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problem in output of LM 324

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Newbie level 3
Jan 1, 2013
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I am making a project using LDR sensors.
For converting the analog voltage of LDR to the digital one,I am using an LM 324 IC.
I am giving the LDR connection to the non-inverting input of LM324(pin 3) and a potentiometer to the inverting input of the IC(pin 2).
When the voltage at pin 3 > voltage at pin 2(the reference voltage),i should get a digital high output ( i.e.,5 v) and a digital low output in the
other case(i.e.,0 v) on giving a 5v +Vcc supply to pin 4.
But what I am getting is a 3v output for digital HIGH value and a 0v output for LOW.
(There is ,I think,lies the main problem.)

When I am giving the digital HIGH output to the PC ports of ATMega8 microcontroller,the motors connected to PB ports are not getting driven at all.(They should get driven as per my program.)
So Guyz, plz let me know where exactly lies the problem.
Is a 3v HIGH output from LM324 not enough for the microcontroller??

The 3V Voh is specified in the datasheet of the LM324 with Vcc=5V and RL=2kohm. Normally the input level requied is >2.4V for a HIGH level. If you connect 5V to the PC input port and the program does not start - you have problem with the program.

Enjoy your design work!

the output High of your LM324 and the Input Hi of your Atmega are very close limits, and it is very possible you are having some mismatch problem here.
You can try either of these suggestions -

1) try increasing the LM324 V+ power supply to around 7-8 volts. Not more !!
2) use an LM311 instead - don't forget its pull-up of around 1k. For comparator applications it is better to use a comparator chip.

lastly - for such applications it is always a good idea to include some amount of hysteresis in your comparator circuit

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