USB-RTC

USB RTC

USB RTC is an open source real time clock device that comprises MCP2221, a USB-to-UART/I2C serial converter, which enables USB connectivity, in the processes that include a USB, UART(Serial), GPIO, and I2C interfaces. It runs on Hi-tech DS3231 RTC chip, an accurate I2C, runs the USB RTC with extremely high efficiency at a low cost. USB RTC for Raspberry Pi has cross platform support which makes it enable to work on different platforms like Windows, MAC, etc.

Features

Temperature-compensated crystal oscillator

DS3231 advanced processor

MCP2221

I2C/SMBus supported clock and data lines

User-selectable via jumper cable for 3.3V or 5V level output (up to 500 mA)

Four GPIO lines that are configurable for GPIO Operations

Pins for Serial(UART) Communication

Supports full-speed USB (12 Mb/s)

64-byte Transmit

64-byte Receive

USB 2.0 Compliant

Low-Power Consumption

Specifications

Accuracy ±2ppm from 0°C to +40°C

Accuracy ±3.5ppm from -40°C to +85°C

Battery Backup Input for Continuous Timekeeping

Operating Temperature Ranges Commercial: 0°C to +70°C Industrial: -40°C to +85°C

Low-Power Consumption

Real-Time Clock Counts Seconds, Minutes, Hours, Day, Date, Month, and Year with Leap Year Compensation Valid Up to 2100

Two Time-of-Day Alarms

Programmable Square-Wave Output

Fast (400kHz) I2C Interface

3.3V Operation

Digital Temp Sensor Output: ±3°C Accuracy

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Installation

Raspberry Pi

Python

• Install MCP2221 Library by running below command on terminal:

sudo pip3 install PyMCP2221A

• Connect USB-RTC on USB Port of Raspberry Pi/Windows.
• Now clone/download USB-RTC Github Repository by running below command:

git clone https://github.com/sbcshop/USB-RTC.git

• Now enter downloaded folder from home/pi or by rnning below command:

cd USB-RTC

• Now run test.py file by running below command:

sudo python3 test.py

• After running above command, you will get below output.

Windows

Python

• Install MCP2221 Library by running below command on terminal:

pip install PyMCP2221A

• Connect USB-RTC on USB Port of Raspberry Pi/Windows.

• Now clone/download USB-RTC Github Repository of USB RTC:

https://github.com/sbcshop/USB-RTC

• Open the downloaded folder and run test.py file in any python supported ide.
• You will get the below output after running the file.

Functions

• To modify Date & Time, you have to change the last value of each line in the hexadecimal form inside def SetTime(address):

For Example :

#sec min hour week day month year
NowTime = [0x00,0x00,0x18,0x04,0x12,0x08,0x15]  #Edit this line to set RTC Date and Time

• To read time, you can call "ds3231ReadTime()" Function

• To read the internal temperature of USB-RTC, uncomment below the line by removing from start and end of the line :

'''Celsius = getTemp(address)
Fahrenheit = 9.0/5.0 * Celsius + 32
print (Fahrenheit, "*F /", Celsius, "*C") '''

Resources

MCP2221 Datasheet

Blogs

• Complete guide to setup automatic time of RPi with USB RTC