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[SOLVED] 741 opamp as a comparator

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Hello all

I am trying to use the 741 op-amp as a comparator, I am using single supply operation of 5 Vdc. my problem is that I am getting low output level of 1.6 (not ground which supposed ideally), so I have a problem with logic '0'....
please how can I make it near to zero ?? what I have to the output ???

Note: the output of the comparator will be an input to the 8051 microcontroller

I know using dedicating comparator are more better, but I only have 741

Any help will be highly appreciated

regards
 

A lousy old 741 opamp was designed 45 years ago. Look at its datasheet, it is spec'd only with a 30V supply and some do not work when the supply is less than 10V.
Its inputs might not work if they are within 3V from ground or the positive supply voltage and the output might not go closer than 3V to ground or the positive supply voltage as you see.

Its output might go closer to ground if you add a load resistor from its output to ground, try 390 ohms.

A modern Cmos opamp works from a low supply voltage and its inputs work perfectly between ground and the positive supply voltage. Its output goes down to ground and up to the positive supply voltage if its output load current is low. Sorry, I do not know which ones are available in your country.
 
If you insist using 741 as comparator at 5V supply voltage and output has large enough voltage swing you will have to add a transistor circuit on it's output to achieve 0 to 5V voltage swing needed for MCU. Is it worth doing or is it better to use LM311 comparator?
 
The output stage is not the kind of switching stage you
would prefer for a comparator. You may be able to move
the VOL with a pulldown resistor, probably at cost to
VOH since the whole chip is voltage starved and the high
side is not near-rail-capable either.

If you can get a LM741 you must be able to get a LM339
which is equally antique, but more suited to the task
(with input common mode range including ground, a
saturating switch output and rated at 5V supply).
Unless "only have" is based on making no effort to
acquire.
 
In case you wish to use the 741, you need to power it with a negative voltage at the supply pin. Then output will go down to zero (or within a volt or two of the negative supply whatever it is).

There are ways to obtain a negative supply from a positive polarity. Example, positive pulses from a 555 IC, fed to a network of capacitors and diodes.



Perhaps it is unsafe for the microcontroller input to be exposed negative polarity? You may need to ensure the 741 output does not go below 0V.
 
If you are using a micro , then you can toggle a pin within an interrupt (say 1khz) and generate your negative supply from that as described above , without the 555 part.
 
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