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Old 5th May 2015, 05:35 AM   #1
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Default Good audio with LDR's

From now 8 years developing Light Dependant Resistor audio circuits:

Better audio result I perceive is achieved with LDR's when there is no resistance or capacitance in parallel with the LED side cathode. This also includes prior power supply
capacitance and pot resistance if arranged in parallel. The cathode when arranged
to be the only grounding element which is not impossible, creates the best ability
for LDR's to excel as audio optocouplers.

Cheers / Chris
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Old 5th May 2015, 07:16 AM   #2
AndrewT is offline AndrewT  Scotland
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If I remember correctly, the cathode (K) of the LED is the terminal that goes to the more +ve supply.
If you have made this K the "grounded" terminal, then does that mean you have used a negative supply into the LED anode?
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Old 5th May 2015, 07:54 AM   #3
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Hi Andrew
No still V+ ground, the attached schematic shows, how R is solved not grounding,
and in the process solves the LDR turn off issue due to high value of 500k on the pot.

but C is more difficult, solved partially with respect to rectifier switching
separated by an h11f1m ground lifting.

Updated schematic to show diode lift on 7812

Cheers / Chris
Attached Files
File Type: pdf LDR circuit.pdf (12.2 KB, 173 views)

Last edited by Chris Daly; 5th May 2015 at 08:02 AM. Reason: updated schematic
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Old 5th May 2015, 08:34 AM   #4
AndrewT is offline AndrewT  Scotland
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Does your sch show the anodes grounded?
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Old 5th May 2015, 08:38 AM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AndrewT View Post
If I remember correctly, the cathode (K) of the LED is the terminal that goes to the more +ve supply.
If you have made this K the "grounded" terminal, then does that mean you have used a negative supply into the LED anode?
Quote:
Originally Posted by AndrewT View Post
Does your sch show the anodes grounded?
No it's the other way around. I have never got used to this valve/tube jargon.

The cathode of the LED goes to - and the anode goes to +.

Thus all normal LED driven by a +ve supply use a grounded cathode.
i.e. nothing different.
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Old 5th May 2015, 08:54 AM   #6
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Quote:
Originally Posted by AndrewT View Post
Thus all normal LED driven by a +ve supply use a grounded cathode.
i.e. nothing different.
Correct, normal LED driven.
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Old 5th May 2015, 09:17 AM   #7
DF96 is offline DF96  England
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Quote:
Originally Posted by Chris Daly
Better audio result I perceive is achieved with LDR's when there is no resistance or capacitance in parallel with the LED side cathode.
This is hard to believe, given that the only function of the LED is to provide a constant light source from a fixed current input. Have you an explanation for your perception?
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Old 5th May 2015, 10:31 AM   #8
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Referring to Silonex data, now Advanced Photonix, there are no examples where
the cathode is given direct access to ground, to be at the same point as power
supply capacitance, rather it is always either transistor or diode lifted.
The anode with respect to the supply, is given similar even better separation.

See figure 10 and 12, where diode lift occurs and figure 16 where a transistor lifts the cathode

Their purpose would appear to have been to arrive at a best circuit for measurement
purpose, not necessarily listening with a audio system, although they might have
done that too.

Cheers / Chris
Attached Files
File Type: pdf Audio level control with resistive optocouplers.pdf (465.8 KB, 85 views)

Last edited by Chris Daly; 5th May 2015 at 10:51 AM.
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Old 5th May 2015, 04:00 PM   #9
DF96 is offline DF96  England
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OK, no explanation.
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Old 5th May 2015, 05:07 PM   #10
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Quote:
Originally Posted by DF96 View Post
This is hard to believe, given that the only function of the LED is to provide a constant light source from a fixed current input. Have you an explanation for your perception?
But this is not only an LED, it is in tandem with coupling via varying luminessence
to a photocell, that then is matched for best achievable characteristics.
from each.

A Resistive Capacitive circuit has time constants- tau , when wrongly placed the
photocell responds, similarly when better placed the photocell also responds.

Last edited by Chris Daly; 5th May 2015 at 05:33 PM.
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