Witty Pi 4 Mini: Realtime Clock and Power Management for Raspberry Pi

Witty Pi 4 Mini is the fourth generation of Witty Pi, and it is the upgraded version of Witty Pi 3. It adds real-time clock (RTC) and power management to your Raspberry Pi and can define complex ON/OFF sequences with a simple script. Witty Pi 4 mini supports all Raspberry Pi models with a 40-pin header such as 4B, 3B+, 3B, 3A+, 2B, B+, A+, Zero, Zero W.

• Factory calibrated and temperature compensated real-time 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 a very similar design to 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 REAL-TIME CLOCK AND ON/OFF SCHEDULING

The real-time 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 to ±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 a 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 are powered by a 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 a 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.

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 the background will execute the shutdown command before the power gets cut, and it avoids the data corruption caused by a “hard” shutdown.

Witty Pi 4 Mini 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 Witty Pi.

SINGLE I2C DEVICE

Witty Pi 4 Mini uses MCU to emulate a single I2C device with default address 0x08 and also maps all I2C registers in real-time clock and temperature sensor as virtual I2C registers in the same device. You can access all I2C registers in real-time clock and temperature sensors via the single I2C device emulated by Witty Pi 4.

The advantage of this new design is that Witty Pi 4 Mini hides other I2C devices (real-time clock, temperature sensor) and becomes the proxy for them to talk to Raspberry Pi. Because the I2C address used by Witty Pi 4 mini 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 your Witty Pi 4 Mini on any device that has 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.

Specifications

• Dimension: 65mm x 30mm x 4mm (Approx.)
• Weight: 9g (net weight without battery)
• Microcontroller: ATtiny841
• Realtime Clock: PCF85063A 
• Temperature Sensor: LM75B 
• MOSFET Switch: AO4620 
• Power In: DC 5V (via USB type C connector) or DC 6V~30V (via XH2.54 connector)
  
• Output Current: Up to 2.5A for Raspberry Pi and its peripherals
  
• Standby Current: ~0.5mA
  
• Operating Environment: Temperature -30°C~80°C (-22°F~176°F) and Humidity 0~80%RH, no condensing, no corrosive gas

Kit Content

• 1 x Witty Pi 4 Mini Board 
  
• 4 x M2.5x10mm Plastic Screws
  
• 4 x 4mm Plastic Spacer
  
• 4 X M2.5 Plastic Nut

Note: Raspberry Pi & other items are not included!