Prometheus Temperature Sensor

A WiFi enabled temperature and humidity sensor built around an ESP8266 module with a Prometheus metrics endpoint.

Hardware

The PCB is designed to be made with entirely through hole components to make DIY assembly easy without having to mess around with fiddly SMD components.

Design

MCU

The ESP-01 module has been used to control the sensor. This is a small module based upon the ESP8266.

Temperature / Humidity Sensor

The temperature / humidity sensor that we have used for this design is the AHT10 although any sensor that works with 3.3V and uses I2C could probably be made to work.

Power

You can power the board in 3 different ways. There is a DC jack, a USB connector (this also doubles as a serial interface for configuration) and finally a JST battery connector to allow make the sensor portable. All power inputs support from 4-12V DC. Power is regulated using a MCP1702 low dropout regulator to minimize the voltage drop from power input to the board power supply. Each input has a 1n5817 diode on the positive input to prevent reverse powering of devices. This does also induce a slight voltage drop so you may require a power supply slightly above 4V, perhaps 4.5V.

Design Software

The schematic and board design were both drawn using KiCad, an open source electronic design automation suite.

Firmware

Build Environment

Toolchain and SDK

You will need to setup both the toolchain for the ESP8266 as well as the ESP8266 RTOS SDK. Espressif provide documentation for the setup of both components.

• Toolchain Setup
• SDK Setup

Environment Variables

Two environment variables are used to tell esptool.py (the tool used by the SDK to flash your firmware to the ESP8266) where to flash to and at what speed.

• ESPPORT - This is the path to the device to program, e.g. /dev/ttyUSB0.
• ESPBAUD - Baud rate to communicate at. Should normally be set to 115200 for flashing.

If you encounter an error such as below when running make flash you probably need to set the ESPPORT environment variable.

A fatal error occurred: Cannot find target port named 'None'.
CMake Error at run_esptool.cmake:45 (message):
  esptool.py failed

Other requirements

You will also need CMake and Make installed to compile and flash the firmware.

Build and flash

Initialize build system

First create a build directory in src and cd into it.

mkdir build
cd build

Then you can run CMake to generate the build system.

cmake ../src

Compile and upload

To compile the firmware run:

make

And to upload to the board run:

make flash

make flash will also compile the firmware before it uploads it to the board, so you can omit running make separately if you like.

Licence

This repo uses the REUSE standard in order to communicate the correct licence for the file. For those unfamiliar with the standard the licence for each file can be found in one of three places. The licence will either be in a comment block at the top of the file, in a .license file with the same name as the file, or in the dep5 file located in the .reuse directory. If you are unsure of the licencing terms please contact mnickson@sidingsmedia.com. All files committed to this repo must contain valid licencing information or the pull request can not be accepted.