mesamune80

Hi all,

i am using a comparator ic and LM393 ,configured it as windows detector circuit with the output go to LED and pic uC pin.
But i could not read any high logic from the ic output pin when the pin is goes high. i am using a 1k pull up resistor for the power (12v) to LED which is parallel to uC pin as well which i want the uC to detect it is logic high.
Any problem with my configuration?

Gayan Soyza

Remove the comparator part from the uC & check the comparator whether it is working correctly?

Can you see the LED goes on when input logic = 1 (in between your range)?

What input did you feed the input?Inverting pin or for the non inverting pin?

Note that its output open collector type.

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Gayan
Forum Supporter

mesamune80

ya,my LED lit but i could not get any signal to my uC pin.
my circuit is look like this with the VrefA and VrefB to my pic uC pin (input pin)
Is there anything i need to add so that my uC can detect logic 1 and 0 respectively?

Attached Images

Windows Detector1.jpeg (21.4 KB, 49 views)

Nigel Goodwin

Remove the LED's, they are stopping the outputs going high!.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

mesamune80

i see ,thanks nigel ,but i need some indication for that? (high and low limit indication)
can i do it in a different way? or any alternative for that?

Nigel Goodwin

Use a transistor to feed the LED.

Or, more crudely, put a resistor in series with the LED - but this will still restrict the output of the comparator from going fully high, and reduce the LED's brightness.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

ericgibbs

Hi Nigel,
Just noticed he is using a +12V supply to the LM393...

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Eric
"Good enough is Perfect"

PIC tutorials:
Nigel's: www.winpicprog.co.uk/
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

mesamune80

It seem like i got not much choices,either a transistor or a dim LED =_="
what transistor is suitable for this i can use 2N222?

mesamune80

anything wrong with 12V? @_@"

Nigel Goodwin

Not as long as you have a current limiting resistor feeding the PIC.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

mesamune80

okay i'll try it out ,thanks guys.

eblc1388

Or you can use 3.3V 250mW zener diode in series with each LED.

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L.Chung

ericgibbs

hi,
You could do it this way.

I have modified the top LED, I'm assuming a Red LED about Vfwd=2V

The LM393 is open collector output, also the PIC analog is a high impedance.

Attached Images

uC1.jpg (24.9 KB, 29 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Nigel's: www.winpicprog.co.uk/
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

mesamune80

Thanks for all the replies,really thanks for all of you.
i think i might choose either zener or voltage divider method to power up both my LED and also signal to my uC. =)

mesamune80

Can i put it this way? so that i can adjust untill the voltage to my uC is about 5V at the same time i also can light on my LED.
Or any better idea i can use? at the moment i have 10k adj resistor and 1k resisitor.

Attached Images

sample.JPG (22.4 KB, 15 views)