On Mon, 5 Jun 2006, Padu wrote:
> So my question follows: how do I translate that type of signal to useful 
> digital values? (i.e. How many degrees turned on each axis)?

First you translate into degrees/second, and then integrate that to get 
degrees turned. The waveforms move up and down because the sensors use 
some form of lvdt to make the signal and the change in amplitude and 
bias is a side effect of that. You need to ignore the amplitude shift 
and detect peaks or zero crossings (precisely, better than 0.2% of the 
period resolution), on all axes simultaneously. Then you will have the 
instaneous difference in phase between axes, for each two axes, which 
can be scaled to degrees/second, as a signed number. By summing these 
degrees per second into an accumulator you have a crude integrator, and 
the accumulator should indicate degrees. It will drift like crazy. I 
would start by making only one axis, analog, and get some numbers for 
the accuracy and drift of that thing. You can 'measure' its accuracy and 
scale factor (approximately) by putting it on a turntable (use batteries 
for power and try to get the axis pointed right so only one axis gets 
input from the spin).

An analog phase meter can be built easily, you can find schematics on 
the web. It might use a RS flipfop and a few gates, or an analog 
multiplier.

Peter
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