You need to design a circuit that senses when a signal is greater than some reference threshold voltage. When the signal is greater than the threshold you want to generate a positive constant voltage (say +10 Vdc) and when the signal is below the threshold you want to generate 0 Vdc. One way to do this is with an op-amp used as a comparator, i. e., the noninverting and inverting inputs are "compared" and the output swings such that it tries to make them equal but there is no feedback so the output just swings all the way to the + and - Vcc used to power the op-amp. Let’s take it by the functional parts:
(a) You don’t have the luxury of DC power supplies to establish the threshold voltage or to power the op-amp but you do have a 120 Vac to 24 Vac step-down transformer. You also have access to diodes, capacitors, and resistors.
Design a circuit to deliver +10Vdc to power the op-amps and +5Vdc to serve as the threshold voltage value to compare the signal to. The individual outputs shouldn’t droop more than 10% when loaded by 10k.
(b) Comparator: Design the op-amp "comparator" circuit that accepts the signal as one input and the threshold voltage (created in part (a) above) as the other. Don’t forget the op-amp +/- power inputs (also created in part (a) above)! What values should these be, i. e., what should be connected to them from the circuit elements you have already designed (remember you don’t have DC power supplies)? Sketch the expected output of the comparator circuit against some arbitrary input waveform that oscillates above and below the threshold voltage.