Effect of LDR

[digitalsea]

Hi all,

I’ve been looking at projects using LDRs and want to understand their function and effect on the actual sound.

Why use these instead of standard resistors? Do they have a variable effect? How does this work if the light from the led is constant?

Sorry, bit of a ramble, I love the builds that involve LDRs, but want to know how they influence the design.

Thanks

 

[BurntFingers]

Well, a standard resistor would always be in the circuit. An ldr is 2 parts- the light (led) and the ldr which picks up the light from that led.

The light is triggered by a signal, say a guitar input, which causes it to light up which tells the ldr to do something because it picks up the light put out by the led.

If you have a look around they're used on the warden compressor to tell the ldr to activate the circuit, so it's like a trigger. You'll see them on tremolo circuits where the light pulses in time with the speed knob.

So that's the general idea. A resistor is always "on" (unless it's switched out) whereas an ldr will only turn on when the led is triggered by something.

 

[TGP39]

Hi digitalsea,
It is correct that the LDR is a device that will give you variable resistance. It’s important to understand how a LDR works. https://www.watelectronics.com/light-dependent-resistor-ldr-with-applications/

Take a look at this site for an informative look at LDR mechanism and functionality. As to how the variable resistance will effect sound is completely dependent on the circuit design.

Hope this helps and keep learning.
TGP39

 

[Gt6371]

Well, a standard resistor would always be in the circuit. An ldr is 2 parts- the light (led) and the ldr which picks up the light from that led.

The light is triggered by a signal, say a guitar input, which causes it to light up which tells the ldr to do something because it picks up the light put out by the led.

If you have a look around they're used on the warden compressor to tell the ldr to activate the circuit, so it's like a trigger. You'll see them on tremolo circuits where the light pulses in time with the speed knob.

So that's the general idea. A resistor is always "on" (unless it's switched out) whereas an ldr will only turn on when the led is triggered by something.

For some reason my Leds aren’t lit up.

 

[EGRENIER]

Interesting, if I remember well the Delegate compressor was using an LDR rated for 500K dark.. Which I understood was providing resistance when the LED is off (not lit) and the resistance would drop to zero once the LED go on (gets lit). Is that correct ?

Also, is there the opposite ? LDR that provides resistance when it detects light ?

 

[nate433]

Interesting, if I remember well the Delegate compressor was using an LDR rated for 500K dark.. Which I understood was providing resistance when the LED is off (not lit) and the resistance would drop to zero once the LED go on (gets lit). Is that correct ?

Also, is there the opposite ? LDR that provides resistance when it detects light ?

Bump for wondering if this exists

 

[EGRENIER]

Bump for wondering if this exists

From all my research, no….

 

[chris.knudson]

As a noob to optocouplers, I think this is an interesting discussion. One question I have about LED/LDR combinations is how to determine the best LED color in different scenarios. Is there a way to determine that from the data sheet of the LDR?

 

[Diynot]

As a noob to optocouplers, I think this is an interesting discussion. One question I have about LED/LDR combinations is how to determine the best LED color in different scenarios. Is there a way to determine that from the data sheet of the LDR?

The data sheet will sometimes give the wavelength (in nm) that the LDRs respond best to. You can take that and look at a visible spectrum graph and match it up

 

[benny_profane]

The data sheet will sometimes give the wavelength (in nm) that the LDRs respond best to. You can take that and look at a visible spectrum graph and match it up

Or ref the LED datasheet. It should give a wavelength.