# Convert 0 - +5 volt input signal to -5 - 0 volt output.

#### LenoB

Joined Jun 22, 2018
4
I am using DAC1 on an Arduino Duo board to create a waveform that runs 20 hz and varies from 0 to 5 volts. I want to shift the output from 0 - +5 volts to -5 - 0 volts. Have tried several different op amp circuits and nothing is working for me. seems like it should be a fairly simple thing to do but the solution is eluding me.

#### crutschow

Joined Mar 14, 2008
30,122
Do you have a negative supply voltage for the op amp?
You need that obviously to get a negative output voltage, since op amps can't output a voltage greater than their supply voltages.

Just connect an inverting op amp circuit with a gain of -1 to a plus and minus supply of adequate voltages for your op amp.
That will give you the desired signal out.

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
And change the DAC code. I do believe there exists a +1, -1 gain selectable OP amp.

#### LenoB

Joined Jun 22, 2018
4
Do have Duel power supply.
The info for the Arduino DUO says "Please note that DAC output range is actually from 0.55 V to 2.75 V only.". So I am not going to get a 0-+5 volt output. So looking for a circuit that will convert the .55-2.75 volt signal to a -5 to 0 volt signal. I have Function generators that provides and offset adjustment that allows the user to adjust the output signal up or down without affecting the gain.

Joined Mar 10, 2018
4,057
Basically a summer with G is what you need.

Do you want .55 to 2.75 translated to 0 to -5 or
- 5 to 0 ? In other words as input to summer increases
do you want its output to go more negative or less ?

Look at summer and diff subtractor circuits -

https://www.ti.com/seclit/sl/slyy137/slyy137.pdf

If your supplys are +5 and -5 use RRIO opamp.
Otherwise use supplies that meet CM requirements
of opamp and design.

Regards, Dana.

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
Even with a +-5V supply, you can't reach 5 V. You can get pretty close though.

#### LenoB

Joined Jun 22, 2018
4
Input Signal starts at 2.75 volts and decays to .55 volts. Want the output to start at 0 volts and decay to -5 volts...

Joined Mar 10, 2018
4,057
Last edited: