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Old 27th June 2010, 07:22 AM   #3331
fbee is offline fbee  Germany
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Default soldering

...just thought if I can easily avoid burning the LDRs, when I solder them as long as they are in ice-cold water.

I would provisonally fix them on an empty pcb, turn the pcb upside down, put the pcb (LDRs then on the downside) on a cup, that´s filled with ice-cooled water. The soldering side of the PCB remains out of the ware and dry. Leave them in the cold water for some minutes to allow the inner part of the LDRs to be "precooled" to 2C or so.

Some developing heat on the part between soldering point and LDR would be taken by the water. Nevertheless, still keep the soldering process as short as possible.

Afterwards, dry it to avoid corrosion.


Cheers , Frank
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Old 27th June 2010, 09:35 AM   #3332
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Jeez, don't go psycho over these little things - they are a bit sensitive but if you're fairly quick, no problems at all - those heatsink clips are available everywhere, or make your own and are perfect for "nervous Nellies" like me - just do one leg of each device at a time and go onto the next one, then the next, etc and then come back to the first one, etc - it gives each one max cooling time - clean solder it, don't hesitate and don't go over it to make a perfect joint unless absolutely necessary - I understand that the lead free solder is a bit more difficult to use until you get used to it (I prefer the bad ol' lead stuff with a dash o' silver).
- great little devices.
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Old 28th June 2010, 09:16 AM   #3333
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Quote:
Originally Posted by jameshillj;
Jeez, don't go psycho over these little things.

2nd that one, just have a good technique a temperature controled iron, and be quick about it.

Cheers George
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Old 5th July 2010, 02:00 PM   #3334
kffern is offline kffern  Australia
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Hi,
I am using dvb-projects board and I have fitted the matched LDR pair to input and shunt instead of to the 2 inputs.
With the pot turned fully clockwise I read 83ohm across the LDR and
full anticlockwise I read 9.8Kohm and have managed to roughly balance the 2 channels.

Connecting to a chipamp and a portable cd via headphone outputs I get very little change in volume. Fully counterclockwise is about listening level and full clocwise a bit louder.

Would swapping the LDR's fix the problem? I feel I would probably destroy the LDR when I remove them. Also, would the higher resistance pair be used for the input or shunt. I had to remove the paper stuck to the legs so don't even know what the readings were anyway so this has turned into a bit of a stuffup. Knowing the above might help my next attempt.

Thanks,
kffern
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Old 5th July 2010, 06:46 PM   #3335
udailey is offline udailey  United States
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If you got your LDRs from me then, more recently, all 4 are near matches. 2 pair that are close to identical. I tend to think something more is wrong than just the LDRs in the wrong spots. I feel you may hurt the LDRs when removing them as well, but if you use a lot of flux, a very clean iron, a hot iron ~30W or so.. I think you can remove and swap the two you need to switch. Still, it seems something else is wrong.
Uriah
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Old 5th July 2010, 09:29 PM   #3336
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This is why it is always good to use 2 x 8 pin DIL IC socket to mount all the LDR's into without soldering, then when your 100% satisfied and calibrated you solder them into the DIL scockets. Then hard wax the LDR's and socket all together in a neat square block.

Cheers George
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Old 6th July 2010, 12:47 PM   #3337
kffern is offline kffern  Australia
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Here is a picture of my board. The only thing I can think of are the 1k pots being the right way round and the 100k pot wired correctly. The 100k pot is wired so that it would fit onto the board pins. Its from Jaycar in Aus.

The pot is getting 5 volts and varying it changes the voltage from 0 to 5.
I was very carefull with soldering the LDRs. Used a crocodile clip on the legs and very little heat.

Thanks,
kffern

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Old 7th July 2010, 07:21 PM   #3338
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Quote:
Originally Posted by udailey View Post
If you got your LDRs from me then, more recently, all 4 are near matches. 2 pair that are close to identical.
Uriah
I received my shipment of (unmatched) LDRs, but haven't started playing with them yet.

Is the differences between devices best characterized mostly by different slopes, or does the 20ma/40ohm relationship and temperature coefficient vary between devices as well?

Looking at the Silonex PDF, it says that 40 ohms is the MAX resistance at 20ma. Does that, at least, hold true? What is the most typical resistance at 20ma?
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Old 7th July 2010, 07:45 PM   #3339
udailey is offline udailey  United States
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I dont run them at 5V anymore so my current is different but I also dont run them lower than 40Ohms. George and I differ on opinion here if I recall but my experience has been that they WILL go lower than 40Ohms but that when driven lower the resistance curve permanently changes. I have had an LDR explode at 25Ohms but I also have a Lightspeed I built that sits at 25/27 Ohms for shunt at min volume with no problem. LDRs are funny things that are each unique. Some can handle more than others. 40Ohms is my rule of thumb.
The difference between each LDR is the curve. This is what we try to match. Dont worry about temp. Yeah it might be slightly different between devices but it doesnt matter til high resistance and at high resistance the difference made by temp wont move your stereo image a bit.
20mA at 5V if I recall will give around 30Ohms. Fine for some LDRs, not fine for others. Dont try to typify the LDRs. Thats the problem.. none of them are typical. If they were no one would have to match them. Been a long time since I tested at that level. But here is an example. Recently on a test at 11V with .5mA I got measurements from 200R to 1500R. LDRs cant be pinned down to a 'typical' operating characteristic.
So anyway in matching yours why dont you just use a pot and take one down to 100Ohms or so, then measure the resistance of the pot and use that resistor value for your lowest measurement in matching. This way you know how they act at near lowest resistance and yet you dont fool with their resistance curve. Trust your own measurements and experiments. Silonex removes more crap from their website every few months. I expect they remove it as people show them how their datasheets are full of you know what. I have sent them literally thousands of measurements and a handful of junk LDRs to prove my point that their datasheets are not sound and that their manufacturing suffered when they changed manufacturing plants but they just try to steer me to using other optoresistors they make.

Uriah
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Old 8th July 2010, 01:32 AM   #3340
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Originally Posted by udailey View Post
I dont run them at 5V anymore . . .
Uriah
Thanks for that info, I have a somewhat clearer picture now.
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