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Silonex LDRs for Lightspeed Attenuator

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#182
mmm. Seems I damaged my first set of LDRs - all was going fine until I had a short with a damn ground wire on the back of the pot. Took out a LM317!🙁

Now when I take resistance readings off the series pair, they differ pretty wildly and although I can bring them back together, when I move the pot to a different setting, the resistance again separates. I suppose I should go check out the pot as well as it was there that the short happened.

So anyways, is there a spare set available Uriah?


Fran
 
#183
GUYS and GALS
I suggest wiring up your Lightspeeds with LEDs first. Then see if your circuit works.
EVERYONE dont forget your series resistors that limit current.
Fran, Sorry about that. You seem to be one of a few that have shorted or otherwise fried the LDRs. They are pretty sensitive to current and a little sensitive to voltage, though not as bad. If you go overcurrent they are cooked. Fran I am so much NOT into matching some more. I have a few leftover but I want to make sure everyone gets their packages before letting those go and like I have said I will do matching again in a month or so, but on a less grand scale.
Would you like some bulk LDRs? They are from a new batch and I have not yet tested even one. So unsure yet but am betting they will be perfect with the 100k pots again.
Uriah
 
#185
I am not sure how long a battery would last. My first matching I used a battery and it lasted a week with 10 LDRs on it for most of each waking hour. I then stopped using it but it was not out of juice. Why not try getting ~5V with a battery or several batteries and just use that? If it burns up pretty fast then you can decide to use a power supply, but I would definitely give batteries a try. You might notice the image sliding to the right or left when the batteries start to die as they LDRs wont match as well at different voltages. You can still make a full blow supply with batteries or simply use only batteries but either way dont forget your series resistors.
Uriah
 
#186
I have been using 2 x 6v SLA's feeding into a regulator and I find this lasts for several weeks; I use two pairs of batteries as each battery takes about a day to recharge. Uriah is correct about the wandering once voltage gets too low. George recommends a 12v LI battery - this is smaller than the SLA's and I do not know how long it lasts but if it is good enough for George .....

Alan
 
#188
AndrewT said:
Hi,
what about 5 NiMh per polarity.
Cheap and easy to charge.

But DO NOT use a shunt regulator with small batteries. Shunts would guarantee fast discharge.
Click to expand...


Andrew,

I will try one of Paul Hynes series regulators in that case - thanks for the info.

Would I be correct in thinking that you are suggesting using 5 NiMh without any regulation?

Alan
 
#189
The reason that the LDRs start to wander once the battery discharges is that they are matched at 5VDC and I think this is important. I think if I matched the same exact batch at 2.5VDC then different LDRs would match that had never matched before and the matches I had previously found wound not match as well. So I would suggest 4AA batteries as a start since they will give you 5.2VDC. I like the battery idea. At least we can start building our own battery chargers 🙂 Not a lot to tweak in the lightspeed circuit but that could be some fun.
Here is a massive mAH battery.
http://www.allelectronics.com/make-a-store/item/NCB-4500/NI-CD-RECHARGEABLE-D-CELL-4500-MAH/1.html
Uriah
 
#191
The LDR is one package with 2 different elements. First element is an LED and the second is a resistor. The LED shines with X amount of brightness and we get X amount of resistance. The LED shines with X+1 amount of brightness and we get something like X-1 amount of resistance. More resistance with less brightness, less resistance with more brightness.
SO if you make your power supply and hook up the pot then take the pot and connect it to LEDs rather than to LDRs you will be regulating the current going to the LEDs and making them brighter or dimmer. If, when you turn the pot to the right two LEDs get brighter and two LEDs get dimmer then its working. If anything else is happening then its not working. However the LEDs will be real dim and even not visible in brightness with real high resistance in the pot so only at both extremes of the pot will 2 LEDs be bright and anywhere in between you probably wont see them light up. BUT these two extremes should show you that the circuit is working SO FAR and will keep you from damaging your not so cheap and very hard to come by LDRs if you circuit happens to be wrong. Obviously this experiment has nothing to do with the audio lines, right now we are only making sure you can dim an LED with your circuit and we are also making sure that you are not going to fry your LDR. Please remember that some LEDs will take a whole watt or more and while you could try these to test your circuit you might still fry your LDR since it can only handle .02A or 20mA. So get the cheap Radio Shack LEDs to use in this test and remember your series 100Ohm resistors.
Does this make more sense? We are just trying to test the circuit with LEDs so that if its wrong we fry 10 cent LEDs and not $40 LDRs.
Uriah
 
