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Old 11th March 2013, 05:59 PM   #5011
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Originally Posted by udailey View Post
No. You want to measure the resistive portion. The two LDRs create a voltage divider and by dividing the voltage of the signal you increase or decrease the volume. Since you have a volume problem we can look at the resistance here and see if its directly associated with the ldrs. So use your dmm leads on the long leads of the LDR. One DMM lead on each LDR lead. Just measure one LDR at a time. I dont care what the measurements are as much as I care that they actually change when you change the volume pot.
Ok, thanks. I'm getting measurements from all LDR's except 'left in' (one leg linked to left out). The other LDR's all change in measurement in relation to movement of the volume pot.

I've got a couple of spare LDR's if needed.
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Old 11th March 2013, 06:13 PM   #5012
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just measured DCV from OV to the positive side of LDR (which i assume is the small lead, but not the dot) - all measure about 1.5 but again 'left in' is dead.
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Old 11th March 2013, 06:24 PM   #5013
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Kristeva, I have just sent you a PM.

Best regards - Rudi_Ratlos
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Old 11th March 2013, 07:03 PM   #5014
udailey is offline udailey  United States
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The dot only involves the negative side of the LED and has nothing at all to do with the resistive side of the LDR as a resistor does not have a plus and minus or positive/negative side.
So you got 1.5V. I get 1.55 so thats fine. Odd that resistance is not changing on this one but you have voltage across it and its the right voltage.
So is this resistance you measured that did not change across one single LDR, Lin to Lout, or is this from Lin to Signal Ground? We should check each LDR individually.
Okay so I will assume it was just one LDR that was not moving. Was its resistance in the Megohm range?
I will also assume its the series LDR which means the signal comes in this LDR and goes out to Lout. Please turn off the lightspeed and measure the resistance from the problem LDR's LED positive lead. Measure between this lead to where the two gangs of the volume pot meet with that one small wire. While measuring turn the volume pot. Do you get between 100 ohms and 100k ohms or do you get just a real high resistance that doesnt change much? I'm trying to find out if there is a problem between the LED side of the LDR and the volume pot.
One more thing. Measure from the negative (dot) LED lead on the LDR to 0V. This must be about 0 ohms or this might be the problem.
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Old 11th March 2013, 09:01 PM   #5015
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Originally Posted by udailey View Post
The dot only involves the negative side of the LED and has nothing at all to do with the resistive side of the LDR as a resistor does not have a plus and minus or positive/negative side.
So you got 1.5V. I get 1.55 so thats fine. Odd that resistance is not changing on this one but you have voltage across it and its the right voltage.
So is this resistance you measured that did not change across one single LDR, Lin to Lout, or is this from Lin to Signal Ground? We should check each LDR individually.

The dead LDR is the 'L IN / L OUT' - on your old drawing that I posted earlier its the LDR 2nd from the right, or 3rd from the left. The other 3 LDR's were fine and moved accordingly with the volume pot.

Okay so I will assume it was just one LDR that was not moving. Was its resistance in the Megohm range?

Even with my DMM set at '2M' I got no reading.

I will also assume its the series LDR which means the signal comes in this LDR and goes out to Lout. Yeah, I think so.

Please turn off the lightspeed and measure the resistance from the problem LDR's LED positive lead. Measure between this lead to where the two gangs of the volume pot meet with that one small wire. While measuring turn the volume pot. Do you get between 100 ohms and 100k ohms or do you get just a real high resistance that doesnt change much?

I'm afraid the problem LDR is again unresponsive on the meter. The other 3 LDR's function exactly as you describe above - between 100 ohms and 100K ohms.

I'm trying to find out if there is a problem between the LED side of the LDR and the volume pot.
One more thing. Measure from the negative (dot) LED lead on the LDR to 0V. This must be about 0 ohms or this might be the problem.

With the DMM on lowest setting (200 ohms) I got a reading of 00.8

P
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Old 11th March 2013, 09:02 PM   #5016
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Kristeva, I have just sent you a PM.

Best regards - Rudi_Ratlos
PM answered Rudi.
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Old 11th March 2013, 10:19 PM   #5017
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Uriah, I found the problem at last whilst going back over some of your tests - faulty 100K resistor leading to 'L IN'. All working well now, sounds great. Thanks for all your help - much appreciated. I've learnt a hell of a lot over the last few days.
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Old 11th March 2013, 10:28 PM   #5018
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in fact, sounds bloody awesome. I knew there was a reason why i did this.
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Old 12th March 2013, 03:57 AM   #5019
udailey is offline udailey  United States
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It was either a dead LDR, messed up trimmer or messed up resistor. Glad you found it. I still havent heard anything that beats LDRs. Its by a mile to!
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Old 13th March 2013, 02:09 PM   #5020
Bibio is offline Bibio  Scotland
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i had a thought. ok i know nothing but i struck me that why use 2 led's to emit when you could use 1 luxeon star and 2 LDR's (for left/right) above the luxeon all encased in one housing. the luxeon would heat both LDR's at the same time to keep them stable and all one would need to do is match the actual LDR's. or do the LDR's come as one component with the emitter already in the casing?
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