# 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.

• 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: $V_{out} = 10V - V_{in}$. :