Hello,
I want to use a photoresistor with voltage divider on to detect the presence of the sun (like night or day), however photoresistor have big impedance regardless the luminosity.
Moreover I saw in datasheet that the ADC wouldn't be load with an impedance >10kohms but I saw some project which exceed this limit...
Does a big impedance influence a lot the result on ADC ?(I don't want to make a luxmeter)
Thanks
Will big impedance on ADC influence result on it ?(photores)
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Re: Will big impedance on ADC influence result on it ?(photo
Yes, very much so, why do you think they publish the input impedance requirement if it wasn't important?Does a big impedance influence a lot the result on ADC ?
How to get around your problem is to use an external op-amp as a unity gain buffer. The output impedance of the op-amp is very low (few ohms) which can drive the ADC input correctly. The very high input impedance of the op-amp is well suited for connection to the photo-resistor divider circuit.
However, if you only require a go-no-go type of indication vs. actual ADC measurement value, it would far simpler to make use of the on-board voltage comparator(s) found on many PIC devices. With a comparator you can set a voltage "trip" point to tell the PIC if it's dark or light based upon whether the photo-resistor voltage drop is above or below this threshold.
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Re: Will big impedance on ADC influence result on it ?(photo
Thanks man for your reply,
Yeah op-amp could be a good option but I didn't want to put other component on this board... I don't know why I haven't thinking to pic comparators
Thanks for your helpful reply
I was thinking this remark was just here for high precision application but it isn't seem like thatYes, very much so, why do you think they publish the input impedance requirement if it wasn't important?
Yeah op-amp could be a good option but I didn't want to put other component on this board... I don't know why I haven't thinking to pic comparators
Thanks for your helpful reply