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Old 28th June 2013, 02:51 AM   #5071
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Quote:
Originally Posted by scm View Post
George..putting the fitment issue aside, are there any advantages to be had by going with an upper end pot like an Alps ?
No
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Old 19th July 2013, 10:44 PM   #5072
gadut is online now gadut  Indonesia
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Any additional failsafe circuit in case the ldr is dead? If the ldr dies,is it full volume or 0? I'm expecting to get it as 0 to avoid 'BOOM' on amplifier and speaker

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Old 19th July 2013, 11:32 PM   #5073
wlowes is offline wlowes  Canada
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Originally Posted by gadut View Post
Any additional failsafe circuit in case the ldr is dead? If the ldr dies,is it full volume or 0? I'm expecting to get it as 0 to avoid 'BOOM' on amplifier and speaker

Regards
the resistance goes to max, around 1m ohm. So it depends on which one dies
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Old 20th July 2013, 01:22 AM   #5074
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Originally Posted by gadut View Post
If the ldr dies,is it full volume or 0? I'm expecting to get it as 0 to avoid 'BOOM' on amplifier and speaker

Regards
If you make it as I have posted, if power is pulled the volume goes up just a touch then fades away.
If the shunt only ldr goes open circuit, (I have never seen this) yes you will get max volume, this will only do that if you over power them, mine run below max rating.

Cheers George
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Old 25th July 2013, 08:45 PM   #5075
cedricb is offline cedricb  Europe
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I'm trying to experiment with the Silonex's reference circuit from figure 10: Advanced Photonix Canada, Inc.: Technical Reference: Audio Level Control with Resistive Optocouplers.

I'm using an Arduino board with:
- PWM 8bits signal (5V) for the control
- 2.048V as an input
- the output is plug to an input of the Arduino so I can measure the ADC value in my program

Do I need to put a kind of load on the LDR side of the Silonex device to simulate an amplifier? ...somethime I can get low as 48mV on the output and most of the time around 110-130mV

Another thing is ~3.6V the optimum voltage for the OP1 (from the series/shunt), instead of directly using 5V ?

Otherwise I'm getting a slightly S shape for the output response curve, so mainly linear in the most part of the curve. This is with a matched pair of LDRs. At the moment I'm just playing with a single channel.

Just a side note I'm getting my first output from the 60th value of the PWM control input; is it because that's the difference between 5V and 3.6V?

@george: I hope you won't mind; it's still a series/shunt implementation...
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Old 25th July 2013, 11:40 PM   #5076
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Cedric, I've looked at that page before; my impression is that the circuits are nice in theory, but they aren't adequate for a stereo potentiometer -- to control four different LDR devices with precision and minimizing the effects of temperature on the device.

Here is an article on LEDs that I found useful -- it explains the relationship between voltage, current, temperature, and light output in an LED, and I feel that one really needs to understand this relationship in order to make progress toward creating an effective control circuit.

LEDs Magazine - Driving LED lamps - some simple design guidelines
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Old 25th July 2013, 11:53 PM   #5077
udailey is offline udailey  United States
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To address the S shape I think you would have to build the circuit almost twice. Basically build a circuit for the series and another for the shunt and program the arduino to give X frequency to Series when Y is given to Shunt or something similar. Maybe a lookup table so that it measures the frequency given to one LDR and then looks up what the frequency should be for the other LDR. If you can program this would be a good way to do it. An even better way would be a circuit that builds this table automatically. Fun!
Wish I could help more but programming is not my strong suit.
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Old 26th July 2013, 07:43 AM   #5078
cedricb is offline cedricb  Europe
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Quote:
Originally Posted by wapo54001
Here is an article on LEDs that I found useful -- it explains the relationship between voltage, current, temperature, and light output in an LED, and I feel that one really needs to understand this relationship in order to make progress toward creating an effective control circuit.

LEDs Magazine - Driving LED lamps - some simple design guidelines
Thanks for the article.

Quote:
Originally Posted by udailey
To address the S shape I think you would have to build the circuit almost twice. Basically build a circuit for the series and another for the shunt and program the arduino to give X frequency to Series when Y is given to Shunt or something similar.
Yes I've already tried with the following diagram (which we already talked via PM) but I couldn't get a descent response curve which I could reproduce/follow. The LDRs are not precise over time! If you apply the same voltage at two different periods then you are getting two different resistance values which are maybe close but not enough to have a match with a margin of errors. Basically the response curve drift over time to the left or the right...
Maybe I'm a bit too picky and I should "trust" your matched LDRs and use the same voltage for both channels; doesn't matter if the attenuation is different over time!

Quote:
Originally Posted by udailey
Maybe a lookup table so that it measures the frequency given to one LDR and then looks up what the frequency should be for the other LDR. If you can program this would be a good way to do it. An even better way would be a circuit that builds this table automatically. Fun!
Wish I could help more but programming is not my strong suit.
I'm a software developer so I'm OK with that, it's just with the hardware which I'm lacking a bit...
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Old 26th July 2013, 02:37 PM   #5079
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One thing I was wondering, but have not gotten around to testing, is how the resistance varies with input signal amplitude. Has anyone explored this? The last time I measured, it was quite well behaved over the audio frequency range.
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Old 26th July 2013, 09:10 PM   #5080
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Originally Posted by soongsc View Post
One thing I was wondering, but have not gotten around to testing, is how the resistance varies with input signal amplitude. Has anyone explored this? The last time I measured, it was quite well behaved over the audio frequency range.
You find a tighter tolerance for the NSL32SR2S (selected), this is why it's a bit more expensive but worth it, it gives typical 40ohm min to 5mohm max.
Where the NSL32SR2 they won't give the typical low figure it can be anywhere with a max to 5mohm.
And the NSL32SR3 is even worse at typical 150ohm min to 25mohm max.

Cheers George
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