The op-amp rectifier in Fig 1 operates from a single supply and provides a logic output and an LED that indicate the state of the input voltage. The input-state indications are handy for calibration.
The op-amp rectifier in Fig 1 operates from a single supply and provides a logic output and an LED that indicate the state of the input voltage. The input-state indications are handy for calibration.
Because the circuit operates from a single supply, the 2.5V reference determines the level around which the circuit rectifies input waveforms.
In operation, if the input is above the 2.5V reference level, IC2D acts as a follower. Therefore, the inputs to R1 and IC2B's noninverting input track the input. IC2B's output also tracks the input signal. The output of IC2A, acting as a comparator, goes to 0V.
If the input goes below the 2.5V reference level, IC2A's output goes positive, clamping its inverting input to the 2.5V reference (plus or minus the input offset). IC2B now becomes a gain-of-1 inverter. IC2A lights the LED and, with the help of D1 and D2, provides a high logic-level output. If you need a higher output logic level, add another diode to the D1/D2 string or change D2 to a low-value Zener diode. (DI #1561)