Ahh... That would be the coils for this idea.

---
James.
 
 

> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of Peter L. Peres
> Sent: 2005 Feb 18, Fri 11:25
> To: Microcontroller discussion list - Public.
> Subject: RE: [EE] Low cost encoder. Is it a compass?
> Importance: Low
> 
> 
> 
> On Thu, 17 Feb 2005, James Newtons Massmind wrote:
> 
> > No, I was thinking of an oscillator. I know from my dads old tube 
> > radios that LC or "tank" circuits will tune an astable 
> multiviberator 
> > (oscillator) to a frequency that can be changed by passing a metal 
> > core though the coil of the inductor. Most old radios used variable 
> > capacitors, but at least one that I remember seeing was tuned by 
> > rotating another coil inside the main coil.
> >
> > Simple metal detectors are two oscillators setup so that one is 
> > affected by the presence of metal and the other is not. The 
> difference 
> > between the two is an audio "beat" frequency which is 
> amplified and fed to the speaker.
> > http://home.clara.net/saxons/bfo.htm
> >
> > Obviously, the change in frequency isn't much, but perhaps it is 
> > enough that a fast processor can detect it. If not, a beat 
> frequency 
> > oscillator isn't much to add.. All the components are low cost.
> 
> If you are trying to make something accurate then surplus selsines
> (transmitters) could get you a fair distance in the right 
> direction for relatively little money (I saw some for $5). A 
> selsine is a rotary LVDT with 3 phases. You can use only two 
> phases if needed. These have the potential to resolve better 
> than 0.1 degrees if in good condition.
> 
> Peter
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