Witty Pi 4 - Real-time Clock and Power Management for Raspberry Pi

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The Witty Pi 4 is an add-on board that adds a real-time clock and power management to your Raspberry Pi. It can define your Raspberry Pi’s ON/OFF sequence and significantly reduce energy usage.

Witty Pi 4 is the fourth generation of the Witty Pi and has these hardware resources onboard:

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

We also stock the Witty Pi 4 Mini, with the same features minus the DC/DC converter, and uses a supercapacitor instead of a battery, with a much smaller footprint!


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Accurate Real-time Clock and On/Off Scheduling

The real-time 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 to 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 scheduled script to schedule complicated ON/OFF sequences 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 are powered by batteries. 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 making the RTC more accurate.

You can also specify the action (startup or shutdown) when the temperature goes above or below the preset threshold. This 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 a 6~30V power supply. You can also power your device with 5V 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 the background will execute the shutdown command before the power gets cut, this avoids the data corruption caused by a hard shutdown.

Witty Pi 4 supports all Raspberry Pi models that have 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 the Zero/Zero W/Zero 2 W model beforehand, so they can make a reliable connection with the Witty Pi.

Single I2C Device

Witty Pi 4 uses MCU to emulate a single I2C device with default address 0x08 and also maps all I2C registers in the real-time clock and temperature sensor as virtual I2C registers in the same device. You can access all I2C registers in the real-time 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 (real-time clock, temperature sensor) and becomes the proxy for them to talk to the 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, and you can access your Witty Pi 4 on any device that has network access.

Software Installation

You just need to run these two commands in your Raspberry Pi to install Witty Pi 3’s software:

wget https://www.uugear.com/repo/WittyPi4/install.sh
sudo sh install.sh

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

Package Contents

Each Witty Pi 4 package contains:

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

Specifications

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

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