This circuit is the current sense amplifier setup used on the cheapest 3 digit volt/current panel meters from China. I have added a separate voltage source with light bulb/switch to simulate a load on the current shunt. I also added a voltmeter and 500k resistor on the op amp output to simulate the input to the microcontroller.
The actual device:
I do not have a DMM with the resolution needed to measure the current shunt directly and I've been too lazy to set up a precision current source to figure it out the other way. So I can't say exactly how much the amplification factor is. The shunt appears to be around 10 to 20 milliohms.
I sourced this circuit from tearing apart one of the cheap $2 digital voltmeters. I retraced the board, measured all capacitors, and created a video on YT showing my work for the entire PCB (link below). The video is not monotized. I look at it as a simple community resource that I want to share. The video has no vocals and has a title/basic description translated (poorly using Google Translate) into 12 languages. I didn't find a full schematic or datasheet for the device, so I created a couple of schematics on KiCAD and uploaded them to my GitHub page. The KiCAD .pro files are also on GitHub along with the library folder for schematic components I made so anyone familiar with KiCad can use or modify the schematic however they want.
My overall goal is to enable me to play around with the ST microcontroller (STM8S103F3P6) used on this device... eventually. While retracing the board I've documented the programming port and connections.
LINKS
YouTube Video
https://youtu.be/UubXv_w4x5s
GitHub Repository
https://github.com/Upcycle-Electronics/DSN-VC288
GitHub Schematic version 2 PDF
https://github.com/Upcycle-Electronics/DSN-VC288/blob/master/PDF's/V2.0 DSN-VC288.pdf
[ Note if your on a mobile device like me and unfamiliar with GitHub, be sure to use the 'request desktop version' in your browser options when using Git.]
-Jake
