RelayMCU

For more details: https://cmheong.blogspot.com/2020/01/hacking-hw-655-esp8266-wifi-iot-relay.html

Code for STC15F104W MCU which was installed in cheap ESP-01 relay module marked "LCTECH".

I bought few such modules from ebay but they had broken MCU firmware and not works. It must accept on UART commands (hex): A0 01 01 A2 for Relay ON and A0 01 00 A1 for Relay OFF

UART interaction code I got from STC15F100 docs http://www.stcmicro.com/datasheet/STC15F100-en.pdf

By the way this MCU has very similar architecture to 8051 MCU so some code which works on 8051 MCU also may work there.

To compile this code under linux run:

sdcc -mmcs51 --iram-size 128 --xram-size 0 --code-size 4096 --nooverlay --noinduction --verbose --debug -V --std-sdcc89 --model-small "relay.c"

To upload code into MCU connect module to USB UART as shown on picture run this

stcgal -p /dev/ttyUSB1 -b 1200 -D -t 11059 relay.ihx

disconnect +5V (red wire on image) and connect it again for start flashing.

Modification ONE.

Relay board MCU is connected to relay by pin 3.2. This pin has high level on cold reset or power on so device based on this board will click each boot time. To avoid this issue I added 2K resistor between pin 7 of MCU and GND and changed code by configuring push-pull mode on P3.2ch MCU pin 3.2. See article "How to Make I/O Port Low after MCU Reset" in STC15F100 docs.