Single supply opamp circuit with a bidirectional signal

[Styx]

I'm am scratching my head to see if it is possible to use single-rail OPAMPS (so I don't have to create dual-rails) in a project I am looking into

There is a time-varying signal between +10V and -10V. It cannot be treated as an AC signal since the signal could dwell at a level for a significant period of time(ie cannot high-pass + DCoffset)

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Its basically a speed demand that I can receive from a box of tricks.


Now I want to generate a signal that is HIGH when it is >0V and LOW when it is <0V.
Likewise I want a signal that is just the absolute of this time-varying singal

Simple enough with a dual-supply: comparator cct to produce a HIGH/LOW based upon the sign of the signal and a precision rectifier BUT is it possible todo with single-supplies? I have been sketching and simulating different methods to basically pot it down and offset it by a a bit (say x0.5 + 5 to make it a 0->10V signal on 5V) but it doesn't seem possible.

or am I wrong?

 

[MrAl]

Hi,

You should be able to offset the input signal to get it into the range of 0 to +10 or whatever you want.

For a very very simple example, connect two equal resistors between +10v and ground, say 2k each. That puts +5v at the center of the two resistors. Now using a third higher value resistor like 10k, connect that to the center of the two resistors and connect the other end of the 10k resistor to the input signal. Now when the input signal goes to +10v you get a voltage at the junction of all three resistors of something like 6v, and when the input goes to -10v you get a voltage at the junction of something like 4v. All you have to do then is detect either something like 4.5v or 5.5v to figure out if the signal is high or low.
If the signal varies more then we'd want to increase the junction range. Decreasing the value of the 10k resistor would give us a higher range. We could probably get it up to 0 to +10 for an input of -10 to +10 volts, but this is just a quick example.

 

[dr pepper]

You can buy industrial gizmo's to do this.
A precision rectifier does the job, and you'd need a comparator for the sign, you can use a resistor divider to reduce the i/p swing.

 

[crutschow]

**broken link removed** a single supply full-wave precision rectifier circuit that requires no diodes.