ESP8266 interfacing

When is required to connect many ESP8266 devices together SoftwareBitBang strategy is extremely handy. In the picture below it is shown how 2 or more ESP8266 can be connnected to a common ground and a common wire used for communication.

Before creating a mixed 3.3v-5v bus be sure devices are 5v tolerant. When connecting an Arduino UNOs to an ESP32, consider that voltage level converters available in the market are often not compatible with PJDL, you can try this alternative approach proposed by alastaira instead. It isn't truly converting voltage levels but it is much quicker and cheaper than designs based on transistors.

Consider seriously the risks involved in connecting an ESP8266 to a wired SoftwareBitBang bus, all connected devices may be potentially compromised, manipulated and remotely actuated against your will. It should be a good practice not to connect to the internet systems that may create a damage (fire, flooding, data-leak) if hacked. If the internet connection is not required in your project but you are still using an ESP8266 consider to connect the antenna pin with ground to exclude any possible vulnerability exposed by the WiFi.