Pickup lines
I have a whole cupboard full of interfaces and sensors but realise that not everyone is so lucky, for that reason I am often on the look out for cheap alternatives. A couple of weeks ago I had the idea of using a guitar pick up connected to the microphone input of the computer. So I bought one from ebay for a pound. It had to be delivered from China but I got it just after Christmas and popped down to the lab to try it out. The idea was to use audacity to analyse the signal given when the pick up was placed under a vibrating wire. It worked really well when I used the sonometer but not so good when the wire was simply stretched between two lab stands. The pickup consists of coil wound around a magnet, the moving steel wire causes a change in the magnetic field which induces an EMF in the coil (Faraday's law) so will detect the movement of any object provided it is made of a magnetic material. I experimented with a steel pendulum bob and got fairly good results. Each time the bob passed over the pickup an EMF was induced. By analysing the signal using audacity it is possible to calculate the time period of the pendulum. In this way the pick up could be used as a timing device. I have seen other uses of Audacity where coils are connected to the mike input. A signal is induced by moving magnets in and out of the coil. I am a bit wary of trying this as I'm not sure what PD I can apply to the mike input without damaging my computer.