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Old 29th November 2010, 03:18 PM   #1
maxw is offline maxw  United Kingdom
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Default Using a Precision Current Source to drive an LDR attenuator

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

Click the image to open in full size.

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...
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Old 29th November 2010, 03:27 PM   #2
maxw is offline maxw  United Kingdom
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I'm thinking something like this. Any pointers?
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Old 5th December 2010, 07:20 AM   #3
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Almost the same concept but less complicate and does not use as many i.c.s.


Quote:
Originally Posted by maxw View Post
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

Click the image to open in full size.

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...
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