DIY linear servo driver?

[David_Web]

I want to start simple before I build my own linear drive.

I have a speaker that I want to use in a servo manner by reading it's position and then control it with an analogue signal. (-2 to +2V or similar) 0 will be midpoint.

A simple audio amplifier could be used to drive the coil itself to eliminate noise that I imagine would come from a shopper. Or just making the project simpler.

Could a Hall effect sensor and a small magnet work as a position reader?
Or several to get scalable movement when building larger rigs.

Oh, and I don't know a lot about electronics. It should be enough to put it together though.

If it works great it might even work as a subwoofer.

[vger]

I think you will experience problems with the linear Hall effect device. Your magnet structure even possibly the feild of the voice coil itself may alter what you are sensing. In the old days of big computer hard drives, voice coil head possitioners were used. Some of them were really massive with magnet structures weighing upwards of 100 lbs and voice coil lengths of 6 inches. The position of them was generally sensed using an LVDT. It was commonly attached to the voice coil through a hole in the center of the magnet center pole. Since they operate at up to 50 Khz drive and sense frequency they were unaffected by the voice coil drive.
http://www.macrosensors.com/lvdt_mac...ial/index.html
I had a small LVDT and it's indicator once, made by Swiss Precision and it's readout was in mils (thousandths of an inch) with 2 places to the right of the decimal! 0.00001 inches !

Enjoy
Steve

[David_Web]

That it awesome! I have to build one just to play with.

A simple comparator between input voltage and sensor voltage will just make it oscillate so it won't be that easy.

I have read around a little and a simple PID controller could be made with two resistors and two capacitors. Will that be enough?
I don't know how to program a PIC so that won't be an option yet.