Initially I tried using some freestanding bells that were struck by solenoids attached to a Raspberry Pi. However I found that the solenoids were too noisy and there were power and wiring issues with the Pi.
I concentrated on the idea of using a motor with some form of striker attached. I took some motors from Sony PlayStation controllers as these had low voltage and amperage requirements. I attached electrical wire connectors to the spindles and inserted copper wire from electrical cable into the top. I bent the wire at approximately 45 degrees.
I dismantled a wind chime and built a wooden frame to suspend the bars from.
The whole arrangement is a bit Heath Robinson and deliberately so. Michael Nyman in his book Experimental Music; Cage and Beyond writes of John White's machine music '... being English they are ambling, friendly, self-effacing systems, which may break down ...'
I recorded the sound of each bar being struck by a screwdriver, edited those clips and transferred them to the Raspberry Pi. There were two programmes that ran simultaneously on the pi. The first operated the motors, it decided how many motors would run, which motors they would be, how long they would run for and how long the gap was between spins. The second programme played the audio clips back at random intervals at varying loudness through the speaker system. Here is a photo of the machine connected to an ibook running debian:
The original wind chime that I used had five bars but because of the length of them (the longest was 30 cm long) I found that the frame required was really too large. I got another, smaller wind chime (longest tube 16 cm) so that I could attach all five bars to a frame. I also added an ultrasonic sensor to the system that meant that as people approached the machine more motors span and as they got further away fewer span.
Last weekend I decided to make the machine more controllable and connected it to a midi controller via the Raspberry Pi. I have subsequently played it using both a midi keyboard and casio digital horn as you can view in the video below.