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
Would this be what you're looking for?
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.
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