CD Robot

This is an automatic CD changer that I built to rip my CD collection. It is uses a pair of motors from a discarded HP printer for horizontal and vertical drive (and also the horizontal drive train itself), and a vacumm pump to grab the CD. The PC interface uses a Phidgets 8-8-8 IO board, and the control script is written in Python.

There are 6 sensor switches:

The CD grabber took some trial and error. The first attempts used a mechanical pickup, but were not reliable. A bit of research revealed that this is not how the pros do it. I found this 12V DC vacuum pump online, and with some tubing and a little suction pad, it picked up CDs well. In fact, it was too good - now the CD would not release when the pump (which does not, unfortunately, blow when current is reversed) was turned off. The answer was to make the air line slightly leaky - a tiny pin hole in the tubing, and a long wait after the pump is switched off. You can see the sucker (made from one of those things for sticking hooks on a wall) lift about 8 or 10 seconds after the pump cuts out.

The DC motors are not driven at the rated 12V. The interface electronics has some adjustments to reduce the speed by using a lower voltage. This thing does not need to run as fast as a printer head! When the head is lowered, a small braking voltage (about 1 or 2V) is applied to the motor so that the head does not drop too fast.

This thing was fun to build (OK, it took a lot of work, but I enjoyed the challenge) and it is quite reliable. The flakiest part is the script that drives Exact Audio Copy. EAC is not easy to control automatically, it really is meant for manual operation only. But it is the best CD ripping program out there, so I stuck with it.

So, now my CD collection is finally getting digitised properly. There is still a lot of manual work - cleaning up tags and getting rid of duplicates and rubbish in my large library. But it is very cool to be able to listen to anything, anywhere in my home (I use a Logitch Squeezebox system, which I am impressed with). Now - anyone want to buy some CDs?