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Old 16th March 2004, 12:35 PM   #1
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Default LED to LDR amplifier

light emitting amplifier.
i was talking 2 a friend about electronics, and i told him of a thing called Light Dependent Risistor, a.k.a LDR.
and the it struck me.
i think i have my work cut out for me, but check the idea on wicth i think my light emitting amplifier is based on.
tell me what u think.
is it already invented?
is it operational with low distortion(with a buffer)?
if it had been invented, what is it called?

am i on to somthing?
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Old 16th March 2004, 01:10 PM   #2
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What is the idea? Is there supposed to be a link or schematic? What are you thinking about?

Jan Didden
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Old 16th March 2004, 01:24 PM   #3
sreten is offline sreten  United Kingdom
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The basic device is called an opto-isolator.

I believe they can amplify with the version where the
LED provides the base current of of an isolated transistor.

Without the isolation requirement they have little use
in normal circuits, standard circuitry performs better.

sorry again....... sreten.
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Old 16th March 2004, 02:35 PM   #4
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Quote:
Originally posted by janneman
What is the idea? Is there supposed to be a link or schematic? What are you thinking about?

Jan Didden
ya
i added a pic.
not working.
hmm.
Quote:
Originally posted by sreten
The basic device is called an opto-isolator.

sorry again....... sreten.
ur always sorry.
oh well, at least u dont lie!
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Old 16th March 2004, 03:18 PM   #5
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Default Re: LED to LDR amplifier

Quote:
Originally posted by electro samurai
light emitting amplifier.
i was talking 2 a friend about electronics, and i told him of a thing called Light Dependent Risistor, a.k.a LDR.
and the it struck me.
i think i have my work cut out for me, but check the idea on wicth i think my light emitting amplifier is based on.
tell me what u think.
is it already invented?
is it operational with low distortion(with a buffer)?
if it had been invented, what is it called?

am i on to somthing?
It's invented since decades but nowadays you have "analogue opto coupler" which can be used for this purpose. You have also led or ligth bulb + LDR in one case.

This analogue optocoupler consists of one LED and two photo transistors. One of the is used for feedback for the LED. None of these opto solutions produces any high fidelity but they work alright for industrial purposes.
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Old 16th March 2004, 06:15 PM   #6
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Used for optical compressors. The input drives the led, and the ldr is used to reduce the gain of the output.
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Old 16th March 2004, 06:50 PM   #7
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Seems what Your talking about, electro samurai, is a vactrol, a led and a ldr in the same casing. Found in several guitaramps. A realy lousy component. Also notice that all ldr´s have "memory" that is they adjust to variations in light slowly, faster action on increasing than decreasing lightintensity. This is a fun to play with component for efectboxes for instruments and such but useless in reproductve amplificarion
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Old 21st March 2004, 04:02 PM   #8
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its seems as there are many names 4 this silly divice.
indeed silly.
the compressor idea sound cool.
ill check it out.
thx 2 all that responded.
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Old 21st March 2004, 05:07 PM   #9
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Default Re: Re: LED to LDR amplifier

Quote:
Originally posted by peranders

It's invented since decades but nowadays you have "analogue opto coupler" which can be used for this purpose. You have also led or ligth bulb + LDR in one case.

This analogue optocoupler consists of one LED and two photo transistors. One of the is used for feedback for the LED. None of these opto solutions produces any high fidelity but they work alright for industrial purposes.
I have used HCNR200 HCNR201 and IL388 analog opto-couplers to isolate high voltages from ADC's -- they are most often used in a servo configuration on the send side to reduce distortion. I haven't run an audio signal through to see if there is any appreciable distortion, my application was in measurement and isolation. The linearity in my application was better than Agilent stated on their website (i.e., I can confirm better than 0.01%). Analog opto-isolators are also used in medical applications -- like EKG --

Since the opamp in the servo is a photodiode (large capacitiative surface area) the amplifier it is pretty easy to get it to oscillate, care must be taken in compensation --

by the way -- the next big thing will be in using the wasted base current to generate light -- I believe that IBM had a press release to this effect 3 or 4 weeks ago.
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