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op amp and photo diode

jerk

Oct 13, 2010
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I need to detect room luminosity. I was thinking to use normal LED and op amp to bring the signal to PIC adc.
Will the selected op amp in the below circuit be OK?
 

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Harald Kapp

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No, the 741 will not operate from a single supply with an input signal near ground.
Use a dual supply (e.g. +-5V). You can easily generate -5V from +5V using a switched capacitor voltage inverter.
You may also wan t to use a modern OpAmp with better technical data, as the venerable 741 is rather outdated.
 

jerk

Oct 13, 2010
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No, the 741 will not operate from a single supply with an input signal near ground.
Use a dual supply (e.g. +-5V). You can easily generate -5V from +5V using a switched capacitor voltage inverter.
You may also wan t to use a modern OpAmp with better technical data, as the venerable 741 is rather outdated.

can you suggest some modern op amp where I can use same power supply as for the PIC - 5VDC.
But it has to be large enough I can hand solder it to my PCB (5SOT23 are not an option). I was looking Farnell store and all I could find to be suitable for hand soldering were DIP types, for example MCP6271-E/P.
 
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Harald Kapp

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You can try almost any operational amplifier with rail to rail input and low bias current, e.g. the OP184 or a similar type (Google: rail-to-rail input operational amplifier)
 

KrisBlueNZ

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Nov 28, 2011
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Microchip make a whole range of op-amps that are designed to run from 5V and have rail-to-rail outputs, and often, inputs as well. Look on microchip.com under op-amps.
 
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