ESP8266 Thermocouple Transmitter With OTA Update

I just made a PCB to measure the temperature of a type K thermocouple and send the temperature to PLC via Modbus TCP.

Problem 1

The first problem I faced was power management and remote update/management of sensors. There will be more than 1000 sensors and there wasn't any simple way to control or upgrade them.

I tested many ideas on the internet about power management and all of them were just theory. The main point of ESP8266 power saving is the power supply voltage. The ESP8266 draws 20uA in sleep mode when it supplied with 2.5v and it normally with 3.3V which means you should have two modes of power supply, Sleep mode (2.5v) and operation mode (3.3v).

On the first line of the program, you should make the power supply to 3.3v mode and you have to change it to 2.5v after ESP8266 goes to sleep. I just used a P channel MOSFET in parallel with 2.5v linear regulator. When ESP starts, I turn on MOSFET and all battery voltage is on ESP. Don't worry about overvoltage it can't harm ESP (4.2v). The ESP measure and transmit temperature in 650ms and come back to sleep.

Problem 2

The second problem was managing and upgrading firmware. For any changes I should reprogram 1000 devices in separate places then takes about a month. I searched a lot on the web and I found a great OTA service named OTAdrive.

In OTA drive you can simply configure and upload firmware to the sever, devices will get new firmware and you can see their online status and versions. It let you grouping devices for each customer of the model. It was all I need.

As you see I installed my first version in a factory out of the city. I hope it works perfectly after 3 months of test cycle.

Hope to solve any problem to you