lm324 comparitor

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The microcontroller i am using has no comparitor. So i had to use a comparitor for defining the logic levels 1 and 0. And 89c51 has no A-to-D converter in it. It its so i would have no problems.
 
Hello???? I asked "what's connected to the input of the comparator [that needs comparing], and got the reply:

Quote:
Originally Posted by neo_star
i am interfacing using a comparitor and i am using atmel 89C51.
It does not have a comapritor.

So are you saying you are interfacing a 'comparitor', via a comparator to your 89C51?

I'm confused now! Normally you connect into the comparator input, a transducer of some kind (what I was asking about). But I've not heard of a comparitor connected to the input of a comparator. What kind of signal does a comparitor provide to the comparator?

Maybe you don't need a comparator at all and you can just send signal to the 89C51's A-to-D converter instead, and do the comparatoring in software?
 
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The non inverting input is connected to a light sensor and the inverting input is connected to a reference voltage of about 1v.
 
neo_star said:
The non inverting input is connected to a light sensor and the inverting input is connected to a reference voltage of about 1v.
Click to expand...

Maybe you don't need a comparator at all and you can just send the lightsensor signal to the 89C51's A-to-D converter instead, and do the comparatoring in software?
 
Does the op-amp comparator work on its own without the light sensor by varying the voltage on the non-inverting input?
 
marcbarker said:
Maybe you don't need a comparator at all and you can just send the lightsensor signal to the 89C51's A-to-D converter instead, and do the comparatoring in software?
Click to expand...

89c51 has no built in A to D converter and i need to interface some 6 light sensors to the microcontroller. So if i use 6 A to D convertorsit would be impractical. It would also be impractical if i use single A to D convertor and multiplex it to the 6 sensors because i have deal with complex programming.

i think i answered ur question
 

Oh! I thought 89C51 had a muxed ADC inside it. Well that told me. I sincerely apologise for shouting earlier.

Just wondering, can you use the input threshold voltage of the 89C51 as a 'comparator', instead of a discrete external comparator? It wouldn't have hysteresis (unless you coupled an '51 output back into input via a resistor)
 
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Well thats ok
 
[can you use the input threshold voltage of the 89C51 as a 'comparator', instead of a discrete external comparator? It wouldn't have hysteresis (unless you coupled an '51 output back into input via a resistor)]

if you're concerned about the inputs with mid-range voltage on them, you can reduce (alleged) stress by pulsing the 6 LDRs common with an '51 output when you want to read them, then drop the output back when finished.
 
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What's a light deductor? I googled "light deductor" and there's no results.

Do you mean a photovoltaic device? CdS cell? silicon sensor? Or are you using an LED as a light sensor?
 
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He is using an LED as a light detector. Its output is very low at a few millivolts.
 
Why were there no results when I googled "light deductor" ?

I cut and pasted what you wrote, so I definately didn't mis-spell what you'd wrote
 
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You know you can use an LED detector in 'short circuit mode' if you'd rather not be dealing with mV. You might find it easier.

Just connect LED between the - and + input pins of the 324. Ground the + pin.

The opamp becomes a transconductance amplifier or summit like that.

Feedback resistor between output and - pin sets the sensitivity.
 
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