I posted this on the microchip forum too, but did not get any answers.
I need to design a low cost AC Over current switch based on PIC16F676. It reads the line voltage (Half Cycle Resistor Divider) and the Current (0.1 Ohms Shunt Resistor). The max load being 4 amps AC/240V
I am using a capacitive power supply due to cost factor. To keep things simple I am using a single 5.1V supply derived from it.
Now my problem is a single supply AC voltage amplifier. The voltage derived from the shunt needs to be amplified and rectified to be read by the ADC. I tried with a LM358 with the non-inverting input biased to 1/2 of the supply voltage followed by a precision rectifier. It did not work as intended. Non-linear response.
Any pointers on the analogue interfacing part ?? That is amplify+rectify voltage derived from the shunt