[sdiy] LED/LDR modules

[mikko.a.helin at nokia.com]

The on/off ration can also be improved by increasing control current -> more
light -> less ON resistance, and by using four LDR's in series-parallel
configuration. 


> -----Original Message-----
> From: ext Martin Czech [mailto:czech at Micronas.Com]
> Sent: 14. February 2001 11:54
> To: mikko.a.helin at nokia.com
> Cc: synth-diy at node12b53.a2000.nl
> Subject: RE: [sdiy] LED/LDR modules
> 
> 
> This will usually not help, since you are interested in on/off ratio,
> not in absolute value. You could think about a LDR divider, with two
> LDR (upper and lower leg), driven by LEDs connected to eg. some
> difference amplifier, constant current. This way the ratio problem
> can improve a little bit, of course not usefull if you really
> need a *RESISTOR* effect.
> 
> The crazy thing about LDRs is that the increasing resistance (light
> off) leads to slow carrier removal, which in turn slows down
> the resistance growth. There seems to be no significant recombination
> like in photo diodes or transistors. The lack of 
> generation/recombination
> may be OTOH one reason for the observed low noise. I guess zener noise
> is due to generation (at least a good part).
> 
> m.c.
> 
> 
> :::X-Authentication-Warning: node12b53.a2000.nl: majordomo 
> set sender to 
> owner-synth-diy at node12b53.a2000.nl using -f
> :::From: mikko.a.helin at nokia.com
> :::To: synth-diy at node12b53.a2000.nl
> :::Subject: RE: [sdiy] LED/LDR modules
> :::Date: Wed, 14 Feb 2001 11:11:55 +0200
> :::
> :::Don't know about black holes, but if you put couple of 
> LDR's in series the
> :::decay time to certain resistance value will drop 
> proportionally depending on
> :::the number of LDR's put in series.  Still quite slow.
> :::
> :::-Mikko
> :::
> :::
> :::> -----Original Message-----
> :::> From: ext harry [mailto:harrybissell at prodigy.net]
> :::> Sent: 13. February 2001 21:57
> :::> To: danial stocks
> :::> Cc: synth-diy at node12b53.a2000.nl
> :::> Subject: Re: [sdiy] LED/LDR modules
> :::> 
> :::> 
> :::> All LDR have the same principle... you can blast them 
> with unlimited
> :::> photons and get the resistance to drop very fast... but then 
> :::> the recombination
> :::> takes its own sweet time.  Cells with lower dark resistance 
> :::> are as a rule,
> :::> faster.
> :::> Very wide resistance ratio cells are, as a rule, slower.
> :::> 
> :::> You need my "Flash_Dark" technology to apply negative photons 
> :::> to eliminate
> :::> this effect.  Be sure to have your circuit properly designed 
> :::> to work properly
> :::> in close proximity to the black hole technology I use...
> :::> 
> :::> Please... no inquiries this time from departments of defense. 
> :::> This is Synth-DIY,
> :::> 
> :::> not DIE !!!
> :::> 
> :::> H^) harry
> :::> 
> :::> danial stocks wrote:
> :::> 
> :::> > I put then some shrink-wrap tube
> :::> > >(it that the correct name for "Schrumpfschlauch" ?)
> :::> >
> :::> > not too sure.. what's "Schrumpfschlauch" ? :0
> :::> > normally called "heatshrink tube" here
> :::> >
> :::> > >Worked OK, LDR resistance can be changed from near infinite
> :::> > >to 2 KOhms (LED current varied from 0...20 mA)
> :::> > >But it is slloooooooowwww...
> :::> > >
> :::> > most of the people who like ldr's I've spoken to like the 
> :::> slowness in them,
> :::> > it's part of the sound I spose.. generally they all will be 
> :::> pretty slow,
> :::> > nothing like close to OTA or other semiconductor device, 
> :::> but then they
> :::> > prolly have different speeds of LDR so maybe you could get 
> :::> a faster one..but
> :::> > it will prolly still be notably slow..
> :::> > maybe the rate of change is proportional to the amt of 
> :::> instantaneous light
> :::> > change.. ie if you blast it with a huge amt of light it 
> :::> will get to a point
> :::> > much more quickly than with a lesser amt of light [so with 
> :::> the high light
> :::> > exposure, it obviously would be a point midway along 
> :::> somewhere, not the
> :::> > stable value for this light lvl].. if this is the case, you 
> :::> could cause a
> :::> > large light pulse to be pulsed when a change occours, 
> :::> speeding it up.. could
> :::> > work ok for interesting manipulation?
> :::> >
> :::> > Cheers,
> :::> > Dan
> :::> > 
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