Unipolar DAC signal to bipolar DAC signal

[strokajm]

I'm interested in setting up a DAC that's bipolar and unipolar.  If it's set for 0-5V unipolar, how do you add a circuit to give a bipolar output of -2.5V to 2.5V??  It seems that it must be a type of voltage divider and/or inverter??  My analog electronics is limited, so any help would be greatly appreciated.

Thank you.

[E Murphy]

Hi strokajm:

You need an OP amp (a 741 will do) connected as a summing amplifier. Connect pin 2 to 6 using a 10k ohms resistor. Pin 3 to ground. Now connect two10k resistors in series to pin 2. Connect them to a  -5 V source. This will give you +2.5 at pin 6. Now connect another 10k resistor to pin 2 and feed the AO signal. With 5 volts you will have -2.5 V at the output (pin 6 = +2.5V + (-5V) = -2.5V) With 0 volts you will have + 2.5 V. Notice the logic is inverted. You can invert it before in software.

You will need +-12 volts or so to power the OPamp (pin 7 +, pin 4 -) Derive -5 volts from the -12 volt supply using a voltage divider or a resistor (1k and a 5V Zener diode)

Regards

Eduardo Murphy