Witty Pi 4 Mini: RTC and Power Management for Raspberry Pi

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 Mini is the fourth generation of Witty Pi and it has these hardware resources onboard:

• Factory calibrated and temperature compensated realtime clock with ±2ppm accuracy.
• Dedicated temperature sensor with 0.125 °C resolution.
• AVR 8-bit microcontroller (MCU) with 8 KB programmable flash.

Witty Pi 4 Mini has very similar design with Witty Pi 4, however it doesn’t come with a DC/DC converter onboard, and it uses super capacitor for RTC time keeping when no power supply is connected. Witty Pi 4 Mini has solder pads on the back, which allow you to solder a DC/DC converter (LDO or switching DC/DC converter) there.

ACCURATE REALTIME CLOCK AND ON/OFF SCHEDULING

The realtime clock (RTC) on Witty Pi 4 Mini has been calibrated in the factory and Witty Pi 4 Mini’s firmware also makes temperature compensation for the crystal. This makes the RTC very accurate and the actual annual error is limited within ±2ppm. 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 Mini 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.

E-LATCHING POWER SWITCH

Witty Pi 4 Mini 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, and it avoids the data corruption caused by “hard” shutdown.

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

SOFTWARE INSTALLATION:

Witty Pi 4 Mini uses the same software as Witty Pi 4. You just need to run these two commands in your Raspberry Pi to install Witty Pi 4 Mini’s software:

The software and firmware of Witty Pi 4 Mini are open-sourced. You can find the source code on GitHub.

PACKAGE CONTENT:

Each Witty Pi 4 Mini package contains:

• Witty Pi 4 Mini board x 1
• M2.5 x 10mm plastic screws x 4
• 4mm plastic spacer x 4
• M2.5 plastic nut x 4