#196
udailey said:
The LDR is one package with 2 different elements. First element is an LED and the second is a resistor. The LED shines with X amount of brightness and we get X amount of resistance. The LED shines with X+1 amount of brightness and we get something like X-1 amount of resistance. More resistance with less brightness, less resistance with more brightness.
SO if you make your power supply and hook up the pot then take the pot and connect it to LEDs rather than to LDRs you will be regulating the current going to the LEDs and making them brighter or dimmer. If, when you turn the pot to the right two LEDs get brighter and two LEDs get dimmer then its working. If anything else is happening then its not working. However the LEDs will be real dim and even not visible in brightness with real high resistance in the pot so only at both extremes of the pot will 2 LEDs be bright and anywhere in between you probably wont see them light up. BUT these two extremes should show you that the circuit is working SO FAR and will keep you from damaging your not so cheap and very hard to come by LDRs if you circuit happens to be wrong. Obviously this experiment has nothing to do with the audio lines, right now we are only making sure you can dim an LED with your circuit and we are also making sure that you are not going to fry your LDR. Please remember that some LEDs will take a whole watt or more and while you could try these to test your circuit you might still fry your LDR since it can only handle .02A or 20mA. So get the cheap Radio Shack LEDs to use in this test and remember your series 100Ohm resistors.
Does this make more sense? We are just trying to test the circuit with LEDs so that if its wrong we fry 10 cent LEDs and not $40 LDRs.
Uriah
Click to expand...


OK - I think I've got it. For testing 1) don't put the LDR in the ckts at all, 2) just put el cheapo LEDs into the ckts where the LED positions of the LDRs would normally be and see it lite up or not, 3) audio portion completely out of ckts, 4) crank pot and watch in amazement 🙂 .

Sounds easy-peasy.

Thanks,
 
#197
sandbasser said:



OK - I think I've got it. For testing 1) don't put the LDR in the ckts at all, 2) just put el cheapo LEDs into the ckts where the LED positions of the LDRs would normally be and see it lite up or not, 3) audio portion completely out of ckts, 4) crank pot and watch in amazement 🙂 .

Sounds easy-peasy.

Thanks,
Click to expand...


Bingo 😀
 
#198
Does the current through the four LDRs (led side) pass through the variable resistor?

If yes, then a 100k 1W pot has a current limit of 3.1mA and a 500k 500mW pot has a current limit of 1mA. This will limit the minimum usable resistance of the 500k 500mW pot to ~ 5k.

Any ideas about how to get down to the low end without overloading the pot track?
 
#199
Andrew,
I matched them using 500k pots.
Maybe I need more explanation of the point you are making.
At 10mA, half of their max, they hardly start to move in resistance. Its when you get down below a milliamp that the resistance really starts and even connected in series with a 1MegOhm pot you can still vary resistance on the LDR so the tiny amount of current still has the LED lit.
Uriah
 
#200
Tinitus I dont see why the 500k log pot on that page wouldnt work. Should work fine. Like I have said I have not tried a single pot to work all 4 LDRs but in theory it is no different than using a dual gang pot as long as series resistors go from pin A on the pot and shunt goes from C while 5VDC goes to B. Or switch A and C if its to loud at turn on.
Half watt is fine. More than enough.
That power supply is the exact one I use for matching, so yeah, good one to use. Its very very stable as well. Gave me 4.96VDC and I never saw it waiver.
Uriah
 
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