Witty Pi 4 Mini - RTC & Power Management for Raspberry Pi

Product ID: 5038


Witty Pi 4 Mini is an add-on board that adds real time clock (RTC) 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.

It's a small electronic board that can add real-time clock and power management to your Raspberry Pi. Witty Pi 4 Mini is a new member of the fourth generation of Witty Pi, and it has bonnet/pHAT form factor.

Please note, our demo photo shows it with a "2x20 Riser Header" which is NOT included!

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

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.

After installing Witty Pi 4 Mini on your Raspberry Pi, you get some amazing new features:

  • You can gracefully turn on/off Raspberry Pi with a single tap on the switch.
  • After shutdown, Raspberry Pi and all its USB peripherals’ power are fully cut.
  • Raspberry Pi knows the correct time, even without accessing the Internet.
  • Raspberry Pi knows the temperature thanks to the sensor in the RTC chip.
  • You can schedule the startup/shutdown of your Raspberry Pi.
  • You can even write a script to define a complex ON/OFF sequence.
  • Monitor external voltage and turn on/off your Raspberry Pi accordingly.

Witty Pi 4 Mini supports all Raspberry Pi models that have the 40-pin GPIO header, including A+, B+, 2B, Zero, Zero W, 3B, 3B+, 3A+, 4B, and Pi 5.

Raspberry Pi communicates with the RTC chip (PCF85063A), temperature sensor, and microcontroller on Witty Pi 4 Mini via I2C protocol. The microcontroller has an adjustable I2C address: 0x08 which 'shadows' the other I2C devices so you never have to worry about I2C address collisions.

There is a /WittyPi3/ version and a /WittyPi4/ version for download from the mfr. web page.. You just need to run these two commands in your Raspberry Pi to install the software:

pi@raspberrypi:~ $ wget http://www.uugear.com/repo/WittyPi4/install.sh
pi@raspberrypi:~ $ sudo sh install.sh



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.


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.


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.


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.


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.


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.

Technical Details

Revision History:

As of Feb 6th, 2024 -  The design of the board has been updated to the Rev C model.

  • For product support, please visit the UU tech support forum here.


Dimension65mm x 30mm x 4mm
Weight9g (net weight without accessories)
MicrocontrollerATtiny841 (datasheet)
Realtime ClockPCF85063A (datasheet), calibrated in factory.
Temperature SensorLM75B (datasheet)
MOSFET SwitchAO4620 (datasheet)
Super Capacitor0.07F
Power InDC 5V (via USB type C connector) or 5V in unpopulated header P2
Output CurrentUp to 2.5A for Raspberry Pi and its peripherals
Standby Current~0.5mA
Operating EnvironmentTemperature -30°C~80°C (-22°F~176°F)
Humidity 0~80%RH, no condensing, no corrosive gas
RoHS 2 2011 65 EU Compliant
RoHS 2 2015 863 EU Compliant