Ldr for experimentation

[Kipper4]

Those of you who have rolled your own vactrols.
Perhaps you can tell me if I'm in the right ball park with these please



http://www.ebay.co.uk/itm/2x-10pcs-Light-Dependent-Resistor-LDR-Photoresistor-GL5528-Lab-Supplies-/400470101957?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item5d3de0cfc5

[armdnrdy]

Rich,

It depends on what you want to use them for.

Vactrol based phasers generally use a slower decay time. VTL5C3 type.

I generally keep an assortment on hand for experimentation to find the one that works best for the given circuit.

[mth5044]

They are LDRs, yes, but it really depends on what circuit you are looking at. If you link us to a project it would be helpful.

[Mark Hammer]

Larry is quite on point by emphasizing the response speed as more appropriate to some circuits than others.  Fast responding LDRs will work for anything, because you can always slow them down, but for things like limiters, one needs quick ones.

But the thing to remember about LDRs is that they ARE just resistors.  As such, within certain reasonable limits, you can always alter the circuit to make the LDR work.  You can put fixed resistors or trimpots in parallel with them if the resistance is too high.  You can change cap values to achieve the same corner frequencies as would be gotten with the "ideal" LDR, and so on.

As long as these aren't something that ranges from 5k-off to 40R-on, or 20M-off to 8M-on, or something that idiosyncratic, you should be fine.

[Kipper4]

Mutron iii  ,compresor dod something,
I'll probably go back and look for more then.
I noticed the tayda ones have 680nm after them. Is that the response time?
And thanks guys

[armdnrdy]

My last round I bought this assortment:

http://www.ebay.com/itm/NEW-70pcs-7values-Photo-Light-Sensitive-Resistor-Photoresistor-Assortment-Kit-/291016627224?pt=LH_DefaultDomain_0&hash=item43c1f15418

The Waitrony that Tayda sells has a very fast response. Great for some things....bad for others.
I recently used it for the Mutron Flanger build. It's part of the pedal control voltage circuit.

The radio shack 5 piece pack has a few LDRs that I've found best for some things.
I believe that I used one for a modulation circuit that I added to a delay build.

[tubegeek]

Mutron iii  ,compresor dod something,
I'll probably go back and look for more then.
I noticed the tayda ones have 680nm after them. Is that the response time?
And thanks guys

nm = nanometers

It's the wavelength of the light that they are most sensitive to - each type of LDR has a sensitivity spectrum - where did I just see a graph of this???

I'd guess GEOFEX but I'm not sure.... I saw that graph literally yesterday surfing the web.
You will also be able to find the best matching LED with that specification, it is provided for each type of LED on its data sheet.

EDIT: here you go - look way down towards the bottom of the article. Looks like RED is the best match for 680 nm. Be prepared to spend some time on this site, it's VERY cool.

http://www.ozvalveamps.org/abcdbox.htm

[samhay]

I have had good luck with LDRs from bitsbox (http://www.bitsbox.co.uk/sensors.html; halfway down the page) and Maplin, who have a suprisingly large selection if you are willing to pay well over the odds.
It is nice to vactrols sometimes, so you know you may be able to build another circuit that behaves in a similar fashion. Farnell stock the silonex vactrols in the UK, which seem to be the best bang-for-back: http://uk.farnell.com/jsp/search/browse.jsp?N=2031+203598&Ntk=gensearch&Ntt=silonex&Ntx=mode+matchallpartial

[R.G.]

They're fine for audio experimentation. They're fast, and medium range, and cover a range of resistances that are useful in pedals. They're not particularly great at any one thing, but they're an OK compromise.

The seller is clueless. They're a "trading company", who do nothing but sell stuff other people make. Nothing particularly wrong with that, as that's what most retailers do, but don't depend on their technical information a whole lot. The clues I picked up from the link are that they also sell things like pink princess clothes hangars for Barbie dolls  - and list battery clips in the "dolls and bears" section of their shop, as well as the more obvious one of saying LDRs are used in photoelectric conversion of light to electricity.

