[sdiy] LDR optocoupler blowout

[John Speth]

> >> With the slow response of LDRs and the regular means of controlling
LED
> brightness being PWM, I wonder if these could be used as a digitally
> controlled resistor, assuming that one clocked the PWM comfortably above
the
> response time of the LDR. Just a thought.
>
> Some senior design students I was informally advising did exactly that,
using
> PWM to control the Vactrols in a Buchla-style lowpass gate circuit. It
worked
> pretty well IIRC.

These two comments got me to thinking: I wonder if one could use a speedup
circuit to compensate for slow LDR response by driving it harder for quick
changes and less for slow changes.

At my professional job we had to speed up output response of thermocouples
measuring the heating of a thermal mass from the instantaneous turn on of
a laser.  Since the heating equation was linear we applied a simple high
pass RC circuit at the output to compensate for the slow response from the
thermocouples.  R and C where chosen to match the required response from
the mass thermal time constant.  Later on we used a digital filter to
compensate but the theory was the same.  We also applied the theory to
speeding up analog panel meters with slow time response.

Is that feasible or am I ignoring some fundamental fact that makes this
impossible?

JJS