My battle with LED attenuation

[Paul Barker]

Could be.

[Mike H]

that pink-shirted, condescending gobshite who says:

"Don't you know you could be due PPI compensation!
Not interested?
Banks have set aside billions of pounds, yet you've still done nothing about it?"

Gives me an overwhelming urge to kick the TV screen

Yep! Damn right

[Mike H]

Apart from the problem of matched devices (or non-matched, that is), which is difficult enough by itself, what I don't like about this is tracking mismatch between the series pass element and the parallel shunt element. How do you get one to have the total chain impedance minus whatever the resistance of the other one is set at?


Some while ago I was thinking about a servo system.

For each variable element, have one light source and two sensors (LDR's).

One sensor is used as the feedback for an op-amp based servo control system that varies the power to the light source.

The second sensor is the actual audio attenuator. (It implies that both sensors must be matched.)

I was literally thinking in terms of a filament bulb and two LDR's in a black tube. (Lamp in the middle, an LDR at each end.)

My idea was that the attenuator resistance should closely track the position of the control pot, as the wiper is actually the input to the servo op-amp, which in turn will force the light output to be whatever it has to be in order to make the LDR's exactly whatever the equivalent resistance has to be to match the control pot (The actual op-amp output to the light source will be far from linear.)

However I couldn't figure out how to combine series and shunt elements. Each will require their own servo drive.

I even tried sim'ing this in LTspice once, but think I got bogged down with difficulties with the lamp model, so eventually abandoned it.

[Cressy Snr]

that pink-shirted, condescending gobshite who says:

"Don't you know you could be due PPI compensation!
Not interested?
Banks have set aside billions of pounds, yet you've still done nothing about it?"

Gives me an overwhelming urge to kick the TV screen

Yep! Damn right

And don't get me started on that damned singing orange.

[Mike H]

Damn you! DAMN YOU!! I had managed to forget ....

[Light Dependant Resistor]

How we match LDR's is to firstly use the NSL32SR2S which is a selected LDR that comes in grades of resistance from A to F, A being strong ie low resistance with applied current and F being weak. So with two say B graded LDR's you get both being similar.

On the AOS forum, and on this forum we offer to upgrade prior boards to the specification shown here. 2k trimpots are installed separating the L and R anodes and the connections that were on the green connector blocks are wired back to a central located 4 port connector block. This enables excellent channel balance, slightly over and above the initial good matching done on prior boards. The kit constructor can also check our initial matching with a multimeter, and refine further if required

If any of our customers require this turn around is 1 day, and we ask postage be paid each way.

Cheers / Chris