The Sweech Aims to Bring Zero-Draw Standby Functionality, Alarm Wakeup to Almost Any Circuit

Yusuf Taiwo Hassan is aiming to bring low-power, timer-based standby to almost any hardware project, through an open source programmable switch dubbed the Sweech.

"Ever wanted to make your system come on at specific time in the day, perform a task and switch itself off? This is often hard to achieve with great power saving," Hassan writes of the inspiration behind the project. "Sweech is a programmable soft switch that handles that. It runs on a coin cell and switches on a much larger system at specific preprogrammed time of the day, week or year. This confers upon the whole system efficient and extraordinary power-saving since no device is on during the downtime."

The compact Sweech is a relatively simple design: At its heart is a Maxim Integrated DS3231 crystal-based real-time clock (RTC), which can be programmed over I2C. The RTC is linked to a soft switch, which is used to toggle power to an external circuit, while power to the Sweech itself comes from a single coin-cell battery in an internal holder.

"The concept of the system is as simple as it seems," says Hassan. "The INT pin of the DS3231 is open drain and is pulled up externally to the battery input (labelled VCCQ). The RTC chip pulls down the pin during an alarm and will remain low until the Alarm bit is cleared by the host MCU by I2C. The gate of PFET Q2 is connected to the pin to ensure that it is controlled by the Alarm."

Hassan is currently finalising the design of the Sweech, including the potential for a higher-end variant with on-board rechargeable battery; more information can be found on the project page or in Hassan's GitHub repository.