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A photo-transistor is much faster than an LDR.
A photo-diode is faster than a photo-transistor.
Can I generate changes in resistance with any of those devices?
Going back to the LDR+LED, can I make the resistance changes go faster?
Oh no they're not, the change in resistance is perceivable - it takes a second or two for a CdS cell to go from its dar resistacne to light resistance.
Hi prprog,
Perhaps if you tell us what the device is being used for someone can offer some more insight into what might a good solution.
As Nigel asked, how fast do you want it to be? You said you want it to be "faster" but how fast is fast enough, and what are your criteria?
Torben
Thanks to all.
How fast? Well I cannot give a fixed or determine time. This is for an electronic musical instrument, so it more about that for "slow musical passage" it works fine but for fast musical sections it is left behind.
Sorry I cannot be more specific. I will read more about Nigel (and other suggestions) on Phototransistors and photodiode.
Thanks again.
OK. One thing you might want to look into is using a JFET as a voltage-controlled resistor: **broken link removed** (there are lots of other pages on the net on that topic).
Do you need the resistance of the device to be fairly linear?
Torben
Thanks for the web site reading...but to dense for me. Still on the basics. Sorry.
No it does not have to be linear...Few month ago I try and failed to used a MPF102 (this is the FET I have ) it need a negative voltage to operate which I did not undertood how to generate - (I am still undertanding the term "less positive"). Can you suggest a circuit that I can re-try with the MPF102?
Thanks,
Comparators are much faster than DVMs.How do you know this? It takes about that time for a multimeter to register the change alright but it certainly does not take that long.
I made one of those and the light came on instantly. Their response time is a matter of milliseconds.
that doesn't change the fact that their repsonse time is milliseconds.
You're talking a couple hundred milliseconds at the very most.
Exactly - incredibly slow - electronics works in picoseconds or nanoseconds, 100's of milliseconds is so slow it's not moving at all!