Well, if you're going to get "clever" like that, you can also do the following (you need a little understanding about Op Amps and how to use resistors and feedback to add (or subtract) two voltages and how to "multiply" (or amplify) by 4.
Assume you want a signal that goes from -10v to +10v, and you have a USB 6009 that only goes from 0 to 5v. You want 0 v from the DAC to become -10v, and +5 from the DAC to become +10v. To simplify the thinking, I'm also going to assume your "signal" goes from -10 to 10, so you'd "ideally" send it to a DAC that goes from -10v to 10v.
So what do you have to do to your signal? Well, you can transform [-10, 10] into [0, 5} by dividing by 4 ([-2.5, 2.5]) and adding 2.5 ([0, 5]). Send this to the DAC. Now build a circuit that subtracts 2.5v (you can use AO1 to generate a +2.5v signal, and make your op amp do the subtraction) and amplify the result by 4. Presto, the output goes from -10v to +10v. It needs a few resistors (3?), an inexpensive op-amp (do people use 741's anymore?), and an appropriate power supply (±15v, probably).
Bob Schor
