DEC AXV11-C analog board

[Brent Hilpert]

On 2022-Feb-13, at 9:04 AM, Douglas Taylor via cctalk wrote:
> Stopped fooling with the AXV11 for now.  Applied various voltages to the Data Translation input and recorded the A/D octal values to get an idea of what the calibration of the board is.  It looks very linear, +/-10v range.
> 
> Using a single battery and voltage divider I was able to generate voltages on the input of the DT2762 board, however, I had to swap wires to get negative voltages.  Is it possible to construct a battery driven circuit that will present both positive and negative voltages at the input?  A bridge of some sort?


You said it: what amounts to a wheatstone bridge. Take say, two 10K R, in series across the battery forming a 1:1-split voltage divider. The center point shall be the common/0V. The wiper of a pot across the battery forming a variable voltage divider presents the +/- test signal.

That would give e.g. +/-6V from a 12V battery.
It also presumes you have a reasonably high impedance on your target input/load as you need to keep the Rs adequately high to keep from draining the battery.

If you wanted to get +/-12V from a 12V battery, or needed a lower impedance source, a couple of op-amps could be worked up into an equivalent circuit. E.g. two unit-followers, one inverting and one non-inverting, both fed, in counter-point, from the fixed divider and the variable divider, 0V from one output, signal from the other output.