Discussion in 'Electronic Design' started by [email protected], Sep 7, 2007.

1. ### Guest

Is there a way to build a two-way differential circuit i.e. a circuit
that compares a varying voltage to a reference, and if that voltage is
rising, it gives a certain value (say 1), while if its decreasing, it
gives 0. I was thinking of using a quad comparator but is there a
simpler solution? TIA

2. ### Guest

Would this be what you're looking for?
http://www.cgs.synth.net/modules/cgs62_sd.html

How about: Take a capacitor, connector one side to your signal (assumed to be
low impedance), the other side to a small resistor. Size the resistor and
capacitor such that the reactance is much greater than the resistance (in
general, this means a rather small R). The idea is that the circuit looks
like just a capacitor to the input, so I is still very near equal to C*dv/dt,
but you generate an output voltage across the resistor (Vres=C*dv/dt*R) which
is the derivative of the input signal. The sign of that voltage tells you is
the voltage is rising our falling -- use a single comparator to "square it up"
if you need to.

You'll probably also need a bit of filtering/hysteresis in the system so that
noise doesn't cause the output to oscillate wildly when the input signal is
stationary.

4. ### DleerGuest

you need a simple "window" comparator circuit, 2 comparators and some
resistors  