[sdiy] opto LFO

[Theo]

Typical range of a LDR is a few meg when dark to a few k (or less) when in
full light.
Actual values vary quite a bit depending on the device.

Don't use a voltage divider setup like the rate pot in the ASM LFO,
but just the LDR as current limiting resistor from comparator output to the
timing cap.
Should work for a reasonable wide range,
you may have to experiment with the value of the timing cap though.

When you measure the LDR in maximum light and dark conditions,
you can predict the LFO rates like this:

LFO frequency = (1/(4RC))(R2/R1)
where:
C= the value of the timing cap.
R= LDR resistance.
R1= the resistor from triangle out to comparator + input.
R2= the resistor from comparator out to comparator + input.

Theo



From: <cris at music-service.nl>


> Hi,
> i want to build a OPTO LFO, that means to change the frequency of
> the LFO with a optical resistor.
> The problem is thet this resistors are 100 ohm, this is too small to
> control a octave if i use the ASM-1 LFO...
> I want to have control over the full range of the audiospectrum, i don't
> need a acurate range but the full scale is inportant.
> Can somebody to help me ????
> Thanks in advance,
> Cris