Cheap IoT technology to replace analog humidity and temperature loggers

I started my career in museums back in the early eighties and introduced some of the early collection management software systems. In those days environmental conditions in museums were monitored using analog data loggers. These were mechanical devices, featuring a humidity and temperature plotting system. Good stuff, they were driven by a “clock-work” that needed regular winding up. The “data” was drawn by little pens on rolls of paper.

( Classic analog data logger )
Today IoT, or Internet of things is the buzz word. As an experiment I decided to see how feasible, cheap or expensive, it is to create a similar system using state of the art microelectronics. My wish list:
  • Use standard components
  • Low-power (battery powered)
  • Wireless data connection (Bluetooth and/or WiFi)
  • Easy to program (using Arduino development tools)
  • On-system display

This led to the following prototype consisting of:

  • ESP/Vroom 32 microcontroller board (15-20 Euro)
  • A Siemens BME280 humidity/temperature/air pressure sensor (15-20 Euro)
  • A 4.3” e-paper display (50 Euro)
  • A bread board (5 Euro)
The total cost of the system is under 100 Euro, of course without a case. Obviously, the e-paper screen is the expensive part. If you do not need an on system display, then the whole system costs less than 50 Euro. One could also replace the e-paper display with a 2 lines LCD screen, but then you lose the graphical capability.
( Digital data logger with E-paper display )
( Digital data logger with standard LCD screen )
Features of this setup:
– Low power, the ESP32 has a deep sleep mode that puts the board in a state where it hardly draws any power. The E-paper display keeps its information and does only draw power when it is updated.
– Industrial graded sensor, from a renowned supplier, see
– Wireless connectivity, the ESP32 offers both WiFi and Bluetooth (BLE = low power version) connectivity. With these capabilities one could transfer environmental data directly into a collection management system. Multiple systems can be integrated in a single system.
In this setup I used the development board from the maker of the ESP32,

Alternative version

In my alternative version with a standard LCD display I used the same ESP32 on a development board from Sparkfun, the ESP32 thing. ( I like this board even more than the original development board, it is narrower, which leaves space on both sides of a bread board to connect wires. It also has a built in connector for a LiPo rechargeable battery pack plus an onboard charger. Just plug it in to a LiPo battery (approx.. 10 Euro) and a USB wire is capable to charge the whole system after which it can work for days without recharging (no, no more ticking and winding up).
Please contact us and let’s talk if you can imagine applications for your institution.

Bert Degenhart Drenth, DDigit – 08/03/2019