# Controlling Voltage Range from Sensor Signal

I have a project where I would like to control a range of voltage outputs from a sensor signal. In this case, taking a signal that is 0-10 volts, and using some method to only allow the range of 4-6 volts to "pass" through. All voltages below 4 and above 6 would read as 0. Or in another case, for example, only allow voltages from -1 to 1 volts to "pass" through, while voltages -10 to -1 and 1 to 10 read as 0.

On top of that it would be beneficial to be able to lower that range by using some type of voltage divider with a potentiometer, for example, making the range 4.5 to 5.5 volts.

The goal is to have an adjustable deadband. Normally when the sensor reads 5V, there is no actuation. I want to make it so I can control the no actuation range, i.e. from 4-6 volts there is no actuation. I want to do this with just analog circuitry.

I have thought of zener diodes and tried different op-amp scenarios but have not discovered anything yet.

Any ideas? Snippet of relevant circuit.

The left most opamps compare the voltage of a sine wave generator (in your case the output of the sensor, Vsensor) to a given threshold. The thresholds are set with two potentiometers. As long as Vsensor is between these two threshold voltages the outputs of the opamps cancel each other out and the mosfets won't conduct.

As soon as Vsensor goes above your desired range the positive voltage from both opamps will enable the left most mosfet causing the voltage to drop across the resistor which will make your output 0v.

If Vsensor drops below your desired range both opamps will output a negative voltage and the opamp on the right hand bottom will invert the signal to a positive one which will cause the right most mosfet to conduct which will drop the output voltage to zero.

I think the right most N-mosfet together with the inverting opamp can actually be replaced with a P-mosfet but I am not proficient enough to tell you how, perhaps someone in the comments can shed a light?

I used http://www.falstad.com/circuit/ to simulate this circuit, and this is the specific circuit: circuit.

Good luck!

Edit:

A pass or stop filter can be achieved by adding a differential opamp that subtracts Vsensor from Vfilter and an inverting opamp that corrects the sign of the voltage. circuit

• Thanks for the schematic! It does work, how would I change it up to do the opposite. To allow voltages from 0-4 to and 6-10 to pass through, while stopping voltages between 4 and 6? Commented Nov 27, 2017 at 1:30
• I changed the schematic so you can now alternate between pass and stop. You may want to try and breadboard this and maybe play around with the resistance values; I don't know the source impedance so it could still be pulling too much current. Also pay attentions to the matched resistors; any difference between them is going to scale / multiply your output voltage. Commented Nov 27, 2017 at 15:36