The 20-30mS response time is good, but not the fastest. 10K to 1M resistance range is good, and useful, but not the widest. In general fast, wide range and stable are competing items for LDRs, much like "good, fast, cheap; pick any two".  LDRs come in resistances that go down to tens of ohms, up to well over 10M, and response times of a few milliseconds with low memory - but not all in the same devices.

Elmer-Perkins had a great handbook on the characteristics and applications of LDRs. I don't know if you can still find one.

As a side note, I find it amusing that so many things we do with effects involve asking "Can I still get [fill in part here]?"

[Perrow]

Just an idea that popped into my head when someone said something like "you want slower vactrols for audio than your home rolled led/ldr would make", couldn't you slow that down with a cap across the led legs? I know just so much about electronics that I can imagine that would work and little enough (and am tired enough) that I can't see what troubles would arise I imagine there would have to be (extra) resistors involved.

[R.G.]

There are always ways to slow stuff down, as Perrow notes. The trick is in getting them fast enough, consistent with other needs.

[armdnrdy]

Agree!

Many useful vactrols have a fast on time and a slow off time to a given resistance. That would be a bit tougher to replicate.

[Kipper4]

gee thanks everyone.
I just got 6 from bits box and the tayda selection box.

I'm sure i'll find something usefull in this lot.
Other things i want to build the lightwah from Dead astronaught.
thanks for the link Tubegeek.
amazing responses thanks for all the help.
I'll be back with more questions soon about what led's to combine with them.
Get ready for the onslaught when i get around to using them
Thanks

[Kipper4]

suggestions for leds are welcome mean time
especially for the mutron iii
dod 280 IIRC
lightwah

[Kipper4]

These ldr's (bitbox) are tiny I was expecting them to be twice the size.

I bought some yellow leds for the Lightwah
http://www.ebay.co.uk/itm/290898891110?var=590118869901&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_2070wt_936

but for the blue ones i have some in stock i'm not sure theyre super brights, The lens colour is blue and diffuse IIRC
will they do in the lightwah please

thanks guys

[Kipper4]

I'm hoping these will be ok for the blue led superbrights
http://www.ebay.co.uk/itm/131074955555?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_4393wt_1047

[samhay]

Are you planning on use the blue LEDs with the LDRs? The LDRs will be most sensitive to a specific colour of light/LED, and it is more likely to be green, yellow or red. A fun way to spend an evening involves determining the light response, where you shine different LEDs at each LDR while measuring the resistance across it with a DMM. You have to keep everything dark, so turn the light off or throw a blanket over the breadboard.

[deadastronaut]

@rich: i used blue for foot, and yellow for lfo...after a LOT of trials..seemed to react best.

though charts might say otherwise....

just make sure you put them both in heatshrink to isolate the light from each other....and yes i have lots of leds too..its way cheaper to buy 50/100, than a few..

plus i was given a few hundred from some guy that gave up on a mass led project...

[Kipper4]

thanks guys
yes i just found this after a lot of trawling through the thread for the lightwah

http://dl.dropboxusercontent.com/u/7464107/lightwah%20layout.pdf

i'm sure the blues and yellows will be fine for this
the yellows should be here in the next few days which is lucky since i made Jon pattons auto only (crying time)layout on perfboard tonight.

Is it still a good idea to measure each ldr with the meter.?
what should i look for?
resistance i know that but what ranges light to dark?

perhaps i should trawl the roll your own thread again.

i thought i'd see how i get on with this one before doing the foowah version.

any tips on experimenting would be handy thanks guys

should i look uo vactrol specs and try to match those with my meter readings.?

are these ldrs a bit like transistors the specs say one thing and the reality can vary wildly?

Oh so many questions

[Kipper4]

The Lightwah
Now this is what I wanted in an auto wah.
Big Thanks to Rob (Dead Astronaught) for the hard work that went into creating this pedal
and also to Jon (midwayfairer) for the auto only (Crying Time) layout.

my roll your own vactrol (super bright yellow 5mm led and Bitsbox LDR) worked without any testing
the circuit has minimal noise.
I added diode on the +9v to ground for polarity protection and a 1M resistor to ground as anti pop protection.

Superbe.
I'm gonna look into the oscillator to use in other wahs too.
thanks to everyone involved for helping me out.

The next big plan is to make the Neutron 3.