The module includes a DALLAS DS1307 chip constituting the Real Time Clock ( RTC ), as well as an ATMEL 24C32 EEPROM ( 4Kbytes )
The assembly generally communicates with any microcontroller-based system via the I²C bus
This module has 4 particularities:
- It does not have a 3V CR2032 Lithium battery, but a rechargeable lithium battery LIR2032 , as well as its charging circuit
- The address of the EEPROM memory is not modifiable because there are no coding jumpers
Pins A0, A1, A2 are connected to 0v. The binary address is therefore fixed at 1010000X (ie $ A0 in hexadecimal), where X is the R / W bit.
- The location of the resistance R7 ( quartz polarization in pin 2 ) is empty, it is normal and the module works perfectly like this
- The slot for U1 is empty, it can accommodate a temperature sensor ( not supplied ) “One-Wire” as a DALLAS DS1820 , or DS18B20 , etc …
I made measurements on the module, on 2 particular points:
- TP1: + 4,43V -> voltage at the terminals of the LIR2032 battery, with or without + 5V supply voltage !!!
This remains correct because indeed, the manufacturer of this battery indicates a nominal charge voltage of 4.20V with a constant current of 17mA, see the datasheet .
- TP2: + 3,195V -> the datasheet of DALLAS recommends a voltage V BAT between 2,0 and 3,5V
The voltage V BAT supplied to the DS1307 is therefore fully consistent with the manufacturer’s information, see the datasheet .
Fully charged, the battery can power the DS1307 to provide time ( date and time ) for 1 year.
The module can obviously be cascaded with other I²C devices, provided that we respect the addresses of each ( no duplicate addresses … ).
You can skip the rechargeable battery if it does not suit you, and replace it with a CR2032 battery, then proceed as follows:
- Remove resistors R7 / R4 / R5 / R6
- Replace the resistance R6 with a strap or R0
- Replace the LIR2032 battery with a CR2032 battery
Dimensions : 27 x 28 x 8.4mm (W x D x H)
→ I bought this module here in December 2015 for 1.12 € ( free shipping ).
Schematic diagram of the module that I redrawn under Eagle:
Source code to write date/hour, Read date, etc: