to the inside of the chainstay of the rear wheel. The other sensor attaches to the outside of the chainstay so it can sense the pedals going round.

Installation is no more tedious than any other wired computer, and you get loads of tiny black cable ties in the bag. The only tricky bit is strapping up the loose cable by the sensors. They both share a common wire back to the computer, which splits off into a Y around 8 inches from the sensors. If the shape of your bike means the sensors have to be at different positions then you’ll have to take up the slack cable securely. Unless you want it to go in your rear wheel!

I don’t know if my racer is unusual, but with the pedal crank magnet in place, it was a lot more than 3mm from the chainstay sensor, which is the distance it has to be to make it work. I got round this by putting a piece of rubber in between the crank and magnet to move them a bit closer. An easy fix, especially if you have spare rubber feet lying around – but it’s a shame Cat Eye didn’t provide them.

The FlexTight bracket is great, as it easily lets you install the computer on the handlebars or the stem. On both bikes I have the computers mounted on the stem, to save maximum room for lots of lights.

Using the computer is also easy – just press anywhere on the unit to “click” it and cycle through the modes. The Strada Wireless and Strada Cadence both have the same modes, except that the Strada Cadence also has a cadence mode. This simply shows your current pedalling cadence, in revolutions per minute. There are no functions to show you the average or maximum cadence, like there are with the speed.

So, in summary, I would absolutely recommend that you get a computer from the Strada range. Up to you if you want to go for the wireless or cadence options. They might be a few quid more than the competitors, but it’s well worth it for the quality.

[1] Whether you see this as a gimmick or a training tool is entirely your own opinion!