# Convert 0-5V from DAC into +/-5V?

I am trying to control a galvanometer that requires +/-5V input voltage, my source is a 14Bit DAC (LTC2612) that I control via an Arduino. I use a +/-15v powersupply to power the galvanometer.

What would be the best way to convert the output of the DAC to suite the input needs of the galvanometer? I have a LM358 dual op-amp if that is a way to go?

• What current does the galvo draw? Sep 27, 2015 at 0:29
• I am not sure actually, the spec states "Input voltage requirements: +15V/1.0A, -15V/0.6A" Sep 27, 2015 at 0:33
• Sep 27, 2015 at 0:34
• Does the galvonometer have a part number, datasheet. etc? Those figures you gave are for its power supply, not the signal input. Sep 27, 2015 at 0:37
• Ah, then I take it that the galvo has an amplifier built-in? Sep 27, 2015 at 0:40

Assuming the galvo amplifier has a relatively high impedance input (doesn't draw more than a few mA) you can use this circuit:-

simulate this circuit – Schematic created using CircuitLab

The amplifier has a gain of -2 from the DAC output, and D1/R2 biases the voltage at +5V out with 0V in, so the output will change from +5V with 0V in to -5V at 5V in. R4 provides some vias current for D1, which is the -5V reference to offset the amplifier.

If you want to avoid D1 and have a 5V reference already, you can use the remaining amplifier to get -5V from the +5V reference as shown in the dashed box.

• Thanks alot! I went with option 1 to be able to use both OAs for X and Y axis of the galvanometer. Sep 29, 2015 at 19:49

An opamp can do that and you will need to arrange your software to drive the DAC appropriately.

Here is a TI application note that applies to this. It has the equations to modify the resistor values for your particular applciation.

I assume that the galvonometer is sensitive enough to be driven directly from the opamp - it must take less than ~20mA at fullscale or the opamp will not be powerful enough.

Converting unipolar DAC to bipolar output

You should use the reference voltage that you supply to your DAC as a means for generating a proper bipolar output using an op-amp: -

This is the most accurate method of acheiving what you want. TI also show the same type of circuit: -

They describe their circuit as: "Bipolar +/-10V Output from a Unipolar DAC for Industrial Voltage Drivers" but this is an enhanced range due to the addition of RG1.