LDR and LED

[sbirkenstock]

Hi Everybody,

I tried to make a smoother Tremolo with an LDR and an LED.
My oscilloscope told me differently....
The resitance is going up very smooth (nice round arch going up),
but it goes down very rapidly.
On the oscilloscope it looks kind of a shark fin.

Is this an issue of the LDR or the LED?
Are there any other light sources that work in an 9v world that would be smoother?
Or should I try different LDR´s?

My LDR is from Germanys electronic store CONRAD, and the data sheet say´s between 0 and 180k.
Are there other ones around? With less resitance?

Best regards,

Stephan 

[Kipper4]

It's probably more to do with the type of lfo you are using.

Post a schematic so we can see what you are doing please so we can help.

[Mark Hammer]

1) LEDs are instantaneous any lag in turning on or turning off is a function of what they are fed.

2) LDRs have specs for rise and fall time.  On the other hand, when we buy 25-cent photocells, we tend to get no more information about them than their bright/dark resistance range and maybe the wavelength their peak sensitivity is at (expressed in nanometers; e.g., 630nm).  When Craig Anderton used to recommend the CLM6000 optoisolator for his projects, it was selected because of its rise and fall time characteristics, as well as the resistance range.

3) Having said that, one can often either select an LFO with particular waveform characteristics, or shape the rise-fall characteristics of the LFO to complement how you want the LDR to behave.  So, for instance, if the LDR rose slowly when lit and fell quickly in darkness,  the LFO would probably be adjusted/selected to provide a contrary action (fast rise, slow fall) that might result in the more desirable feel to the sweep.

[ElectricDruid]

I second what Mark said - rise and fall times for LDRs can be wildly different. x10 different, sometimes. The LED will be instant on and off, so there's no problem there.

Obviously if you want to slow a fast response down, you can alter the LFO wave shape to give you a (for example) slower rise time, but you can't compensate for a too-slow LDR by making the LFO faster!

HTH,
Tom

[armdnrdy]

You can also "smooth" out a tremolo by reducing the depth/amplitude of the LFO.