a light dependant resistor is made up of an LED and a Photo Sensitive Resistor.
is the resistor at least resistance when the LED intensity is at Full and full resistance when the LED is off?
lets say the resistor is a 20k and the LED is off would this mean that the resistor is 20k (full resistance)?
now the same 20k resistor at full LED intensity (brightness) would be 0k (least resistance)?
or have i got it backwards.
is the resistor at least resistance when the LED intensity is at Full and full resistance when the LED is off?
lets say the resistor is a 20k and the LED is off would this mean that the resistor is 20k (full resistance)?
now the same 20k resistor at full LED intensity (brightness) would be 0k (least resistance)?
or have i got it backwards.
It goes that way around. The more light, the lower the resistance.
Although LDRs lowest resistance is most likely a few kOhms. No light / maximum resistance is from several 10kO to several MOhms. It depends on the spec. Datasheets will hold values.
They are slow devices though so offer damping. If you kill all light, most datasheets will spec resistance after 10 seconds of total darkness...
Although LDRs lowest resistance is most likely a few kOhms. No light / maximum resistance is from several 10kO to several MOhms. It depends on the spec. Datasheets will hold values.
They are slow devices though so offer damping. If you kill all light, most datasheets will spec resistance after 10 seconds of total darkness...
Shine a light source on an LDR and the resistance reduces. They are not LED. If you has a germanium OC71 and removed the cover, you will have a fully functioning LDR.
ok a resistive optocoupler then.
hhmmm i now see the problem of the LED failing to try and gain 0 resistance.
thanks, i think i understand a little more now 🙂
hhmmm i now see the problem of the LED failing to try and gain 0 resistance.
thanks, i think i understand a little more now 🙂
the Lightspeed type of LED/LDR have a range of ~20r to ~1M0, from max LED current to zero LED current for the LDR element.
I believe they are a composite of LED to generate the light and CDS as the variable resistor.
For maximum range of attenuation the problem is minimum resistance of LDR in the shunt part of the resistive divider.
With only 20r as the reliable minimum resistance and with 10k as the maximum repeatable and channel to channel balanced, then the maximum attenuation is 20/(10k+20) = -54dB.
For some operators this is too small a range.
You can add -6dB to get -60dB by paralleling two LED/LDR for the shunt element.
You do have the option to add a mechanical "mute" switch, if minus infinity is required.
I believe they are a composite of LED to generate the light and CDS as the variable resistor.
For maximum range of attenuation the problem is minimum resistance of LDR in the shunt part of the resistive divider.
With only 20r as the reliable minimum resistance and with 10k as the maximum repeatable and channel to channel balanced, then the maximum attenuation is 20/(10k+20) = -54dB.
For some operators this is too small a range.
You can add -6dB to get -60dB by paralleling two LED/LDR for the shunt element.
You do have the option to add a mechanical "mute" switch, if minus infinity is required.
Last edited:
No. An LDR is a photo sensitive resistor. I believe you can buy a package which includes both an LDR and an LED - maybe some people wrongly call this combination an 'LDR'?Bibio said:
No. An LDR is a light dependent resistor, approximately linear. A bare OC71 is a light dependent transistor or diode, rather nonlinear like any diode.JonSnell Electronic said:
- Status
- Not open for further replies.