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Using Arduino => General Electronics => Topic started by: sreedevk on Dec 30, 2012, 07:11 pm

Title: Op amp output as digital input
Post by: sreedevk on Dec 30, 2012, 07:11 pm
Hi,
I am planning to provide a 5V output of an op amp directly to a digital pin as input to Arduino Mega. Is there any chance of damaging the board?
Title: Re: Op amp output as digital input
Post by: johnwasser on Dec 30, 2012, 07:16 pm
As long as the voltage is limited to the range 0 to 5V it will not harm the Arduino.
Title: Re: Op amp output as digital input
Post by: sreedevk on Dec 30, 2012, 07:19 pm
Thanks. One more question. If i supply 5V to the output pin of an op amp, will it damage the op amp?
Title: Re: Op amp output as digital input
Post by: winner10920 on Dec 30, 2012, 07:53 pm
Depends on the opamp, if the 5v is coming from an arduino output you may fry the arduino pin first, depends onthe actual opamp, you couldn't go wrong with a 220 -1kohm resistor in between, you'll never have a problem then so long as the opamp doesn't go above 5v, and then a 5.1v zener would fix that
Title: Re: Op amp output as digital input
Post by: dhenry on Dec 30, 2012, 07:55 pm
Quote
If i supply 5V to the output pin of an op amp, will it damage the op amp?


Depending on the opamp, but generally no for small signal opamps and potentially yes for power opamps.
Title: Re: Op amp output as digital input
Post by: johnwasser on Dec 30, 2012, 07:55 pm
I suspect that if you connect the output directly to the 5V supply and the output is trying to drive LOW (0V) you will probably damage the output transistors of the op-amp.  

If you connect through a pull-up resistors you might be OK.  Depends on how much current the op-amp can source or sink and how much current will flow through your pull-up.  A 1K resistor (5 mA current) might be safe.  Depends on your op-amp.
Title: Re: Op amp output as digital input
Post by: Grumpy_Mike on Dec 30, 2012, 11:33 pm
Quote
If i supply 5V to the output pin of an op amp

This begs the question as to why on earth you would want to apply a 5V power line to an output. Connecting outputs direct to a supply makes no sense. What are you trying to do?