UUGear Witty Pi 4 User manual

Copyright © 2023 Dun Cat B.V., All rights reserved.
UUGear is a trade name of Dun Cat B.V.
Witty Pi 4:
Realtime Clock and Power Management for Raspberry Pi
User Manual (revision 1.02)

Copyright © 2023 Dun Cat B.V., All rights reserved.
UUGear is a trade name of Dun Cat B.V.
Table of Contents
1. Product Overview..............................................................................................................1
1.1 Accurate Realtime Clock and ON/OFF Scheduling................................................1
1.2 Temperature Controlled Device..............................................................................2
1.3 DC/DC Converter and e-Latching Power Switch....................................................3
1.4 Interface Introduction.............................................................................................4
2. Specification / Technical Details.........................................................................................5
3. Package Content...............................................................................................................5
4. How Does Witty Pi Work?..................................................................................................6
5. Software Installation, Updating and Uninstallation.............................................................7
5.1 Install Software......................................................................................................7
5.2 Update Software....................................................................................................7
5.3 Uninstall Software..................................................................................................7
6. Mounting Witty Pi 4 on Raspberry Pi.................................................................................8
7. Software Usage...............................................................................................................11
7.1 Write system time to RTC....................................................................................11
7.2 Write RTC time to system ....................................................................................12
7.3 Synchronize time.................................................................................................12
7.4 Schedule next shutdown......................................................................................12
7.5 Schedule next startup..........................................................................................12
7.6 Choose Schedule Script ......................................................................................12
7.7 Set low voltage threshold.....................................................................................13
7.8 Set recovery voltage threshold.............................................................................13
7.9 Set over temperature action.................................................................................14
7.10 Set below temperature action ..............................................................................14

Copyright © 2023 Dun Cat B.V., All rights reserved.
UUGear is a trade name of Dun Cat B.V.
7.11 View/change other settings..................................................................................14
7.12 Reset Data… .......................................................................................................15
7.13 Exit ......................................................................................................................16
8. Using UWI (UUGear Web Interface)................................................................................17
9. About Schedule Script.....................................................................................................18
9.1 How does Schedule Script Work?........................................................................18
9.2 Make Your Own Schedule Script..........................................................................20
9.3 Using Schedule Script Generator.........................................................................22
9.4 Advanced Usage of Schedule Script....................................................................23
10. Know More about the Realtime Clock..........................................................................24
10.1 CR2032 Battery and Time Keeping......................................................................24
10.2 Alarms and Alarm Output.....................................................................................24
10.3 Temperature Compensation.................................................................................24
11. Additional Interfaces....................................................................................................26
11.1 The Unpopulated 3-Pin Header (P2)....................................................................26
11.2 The Unpopulated 7-Pin Header on the Top (P3) ..................................................26
11.3 The Unpopulated 2 x 3 Pin Headers (P4).............................................................28
11.4 The Unpopulated 7-Pin Header on the Left (P5)..................................................29
11.5 The Unpopulated 2-Pin Header (P6)....................................................................30
12. Integrate with Other Programs.....................................................................................31
13. Migrating from Witty Pi 3 to Witty Pi 4..........................................................................33
14. Witty Pi Log Files.........................................................................................................35
15. Frequently Asked Questions (FAQ) .............................................................................36
15.1 What I2C address is used by Witty Pi 4? Can I change it?...................................36
15.2 What I2C Registers are provided by Witty Pi 4? ...................................................37
15.3 What GPIO Pins Are Used by Witty Pi4? .............................................................44
15.4 Is Witty Pi 4 Compatible with “Other Hardware”? .................................................45

Copyright © 2023 Dun Cat B.V., All rights reserved.
UUGear is a trade name of Dun Cat B.V.
15.5 Witty Pi 4 does not boot?.....................................................................................45
15.6 Why Raspberry Pi Immediately Turns On after Shutdown?..................................48
16. Revision History...........................................................................................................49

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1. Product Overview
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 ±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.
1.1 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 ±2ppm (about 1 minute per year). 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

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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 work much longer with Witty Pi installed.
1.2 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.

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

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1.4 Interface Introduction
Witty Pi 4 supports all Raspberry Pi models that has the 40-pin GPIO header, including A+, B+, 2B,
Zero, Zero W, Zero 2W, 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.
The picture below shows the available interfaces of Witty Pi 4.
1. USB type C connector for 5V power input (5V)
2. XH2.54 connector for higher voltage input (VIN)
3. Unpopulated power header with VIN, 5V and GND
4. White LED as status indicator
5. On/off switch
6. 2x20 pin stacking header for connecting to Raspberry Pi
7. ICSP header for uploading firmware
8. 3V (CR2032) battery holder
9. Unpopulated external 3V battery connector
10. Unpopulated 7-pin header for internal I2C bus and extra signals
11. Unpopulated 7-pin header for extension or integration

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2. Specification / Technical Details
Dimension
65mm x 56mm x 19mm
Weight
23g (net weight without accessories)
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 only, when no power supply is connected)
Power In
DC 5V (via USB type C connector) or DC 6V~30V (via XH2.54 connector)
Output Current
Up to 3Afor 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
3. Package Content
Each package of Witty Pi 4 contains:
Witty Pi 4 board x 1
30cm 22AWG XH2.54 cable x 1
M2.5x11 copper standoff x 4
M2.5 screws x 8
* Since February 2023, the CR2032 battery is replaced by the 30 cm XH2.54 cable.

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4. How Does Witty Pi Work?
The diagram below shows the basic workflow of how Witty Pi turns on/off your Raspberry Pi.
After you tap the button on Witty Pi, it powers your Raspberry Pi via the GPIO header, and your
Raspberry Pi will boot. Witty Pi’s software will run automatically after boot, which will send the
SYS_UP signal (via GPIO-17) to Witty Pi. Witty Pi’s firmware receives the SYS_UP signal and starts
to listen to Raspberry Pi’s TXD pin (GPIO-14). If you shut down your Raspberry Pi (running shutdown
command or choose “Shutdown” in GUI), the TXD pin will go LOW and Witty Pi will cut the power
after some delay. If you tap the button again, that equals to shorting GPIO-4 to GND, and Witty Pi’s
software will run shutdown command for you.
Witty Pi has realtime clock (RTC) onboard and it always knows the time. You can schedule the
shutdown and startup of your Raspberry Pi, which are implemented with two alarms. When the alarm
is triggered, Witty Pi’s firmware will emulate a “button clicking”, which will turn on/off your Raspberry
Pi accordingly. You can either configure single alarm for shutdown and/or startup, or you can define a
simple script to plan a rather complex on/off sequence for your Raspberry Pi.
Witty Pi has Analogue to Digital Converter (ADC) in its microcontroller (MCU), which can measure
the input voltage (via the white XH2.54 connector). If the voltage is dropped below the preset
threshold, Witty Pi’s firmware will emulate a “button clicking” to turn off your Raspberry Pi. If the
voltage is raised above the preset threshold, Witty Pi’s firmware will emulate another “button clicking”
to turn on your Raspberry Pi again. This allows you to turn off/off your Raspberry Pi according to
input voltage.
Witty Pi also has temperature sensor onboard. If the temperature rises over the preset threshold,
Witty Pi’s firmware can emulate a “button clicking” to turn off or turn on your Raspberry Pi. If the
temperature drops below the preset threshold, Witty Pi can also turn on/off your Raspberry Pi. You
can define the complete logic according to your needs, and turn your Raspberry Pi to a
temperature-controlled device.