This repo contins schematics and code to build a low cost ISM radio to wifi gateway.
Look at hardware/v4 for the hardware and verification for the software used to do hardware verification. The directory mqtt_sniffer contains an ISM to MQTT sniffer. Blog post is here.
git clone https://github.com/kanflo/espism.git
cd espism
git submodule init && git submodule update
cd mqtt_sniffer
vi esp-open-rtos/include/private_ssid_config.h # Fix wifi credentials
make && make flash
Wifi credentials, in case you did not know, are written to esp-open-rtos/include/private_ssid_config.h as
#define WIFI_SSID "your ssid"
#define WIFI_PASS "your key"