can I measure negative voltage(-5v to 5v) with ADC804? how?

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tictac

Full Member level 5

Hi
can I measure negative voltage(-5v to 5v) with ADC804 and HOW ?

by Regards.

umery2k75

Yes, its possible.
But this would lower down the 8-bit resolution. You leave ref/2 pin open, don't connect it. If I remember that PIN number correctly, in this you get range from 0-5V.You first takes the absolute value of -5V to +5V, so altogether difference of 10V, means if you give negative voltage, it must be get convert into positive value, if you get positive value it remains the same, now suppose you get scale from 0V to +10V, 0V represents -5V and +10V represent +5V.Scale it down from 0-10V to 0-5V. Now then feed it into your ADC0804. All is done now.
Remember:
1)Add +5V in input, you get range from 0-10V.
2)Divide the range 0-10V with 2

ADC0804, won't know what it means, you will be the one, who must understand what the values means.From 0-2.5V, this means range from -5V to 0V. From 2.5V to 5V means 0V to +5V

tictac

Points: 2

tictac

Full Member level 5

Hi umery2k75
thank you so much
can you tell me about add +5v in input? Can I do this with opamp?

FvM

Super Moderator
Staff member

There are plenty of ADC that measure negative voltage, but they need dual supply, generally.

ADC804 input can be scaled to +/-5 V by two resistors respectively a voltage divider to +5V. The method is discussed in the datasheet for +/-10V input.

tictac

Points: 2

tictac

Full Member level 5

Hi
Is this circuit work correctly? vref pin=open

krt

Points: 2

Staff member

Yes.

krt

Points: 2

Points: 2