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Old 3rd September 2009, 09:02 PM   #2431
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Quote:
Originally Posted by Puffin View Post
I bought some cheap unmatched LDRs whilst waiting for the next batch from Uriah.
.
No wonder, I thought you were using what I recomend NSL32SR2S, or NSL32SR2 or if you must NSL32SR3 which won't go low enough in level and are even harder to match, no wonder you have this problem there are so many different LDR's out there their resistance span varies greatly, stick with the NSL32SR2S's and all will be fine.

Cheers George
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Old 3rd September 2009, 09:25 PM   #2432
Puffin is offline Puffin  United Kingdom
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I am using the NSL32SR3's
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Old 3rd September 2009, 10:49 PM   #2433
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There's some of your problem they don't go as low in volume as the
NSL32SR2S.

Resistance Table

Full Light Full Dark

NSL32SR2S 40ohm to 5 megohm

NSL32SR3 150ohm to 25 megohm


Big difference as you can see, also the matching becomes way harder to get four matched together. And when you match 4 together you get a far better logarithmic feel to the volume control, than you do when you only match the series and then the shunts separately

Cheers George
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Old 4th September 2009, 01:52 AM   #2434
alazira is offline alazira  United States
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Puffin,
I was the one who previously posted that adding a 100R to the 5V wiper/input of the pot resulted in a change of the volume curve (keeping the other 100R into the LED). I would be interested to see if others can verify my result.
Garrett
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Old 4th September 2009, 05:17 AM   #2435
Puffin is offline Puffin  United Kingdom
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Alazira. Thanks I will try that.

George. Is it a no-no to increase the values of the shunt resistors?
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Old 4th September 2009, 06:37 AM   #2436
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No problem to increase using 5vdc it just won't reach max or min volume, just don't decrease, this will blow the leds at max and min.

Cheers George
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Old 4th September 2009, 07:08 AM   #2437
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This may help explain it better .

Cheers George
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Old 4th September 2009, 07:23 AM   #2438
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Hi,

1. Can we use a digital pot like DS1669 from Maxim ?

Best regards,
Bins.
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Old 4th September 2009, 12:08 PM   #2439
udailey is offline udailey  United States
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There are a number of good digital pots out there and that one looks quite easy to implement. Remember though that that digipot can only handle 1mA on the wiper so you will have to put a sizeable resistor in front of the wiper to cut down the current. I=V/R
Uriah
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Old 4th September 2009, 12:16 PM   #2440
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Hi,

What current rating is required for the 5V DC supply ?

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Bins.
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