Cave Pearl's Arduino-Powered Data Logger Cuts a Few Components for a Year-Long Battery Life
The Cave Pearl Project, an effort to map and understand the flow of water through cave systems, has unveiled a new variant of its data logging probe — and claims it can run for around two years on a single coin-cell battery.
"We’ve continued development of a 'lite' version of our [environmental data] logger with the lowest possible prep," project co-founder Edward Mallon writes. "That new baby is now ready for release with data download & control managed through the [Arduino] IDE's serial monitor window."
The new "lite" data logger is based around an Arduino Pro Mini board, connected to a real-time clock module. In an effort to reduce assembly time, lower cost, and limit power usage the original logger's SD Card slot is removed in favor of logging to EEPROM — adding complexity to the code, Mallon admits, but for a fair trade-off.
Dropping the power draw, though, required some modification. The real-time clock module has several components cut or desoldered to lower its power requirements — a hack which, Mallon admits, causes reverse current flow that the battery manufacturer warns could cause overheating and potential explosion. "The ones I’ve used so far survive the abuse without issue," he notes.
The Arduino Pro Mini, running at 8MHz, goes under the knife too: The reset switch is removed to prevent it being pressed when the assembly is put together in heat-shrink for stability, a regulator is clipped, along with the resistor connected to the power LED.
"This two module combination usually sleeps around 1µA and most of that is the RTC’s (IBATT) timekeeping current," Mallon explains, "as the [ATmega]328P should only draw ~150nA in powerdown mode. A […] realistic estimate would start with the assumption that the batteries only deliver about 110mAh with our logger consuming whatever we measured + 3µA (RTC actual) + 0.3µA (self-discharge).
"To be extremely conservative we can round that up to 5µA continuous, with four 5mA*10millisecond sensor readings per hour, and we still get an estimated lifespan of about two years."
More details on the effort to reduce power draw and hardware complexity are available on the Cave Pearl blog, while the source code has been published to GitHub.