I used an LCD screen that's widely available for the very popular nokia low-end phones like Nokia 101, Nokia C1-00, X1-00 and similar because it's very cheap ( about $1.5 in the phones repair shops in my country, Iraq) and it needs only 4 GPIO's to drive and the most important thing is that it doesn't need any connector and can be soldered directly to the pcb. the same principle applied to the current measurement except that I use a current transformer here (75/0.1 A) and a shunt resistor (100 ohm) across the CT terminals to convert the current into AC voltage then measure it using the same way described in voltage. the basic idea of measuring AC voltage is to downsize the AC waveform using a resistor ladder, then DC-filtered and finally DC-biased to eliminate the negative part of the waveform by adding a dc voltage then enters to one of the ADC channels. The circuit is very simple that uses an STM32F030F4P6 Microcontroller, LCD, ESP8266 and a few SMD resistors and capacitors. And this is one of my humble projects that i would like to share. As an electrical engineer, I enjoy monitoring all electricity variables, locally and remotely.
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