Prototype #1 for Magnetic Sense Trainer
Building the trainer is fairly easy to build (see schematic above) for anyone who would like to replicate one for themselves. However, I would highly suggest buying your parts online because purchasing them from radio shack will run you nearly $70 and you will have to get lucky and hope that they actually carry IC's at all. But I have a pretty good one near my house that has a pretty larger stock of components and they had everything I needed.
For anyone looking to build one for themselves the voice coil is just a bunch of enamel wire that was wrapped around a 9v battery and bound with electrical tape. This could work better with professional voice coils. You can buy voice coils online or pull them out old speakers if you do now want to make one yourself.
Here are a couple more pictures: