David Capper's Soil Moisture Monitors Tap Ynvisible's ePaper Displays to Get Years-Long Battery Life
A single coin cell can run one of these self-contained soil moisture monitors for nearly two and a half years, their creator claims.
Lead engineer David Capper has designed a self-contained soil moisture monitor for those whose green thumb needs a little help — leaning on an energy-efficient ePaper display to provide information at a glance.
"I’ve always been a bit rubbish at looking after plants," Capper admits. "I'm not a particularly organised person and all too often I forget to water them so they end up being in a near permanent state of drought. Thinking about it, the core problem I was trying to solve wasn't watering the plants, it was knowing when to do it. If I have an indicator that lets me know when the soil is getting dry then I don't mind having to use a watering can myself."
Having had such a device in the back of his mind for a while, Capper's maker instinct was finally triggered after happening across an ultra-low-power display from Ynvisible: an electrochromic ePaper panel that shows a seven-segment bar graph but, unlike a traditional LED or LCD bar graph, only requires power when changing states and retains its last state even when power is completely removed.
"I really love the idea of low power projects with a long life — especially when there's the prospect of them running for years on a simple coin cell," Capper says. "I bought some samples and fired up KiCad ready to start designing."
Capper's board design pairs an Ynvisible bar graph display with an STMicroelectronics STM32l010F4 — "at the time of design," he explains, "this was the cheapest, lowest-power offering I could find in STM[icro]'s line-up," and a coin cell battery for power. The bottom of the board is built as a capacitive moisture sensor, designed to be inserted into a plant's pot and measure how moist its soil is — reporting the result on the ePaper display, while drawing such little power Capper estimates it should run for nearly two and a half years per battery change.
More details on the project are available on Capper's website, while he has put some assembled boards up for sale on Hortus.dev at £22.50 (around $29).