Bipolar adc...

[gatas]

Hi there..I am not sure about the exact english word (I think it is bipolar) but i am searching for a simple-cheap adc that accepts input in the range of -5V to +5V...
I had used adc0804 before but i am not sure if it can convert negative input. In the datasheet there is an interface for -5V to +5V signals but they are using a Beckman Instruments #694-3-R10K resistor array, but i dont understand how it works. I 'd appreciate it if somenone could enlighten me on adc0804's ability of accepting negative input, or maybe suggest me another adc. A complementary dac (bipolar again) i could use in conjuction with the adc, would be fine...

Thanx in advance.....

 

[Scubasteve]

gatas,,

The input stage on that converter is just a 10k-10k resistive voltage divider. I think that any two 10k resistors will work, but I am not sure about why they chose that beckman part.. I believe that company has either changed names or went out of business, so I couldn't check the spec. sheet. Just try to use the most accurate resistors you can get..

Steve

 

[acrid_22]

gatas

I think that you should put pin 7(-Vin) to +5V, if you want to read a input from -5V to +5V, but you should need to change the Vref/2 value to +5V.
Im not sure about this, but it would work.

gil

 

[Nigel Goodwin]

It would be unusual for an ADC to cover positive and negative voltages, nor is it required. You simply bias the input of the opamp to +2.5V, a negative voltage will move it down towards zero, and a positive value will move it towards +5V.

It's a simple circuit, you need the output of an opamp that can move between -5V and +5V (10V range), when it's input is zero, then the output should be zero as well. Connect the output of the opamp via a resistor to the input of the A2D, and a second resistor from the input of the A2D to 5V, the two resistor should be identical. Notice that the two resistors do two tasks, they shift a negative to positive swing to a zero to positive one, and also divide by two - converting the 10V swing to a 5V one.

Your software needs to take care of the rest, it's quite straight forward to do.