lm324 comparitor


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?
 
Last edited:

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)
 
Last edited:

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.
 
Last edited:
marcbarker said:
What's a light deductor?

Does it by chance replace external discrete comparators?
Click to expand...

the output voltage goes high when the light falls on it but the output is in the range of few millivolts
 
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?
 
Last edited:
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
 
Last edited:
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.
 
Last edited:
You must log in or register to reply here.

Similar threads

Using LM324 and OP07 for controlling voltage
2
Replies
20
Views
7K
MD MUBDIUL HASAN
A
LM324N IR black and white line detector
Replies
7
Views
5K
unclejed613
I
50 Hz oscillator based on a LM324N IC
2 3
Replies
50
Views
17K
iods
I
U
Op-amp, use LM324 for LM741?
Replies
6
Views
20K
upand_at_them
U
D
Bi-Freq Sweep Generator LM324
Replies
0
Views
2K
darryl_co
D
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…