[sdiy] LED/LDR modules

[Martin Czech]

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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