Using a Precision Current Source to drive an LDR attenuator

maxw

Member
2004-06-10 7:23 am
Berlin
Has anyone actually tried using a current source based on digital potentiometer to drive a LDR attenuator? I've seen it mentioned in the massive Lightspeed thread but has anyone actually tried it?
It would be good for folks who want an LDR based attenuator with digital control (for remote control, displays, integration etc).
Is this how the DIY Paradise Eva works?

Anyway, I was looking at this app note from Maxim which shows pretty much the generic current source based on a digital potentiometer and a shunt:
Precision Current Source is Software-Programmable - Maxim

[IMGDEAD]http://www.maxim-ic.com/images/appnotes/3464/3464Fig01.gif[/IMGDEAD]

I want to try it but use a regulated PSU instead of the shunt IC. By using their forumula Rsense should be 200R when using a 5V supply, but I'm not sure what to use for Rs? Can anyone explain what this resistor is for? I'm thinking its to limit the amount of current going through the digital potentiometer wiper as they can generally only handle 1mA...
 

maxw

Member
2004-06-10 7:23 am
Berlin
I'm thinking something like this. Any pointers?
 

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vt4c

Member
2001-01-29 12:48 pm
Malaysia
Almost the same concept but less complicate and does not use as many i.c.s. :)


Has anyone actually tried using a current source based on digital potentiometer to drive a LDR attenuator? I've seen it mentioned in the massive Lightspeed thread but has anyone actually tried it?
It would be good for folks who want an LDR based attenuator with digital control (for remote control, displays, integration etc).
Is this how the DIY Paradise Eva works?

Anyway, I was looking at this app note from Maxim which shows pretty much the generic current source based on a digital potentiometer and a shunt:
Precision Current Source is Software-Programmable - Maxim

3464Fig01.gif


I want to try it but use a regulated PSU instead of the shunt IC. By using their forumula Rsense should be 200R when using a 5V supply, but I'm not sure what to use for Rs? Can anyone explain what this resistor is for? I'm thinking its to limit the amount of current going through the digital potentiometer wiper as they can generally only handle 1mA...