Monomymous maker Marcel has designed a low-cost environmental monitoring gadget with a very specific purpose in mind: ensuring the comfort of pet beetles inside their habitats.
"Raising a beetle is fun and wholesome but keeping an eye on the environment inside the little fella's enclosure can be stressful and complicated," Marcel explains of his creation. "For this reason, the BeetleMeter is a tiny battery-powered PCB that instantly notifies the beetle keeper if the temperature and humidity is too high, too low or just right, by the push of a button."
The compact device, designed to be largely unobtrusive in the beetles' habitat, is built around a Microchip ATtiny402 microcontroller — a shift from an earlier, larger design which used the ATtiny85 — connected to a Sensirion SHT40 temperature and humidity sensor delivering a ±0.2°C temperature and °1.8% relative humidity accuracy.
"Due to the limited amount of GPIO [General-Purpose Input/Output] pins of these two microcontrollers," Marcel notes, "the LEDs are switched through Charlieplexing. V1.0 incorporates the button signal on one of the remaining GPIOs and in V2.0 the button is used to power the system.
"Both versions board outline is defined by the dimensions of their battery holder, which is mounted on the bottom side of the PCB. The top side accomodates the remaining components in SMD [Surface-Mount Device] format. The push button size was also chosen according to the board space left."
There's no wireless connectivity on the board, and in the latest revision it stays entirely powered down until and unless the button is pressed — at which point it wakes up and takes stock of its environment, providing a simple traffic-light-like approach with three LEDs each for temperature and humidity indicating a high, low, or good value.
Marcel has published the project to GitHub, with the hardware design files and source code available under an unspecified open source license; the maker estimates the hardware cost to be somewhere around the $2 mark per unit.