Witty Pi is an add-on board that adds realtime clock and power management to your Raspberry Pi. It can define your Raspberry Pi’s ON/OFF sequence, and significantly reduce the energy usage. Witty Pi 4 is the fourth generation of Witty Pi and it has these hardware resources onboard:

Factory calibrated and temperature compensated realtime clock with ±2 ppm accuracy.
Dedicated temperature sensor with 0.125 °C resolution.
On-board DC/DC converter that accepts up to 30 V DC.
AVR 8-bit microcontroller (MCU) with 8 KB programmable flash.

Accurate realtime clock and ON/OFF scheduling

The realtime clock (RTC) on Witty Pi 4 has been calibrated in the factory and Witty Pi 4’s firmware also makes temperature compensation for the crystal. This makes the RTC very accurate and the actual annual error is limited within ±2 ppm. When your Raspberry Pi boots up, the time stored in the RTC will overwrite the system time. As a result, your Raspberry Pi knows the correct time even without accessing the Internet. You can schedule the startup and/or shutdown of your Raspberry Pi, and make it a time-controlled device. You can even define a schedule script to schedule complicated ON/OFF sequence for your Raspberry Pi.

Scheduling the ON/OFF sequence for Raspberry Pi is the most popular feature of Witty Pi, and it is extremely useful for systems that powered by battery. By only turning on Raspberry Pi when necessary, the battery can be used way much longer with Witty Pi installed.

Temperature-controlled device

The temperature sensor on Witty Pi 4 has 0.125 °C resolution. The temperature data is used for compensating the crystal and make the RTC more accurate.

You can also specific the action (startup or shutdown) when temperature goes above or below the preset threshold. Which means you can also make your Raspberry Pi a temperature-controlled device.

DC/DC converter and e-latching power switch

Witty Pi 4 comes with a DC/DC converter on board, which allows you to power your device with 6~30V power supply. You can also power your device with 5 V via the USB type C connector.

Witty Pi 4 also implements an e-Latching power switch, which is very similar to the power switch on your PC/Laptop computer. You can gracefully turn on/off your Raspberry Pi with a single tap on the button. The software running in background will execute the shutdown command before the power gets cut, this avoid the data corruption caused by hard shutdown.

Witty Pi 4 supports all Raspberry Pi models that has the 40-pin GPIO header, including A+, B+, 2B, Zero, Zero W, Zero 2 W, 3B, 3B+, 3A+ and 4B. You will need to solder the 40-pin header to Zero/Zero W/Zero 2 W model beforehand, so they can make reliable connection with Witty Pi.

Single I²C device

Witty Pi 4 uses MCU to emulate a single I²C device with default address 0x08, and also map all I²C registers in realtime clock and temperature sensor as virtual I²C registers in the same device. You can access all I²C registers in realtime clock and temperature sensor via the single I²C device emulated by Witty Pi 4.

The advantage of this new design is that Witty Pi 4 hides other I²C devices (realtime clock, temperature sensor) and becomes the proxy of them to talk to Raspberry Pi. Because the I²C address used by Witty Pi 4 can be changed to any value, you can always avoid the I²C address conflicting.

UWI support

Witty Pi 4 is fully supported by UWI (UUGear Web Interface), and you can access you Witty Pi 4 on any device that have network access.

Specifications

Microcontroller	ATtiny841 (datasheet)
Realtime Clock	PCF85063A (datasheet), calibrated in factory
Temperature Sensor	LM75B (datasheet)
DC/DC Converter	MP4462 (datasheet)
MOSFET Switch	AO4616 (datasheet)
Battery	CR2032 (for time keeping when power supply is disconnected)
Power In	DC 5 V (via USB type C connector) or DC 6 V~30 V (via XH2.54 connector)
Output Current	Up to 3 A for Raspberry Pi and its peripherals
Standby Current	~0.5 mA
Operating Environment	Temperature -30°C~80°C (-22°F~176°F) Humidity 0~80% RH, no condensing, no corrosive gas
Dimension	65 x 56 x 19 mm
Weight	23 g (without accessories)

Included

1x Witty Pi 4 board
1x CR2032 battery
4x M2.5 x 11mm Copper Standoff
8x M2.5 screws

Details