Cactus

🌵 Indoor WiFi-connected temperature and humidity sensor 🍶

power LiPO
wireless WiFi
sensor Humidity
mcu ESP8266
battery life 1 month
bom items 36
bom cost USD $26.92
vendors 5
completed May 2019

Lessons learnt

Good practices to continue for future projects

  • Buy electronics modules for V1.0 Make it work, make it right, make it better
  • Ensure main BOM components are available from vendors before schematic or layout
  • Check pin, pitch, manufacturer part number, function before buying BOM parts
  • Do a power tree analysis starting with power source before the schematic design
  • Test out paper mockups for mechanical dimensions
  • Do a mechanical consideration before laying out the footprint
  • Design a power on/off switch to start/stop using the battery
  • Leave out the module's on-board LED as a possible separate indicator E.g. Not linking GPIO02 to EN for the shift register
  • Don't use main chip's power output to enable other components, use another GPIO pin. E.g. Not linking 5V on WeMos to Vin of a sensor or shift register
  • Ensure the mechanical housing has an opening above any environmental sensors E.g humidity, UV index, air pressure
  • Make 2 units, not just 1 especially for non-interactive projects - one for deployment, one for iteration/testing
  • Tag the repository with the version number when the PCB is sent out for manufacturing

V2.0

For next iteration

  • No more modules
  • Reduce total BOM components
  • Do not use ESP8266's LED GPIO pin
  • Do not use ESP8266's 5V pin to power other components
  • Increase battery life by cutting off power to the sensors during sleep
  • Device an easy way to erase on board WiFi credentials and cloud connectivity details without the need to flash and re-flash the erasing firmware E.g. press a button
  • Tag the repository with the version number when the PCB is sent out for manufacturing
  • Make the measurement interval configurable without re-flashing the firmware

Similar projects

  1. Shelly H&T is a Battery Powered ESP8266 WiFi Temperature & Humidity Sensor

ESP8266

  1. ESP12-E pinout
  2. WeMos D1 mini 2015 schematic
  3. WeMos D1 mini pinout

Sensor Si7021

  1. Si7021 Adafruit Breakout board schematic
  2. Si7021 SiLabs datasheet
  3. Adafruit Si7021 Temperature & Humidity Sensor Breakout Board
  4. Arduino library for Si7020 and Si7021 environmental sensors
  5. MINI Si7021 Temperature and Humidity Sensor
  6. ESP8266 and Si7021 temperature sensor example

Shift register SN74HC595

  1. SN74HC595 TI datasheet
  2. 74HC595 pinout

Coin cell

  1. Shelly H&T is a Battery Powered ESP8266 WiFi Temperature & Humidity Sensor
  2. ESP8266 Sensor runs 17 days on a coin cell
  3. How to build an open WiFi finder using ESP8266 and two coin batteries
  4. How to Run Your ESP8266 for Years on a Battery

Battery shield

  1. WeMos battery shield
  2. Power usage of WeMos and battery shield
  3. Battery shield docs and schematic
  4. WeMos lithium battery shield
  5. Monitoring LiPo battery voltage with Wemos D1 minibattery shield and Thingspeak

Programming

  1. ESP8266 pogo jig programming

Design tools

  1. Creating an FPGA Power Tree
  2. System-Level Design Tool Quick Start Guide

Low power

  1. ESP8266 Low Power Solutions
  2. ESP8266 Maximum deep sleep i ~71 minutes
  3. Extend ESP8266 12 F Deep Sleep Time

Schedule

The Gantt Chart below indicates the actual time taken to complete this project. It can be used as a rough guidline when duplicating or iterating similar projects in the future.