A silly question but am little confused as to which one to go with. I would really appreciate if somebody could advise/comment on the schematic. With the best of my knowledge and google i guess my schematic would work. I don't have the parts to test this out but before i do i just need some advise. I have a project where i need to sample the mains voltage into my MUC (an Arduino) so i came up with this schematic of a precision rectifier, attached as CS. Explanation Idea here is to detect when the secondary of the Transformer (MOT) is shorted. The LIVE LOAD here is a transformer (MOT) used for Spot welding, when shorted i can a voltage drop from 1.0vac to 0.5vac i just need to send this voltage to the ADC of an Arduino. So here for isolation i used a MOC3052 from kynix. The LT1078 is a dual opamp precision rectifier from LT. C24 is a decoupling cap and C25 is to smooth the ac signal from LT. Then the second opamp is a buffer. Working The the optocoupler would be triggered by the MUC via 220? resistor there by shoring the contact from the LIVE_LOAD to the voltage divider and that goes on to send a dc voltage to the MUC. This happens when the MOT is not powered. When the secondary is shorted, there would be a voltage drop at the primary contacts of the MOT and that would also be seen by the LT1078 and using code, the voltage drop would be sensed by the MUC then the the optocoupler would be disabled and the MOT would be powered for spot welding. Basically an Auto Sense, instead of having to press a button to switch ON the MOT. Then i noticed this schematic from TI, attached datasheet page 4 Fig3 where a similar approach with less components. My basic requirement is to sense the voltage drop at the primary of the MOT and switch ON the MOT. Would really appreciate if anybody could advise.