LDRs and LEDS

[Flying]

Hello,

Sorry if my searches have not brought up previous discussions about this, but I'm putting together a EQD The Depths that uses LDRs, the ones I've seen recommended are the Tayda's KE-10720 with a Yellow LED, and another suggestion I have read is GL5539s with Green LEDs. I've got some KE-10720s on their way.

What I don't know is what type of LED to use, for example a diffused 5mm Yellow LED has an output of 200mcd and the water clear 5mm Yellow is 2500mcd, quite a difference, and presumably it's important to try and get the right one. From gut shots I've seen it looks like EQD used water clear LEDs, but no idea the colour or what LDRs they used.

Any advice on what LEDs to get in stock would be brilliant, thanks.

[dan.schumaker]

Typically with circuits like that, you want to use diffused LED's (and thats what I used in my Depths build as well).

[Flying]

Thanks, dan.schumaker

I was just lighting up a Red water clear LED and it's are quite directional, so I can see the benefit of the diffused LED. LEDs seem to come in too many flavours, I've just discovered clear super bright diffused LEDs as well as the diffused ones with diffused coloured lenses.

Could you tell me if your LEDs were 'normal' brightness or one of the supper bright variants and what LDRs you used.

Thanks again.

[dan.schumaker]

Thanks, dan.schumaker

I was just lighting up a Red water clear LED and it's are quite directional, so I can see the benefit of the diffused LED. LEDs seem to come in too many flavours, I've just discovered clear super bright diffused LEDs as well as the diffused ones with diffused coloured lenses.


Could you tell me if your LEDs were 'normal' brightness or one of the supper bright variants and what LDRs you used.

Thanks again.

For anything with LDR's like that, I just use the Tayda Green or Yellow 5mm LED's.   I think Orange also works well.

[Marshall Arts]

Get as many as you can get and try, try, try. I build a voodoo vibe and had diffused yellow ones from different sources.. And they all sounded different. Socket them, when you found a good match, pull the sockets out and put the leds in for good. And don't forget to post your findings for the more lazy ones among us (I will build one which I got from M. Kresol soon :-))

[Flying]

Will do Marshall Arts, In my search on here I came across the PCB M.Kresol did... I need to buck up my ideas as he's managed to get it to fit a 125B, my PCB design is a little bigger and will take up a good portion of a 1590BB! in my defense this will be the 4th PCB I'd done the layout for and I'm etching at home.

Putting sockets in sounds to be the way to go.

Thanks again dan.schumaker, I'll add some of Tayda LEDs to my next order.

[Marshall Arts]

Forgot to mention that I ended up using tayda's yellow diffused 5mm regular brightness leds for the voodoo vibe.

[midwayfair]

If you can find the datasheet for your LDRs, you can look at the peak in the spectrum. Many want red light, some yellow, etc. This is a product of the chemical makeup of the LDR. White and blue LEDs will hit any spectrum you need, though.

On the LED side, you want an LED that matches that spectrum as closely as possible, but you also need to account for the current consumption and how that will affect the circuit. In most LFOs, for instance, substituting in a blue LED can cause the waveform to become lopsided, never mind how the extra brightness might affect the curve of the LDR.

I can tell you that very few circuits are going to be designed around anything except red LEDs, because they're cheap and common, and in the old days that was all there was, and if the circuit was based around vactrols, they're almost always built with red or even infrared LEDs inside.

Also, the reason you want diffused is solely that it spreads the light around so that the exact positioning of the LED to the LDR doesn't affect things very much. You can diffuse a clear LED with some sandpaper.

[Flying]

Thanks midwayfair,

The spec sheets gives a minimum and maximum peak spectral resonance of 550nm and 650mn, and the graph looks to peak at 600mn. The yellow LEDs are 590nm, so I think I'm in the ball park, although I'm adding amber to my list of samples to try as they are 605nm.

[Flying]

Okay, I've just ordered:

5mm Diffused LEDs in Yellow, Amber and Green
5mm Water clear LEDs in Yellow, Amber and Green
and 5mm cylindrical water clear LEDs in Yellow, Amber and Green

So that should give me something to play with, both in terms of colour and brightness, and hopefully I'll find something in them that works well with the circuit and the KE-10720.

[madbean]

Depends on the application but for something that does not have strict requirements I use a red diffused LED with a 9203 photocell and it never steers me wrong. But, it really depends on what the opto device needs to do in the circuit. Sometimes the photocell needs a resistor in parallel to control maximum off resistance. Sometimes it needs a resistor in series to control maximum on resistance. Some applications are better suited for extremely fast response times which is when you want to use a device that has the right specs for that.

There's no one size fits all answer, IOW. But, Jon knows what's up (as always).

[alanp]

The other big, BIG thing to know is the resistance range of your LDR.

The Tayda Waitrony unit tops out at 500kohm, IIRC.

Some applications need a 2MOhm or higher LDR.

Check your build doc or similar for what LDR you need.

[somnif]

The other big, BIG thing to know is the resistance range of your LDR.

The Tayda Waitrony unit tops out at 500kohm, IIRC.

Some applications need a 2MOhm or higher LDR.

Check your build doc or similar for what LDR you need.

Yeah, it really depends on the quirks of the circuit. Tayda's LDRs worked well in my Mutron Phasor clone, but the Univibe likes a much higher "off" resistance (seriously, the patent lists "very high value") so I'd need to use a 7532 or 9203'ish sorta deal

[Flying]

Here is an image of the board, I can't seem to get the link to embed

https://www.dropbox.com/s/pof8zuj0c2pag0e/Vibe_01.jpg?dl=0

I ended up using the 5mm diffused yellow LED, I've not tried the other LEDs partly because I completely forgot to socket it! And after trying it I realised it was potentially too bright anyway, and it was the least bright of all my LEDs (200mcd). Don't get me wrong it works and sounds good, but I can distort on the low strings of my strat if the voice knob is wound up high, so I'm currently experimenting moving the LDRs away from the LED, they were touching it to start with, now they are about 1.5mm away, and I think I'll move them further, there is definitely a tonal difference by moving them which I guess it's not surprising as a doubling of the distance will result in 1/4 the intensity, but it's getting too late here to be playing here now.

[somnif]

The 10720 LDR has a peak absorbance around yellow-orange (~600nm). The 5549 I've seen suggested peaks around green-yellow (540nm).

The 10720 has a 10k-500k (approx) resistance range, the 5549 is 100k-10M.

What sounds best? No idea, I've never socketed one and swapped things in and out to see how they sound. If you like the way it sounds with what you have in there, run with it (for the record the Univibe had the LDRs set flat on the PCB surface around the light with a shield over the cluster). Personal preference is the final word in what is "best".