lowvoltage ac voltmeter

The main component of this circuit is an operational amplifier (such as the 741 or 351), configured as an amplifier whose feedback circuit is a diode bridge full-wave rectifier. An ammeter is attached to the rectifier circuit as shown in Figure 1 so that the op amp`s output current in both the positive and negative cycles flows through it in only

one direction. In effect, the average of the op amp`s output ac current io, which passes through the ammeter as a dc current, is measured by the ammeter. With full wave rectification, the meter current is given by: io = 0. 9 Vin/R, or Vin = 1. 1 ioR. Note that this project requires calibration so that the meter will register the rms value of the input voltage Vin.

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