UPDATE (2/22/2024): Jake Wachlin's Nanosleeper is now available to buy, offering a Feather-like form factor and a deep sleep mode that draws less than 100nA at 1.8V.
"[Powered] from a standard 220mAh CR2032 coin cell battery, Nanosleeper at <100nA could operate in its low power mode for more than 250 years," Wachlin writes of the finished board. "Of course, the battery won't last that long by itself, but Nanosleeper enables effectively free sleep for your project."
The Nanosleeper, which is built around an STMicro STM32L412, can be purchased on Wachlin's Tindie store now at $39; Wachlin has also designed a companion device, the MetaShunt, which offers high-range current measurement from 50nA to 500mA.
Original article continues below.
Maker Jake Wachlin has put together a development board built to deliver on a single goal: drawing under 100nA in power while in its deepest sleep mode, yet still allowing for wake-up from an onboard real-time clock (RTC): the Nanosleeper.
"Nanosleeper [is] a 'Feather-ish' development board achieving <100nA deep sleep current with real-time clock wake-up," Wachlin writes of his creation. "Leveraging the [STMicro] STM32L412 (capable of 18nA in Shutdown mode with pin wakeup), the [Micro Crystal] RV-3028-C7 RTC (capable of 1ppm timekeeping at 45nA with interrupt output), and the [Texas Instruments] TPS7A02 voltage regulator (25nA quiescent current), the Nanosleeper is a 1.8V Feather-sized (but not fully pin or voltage compatible) development board for ultra-low power applications."
The board was designed, Wachlin explains, to deliver an answer to one simple question: is it possible to build a functional development board that can sleep while drawing under <100nA at 1.8V yet wake on demand? "Ultra-low power systems can commonly achieve <10uA in deep sleep," he says. "Getting this down to <1uA is possible, but difficult (even good, modern ultra-low power microcontrollers, RTCs, and voltage regulators can require about 1uA to operate). Nanosleeper takes things another order of magnitude, down to <100nA at 1.8V. At <100nA, Nanosleeper would take >256 years to drain a CR2032 coin cell battery."
The heart of the board is STMicro's STM32L412 microcontroller, which runs at 1.8V — resulting in the loss of USB connectivity, Wachlin explains, with the board's USB Type-C connector used for power only. The board can also be driven from a battery connected to the TI TPS7A02 voltage regulator, up to a 6V input voltage. As a final power-saving feature, the design also incorporates a TI TPS22917DBV switched power output — meaning external hardware running from the Nanosleeper can be powered down completely while the microcontroller sleeps.
Tested in hardware, the Nanosleeper delivers an answer: while running a pair of LEDs the device draws 800µA as measured from a 3.3V battery connected to the regulator, dropping to 600µA when the LEDs are off but the microcontroller is in a busy-wait loop at 4MHz; when the device enters deep sleep, though, the power draw measured at under 95nA. "In summary," Wachlin writes, "IT WORKS! Nanosleeper achieves a deep sleep with timed wake-up at up to 4,095 minute periods while consuming <95nA!"