A WiFi-Enabled Red Lion T48 Temperature Controller via the ESP8266

This post is still a work-in-progress.

To enhance control and monitoring of the pool heater (boiler) at Fairway Farms Swim Club, a project was kicked off in early 2020 to replace a Johnson Controls A419 temperature controller with a more visible, remote-accessible unit.

Like most projects at the club, this build utilizes high-quality components purchased at a discount via surplus. Where possible, off-the-shelf items are selected in lieu of custom solutions, especially for core functionality.

The temperature controller is based around a Red Lion T48 temperature controller (T4820219). This particular unit operates from 18 to 36 VDC and features logic/SSR outputs for the main control and Alarm 2 and an RS485 interface. NOTE: This particular unit has been discontinued by the manufacturer.

A DIN rail-mounted prototype board holds an NodeMCU (ESP8266) module, with a TI SN65HVD11 3.3 V RS-485 transceiver, some input interface circuitry and a CUI VXO7803-1000 DC-DC converter. An SSD1306 OLED display was added for enhanced network/communication diagnostics.

A Lambda DPP15-24 provides 120 VAC to 24 VDC conversion for the temperature controller and DC-DC converter on the prototype board.