# when given voltage, reverse voltage according to scale [closed]

I am given a DC line with a variable voltage along a set scale: let's say 0-10V. I would like to send an output DC line with a voltage reversed along that scale.
For example:

• 10 Volts in becomes 0 Volts out,
• 9 Volts in becomes 1 Volt out,
• 5 Volts in becomes 5 Volts out,
• 0 Volts in becomes 10 Volts out.

Note that the polarity is not reversed.

My question is: is there device I can buy or a relatively simple wiring scheme that can get me there? My intention is to take a signal from a PID tension-controller that controls a brake, and instead power a motor when needed. Oof, good question on the current. Let's say it is one amp.

## closed as too broad by Bimpelrekkie, Wesley Lee, Brian Carlton, laptop2d, PeterJSep 22 '17 at 9:44

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• 1) If you want an answer, ask a question. 2) Need more context; What exactly are you trying to achieve, and what for? – Dampmaskin Sep 21 '17 at 14:37
• Also mention how much current is needed. 0-10V is a standard control voltage for LED dimmers so are we talking about that? – peufeu Sep 21 '17 at 14:42
• I guess OP wants us to design a circuit for that. That's not what we do here. You can propose a circuit and we can comment on that and suggest improvements. But since you have no experience with electronics all I can tell you is: forget this. If this needs to be done get someone with experience in electronics. There are simply hundreds of things you would need to know even if we gave you a circuit design. – Bimpelrekkie Sep 21 '17 at 14:42

If you need the voltage just for indication or measurement then a simple DC differential amplifier with unity gain will do the job, because the output voltage is 10V minus input voltage: $V_{out} = 10V - V_{in}$. :

simulate this circuit – Schematic created using CircuitLab

Note that this circuit is not easy to build as it looks even for an experienced person because of the need of a negative supply (-12V). Also, generating the reference voltage ("10V" to the left-side leg on R2) can be problematic (e.g. voltage divider or from an outer generator).

• Hi Rohat! Thanks for the answer! I'm having difficulty running the simulation for that circuit, but it if it as described, I think we can do it. – RexPrestige Sep 21 '17 at 15:12