### Author Topic: Voltage Difference Detector (>100mV) from two different sources.  (Read 9971 times)

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#### hgg

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##### Re: Voltage Difference Detector (>100mV) from two different sources.
« Reply #25 on: March 02, 2014, 09:59:27 am »
Great!  I will order some of them next week and try again.
Thank you!

#### hgg

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##### Re: Voltage Difference Detector (>100mV) from two different sources.
« Reply #26 on: March 03, 2014, 04:06:15 pm »
While waiting for the voltage references to arrive....

In the datasheet of the LM311 there is a way to balance its voltage offset error.  If you can use this
method and instead of balancing it, you make it higher up to 100mV then you can connect the two
input voltages and there you go!  You have a voltage difference detector with just one part.
A dual comparator.  One voltage to one comparator and the other voltage to the other but with its
terminals reversed.
Both voltages to both comparators but with their terminals reversed.

One problem though.   I cannot achieve an out of balance voltage greater than 30mV....

The potentiometers with the closest values I had where 1K and 10K.  The diagram uses a 3K.
Do you think that this might be the reason?

Do you know what is the maximum offset correction that the LM311 can take?
« Last Edit: March 03, 2014, 04:17:51 pm by hgg »

#### hgg

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##### Re: Voltage Difference Detector (>100mV) from two different sources.
« Reply #27 on: March 07, 2014, 06:41:46 pm »
I've tried, but its quite difficult to do it with only the offset error of the LM311.

Anyway, the 2.5V vref arrived and lifting the ground as well with a voltage reference did it.
Perfect rock solid +/- 100mV voltage difference detection!

Thank you guys for your help!

Smf