lm324 comparitor

[colin mac]

Really you should post a schematic of how you connected everything.

 

[neo_star]

I asked "what's connected to the input of the comparator [that needs comparing], and got the reply:

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

I'm confused now! Normally you connect to the comparator input a transducer of some kind. 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?

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.

 

[marcbarker]

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?

 

[neo_star]

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?

The non inverting input is connected to a light sensor and the inverting input is connected to a reference voltage of about 1v.

 

[marcbarker]

The non inverting input is connected to a light sensor and the inverting input is connected to a reference voltage of about 1v.

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?

 

[colin mac]

Does the op-amp comparator work on its own without the light sensor by varying the voltage on the non-inverting input?

 

[neo_star]

Does the op-amp comparator work on its own without the light sensor by varying the voltage on the non-inverting input?

may be i should do wat u said.

 

[neo_star]

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?

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

 

[marcbarker]

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)

 

[neo_star]

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)

Well thats ok

 

[marcbarker]

[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.

 

[neo_star]

i am using LED as a light deductor

 

[marcbarker]

What's a light deductor?

Does it by chance replace external discrete comparators?

 

[neo_star]

What's a light deductor?

Does it by chance replace external discrete comparators?

the output voltage goes high when the light falls on it but the output is in the range of few millivolts

 

[marcbarker]

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?

 

[audioguru]

He is using an LED as a light detector. Its output is very low at a few millivolts.

 

[neo_star]

He is using an LED as a light detector. Its output is very low at a few millivolts.

yes right its much better than a photodiode

 

[marcbarker]

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

 

[neo_star]

Why were there no results when I googled "light deductor" ? Are you sure an LED used as in this way is called a "light deductor"?

sorry about that its detector

 

[marcbarker]

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.