The Longan RTC card is based on the DS1307 chip, which supports the I2C protocol. The card requires a Lithium cell battery (CR1225) to operate a long period continuously.
The clock provides the following parameters:
The RTC card also provides a calendar with the following parameters:
The clock operates in either the 24-hour or 12-hour format with AM/PM indicator. The card requires to insert 3V CR1225 lithium cell battery into the battery holder.
- Supports two wire I2C bus interface
- 30 pin gold fingers
- DS1307 chip
- ATmega 168PA microprocessor - runs card firmware.
- LED indicator – flashes when Carduino read/write data from/to the card through I2C.
- Operating Voltage: 5V
- Battery Voltage：2.0-3.5 V
The default I2C address is printed on the back side of the card which is 0x0C. However, you can change it to a different address with the card firmware (Read our wiki for how to change the default I2C address of a card.).
The edge connector (gold fingers) has total of 30 contacts (each side has 15 contacts).
On the front side of the RTC card, a white arrow is printed near the edge connector indicates the pin #1. You can find some pin numbers printed on the edge connector itself (1, 15, and 29). You can count the pin numbers starting with 1 and count by twos from right to left would be 1, 3, 7, 9, 11, 15, 17, 19, 21, 23, 27, and 29. Notice that all the counts are odd numbers.
On the back side of the RTC card, you also can find some pin numbers printed on the edge connector itself (2, 16, and 30). You can count the pin numbers starting with 2 and count by twos from left to right would be 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28 and 30. Notice that all the counts are even numbers.
Among the 30 pins, following pins can be used for I2C communication.
- SDA: Digital I/O, I2C bus serial bidirectional data line (Front: pin #5, #25 / Back: pin #6, #26)
- SCL: Digital Input, I2C bus serial clock input (Front: pin #7, #23 / Back: pin #8, #24)
Also, following pins connect with the common power bus of the board.
- VCC: Power supply (Front: pin #1, #29 / Back: pin #2, #30)
- GND: To be connected to the system ground (Front: pin #3, #27 / Back: pin #4, #28)
How to Use¶
The RTC card can be plugged into an edge connector slot of one of the following Longan boards.
- Game board
- Car board
- Sensor board
- Extension board
- PI Hap
When you plug, the white arrow head printed on the card should be pointing toward the white arrow head printed near the edge connector slot of the board. Once plugged, it can communicate with the Carduino through the I2C bus line of the board. It will also connect to the common power bus of the board.