M5-RTC-Module

The M5-RTC-Mod is a real time clock specifically designed for the popular ESP32 based M5-Stack. It features the RV-3028-C7 RTC from Micro Crystal.

Features

high precision RTC with ±1ppm deviation per year (±32 seconds per year)
extremely long battery runtime with a CR2032 lithium cell (at least 10 Years, considering the operating life of the battery)
fully compatible to the M5Stack Core
two external EEPROMs
battery voltage monitoring through a 10-bit ADC.
configurable interrupt pin
3D printable housing for an M5Stack
all components are connected via a single I2C bus

Repository Contents

/examples – example sketches for the library
/src – source files for the library (.cpp, .h)
/extras/hardware – schematic, Gerber-files and bill of material
/extras/3D-files – .stl-file for 3D printing

The library is based on the RTC RV-3028-C7 Arduino Library. It also includes the uEEPROMLib for communication with the external EEPROM via I2C. The battery voltage is monitored using the MCP3X21 library.

API

The following functions are included in this library:

begin() – initializes the I2C-Interface and the RTC. Must be called in the setup function
setLocalTimeToRTC() – set the time on the ESP32 to the M5-RTC-Mod
getBatteryStatus() – returns true if the battery is ok, false if it's to low
getBatteryVoltage() – returns the battery Voltage in mV

This library works best in combination with functions from the included libraries:

Additional functions to control the RTC are described here. You can use these by adding .rtc to the call of the function.
Additional functions to control the EEPROM are described here. You can use these by adding .eeprom0 or .eeprom1 to the call of the function.
Additional functions to control the ADC are described here. You can use these by adding .adc to the call of the function.

Usage

Here is an example on how to use the library:

#include <M5_RTC_Module.h>

// create an instance of the class M5_RTC_Mod
M5_RTC_Mod rtc_mod;

void setup(){
    // init RTC-Module
    rtc_mod.begin()
}

void loop(){
    // Updates the time variables from RTC
    if (rtc_mod.rtc.updateTime()) {
        currentTime = rtc_mod.rtc.stringTimeStamp();
    } else {
        // RTC failed to update
    }
}

Choosing the interrupt pin

You can set up an interrupt event on the RTC. With the help of the solder jumper LJ1 on the M5-RTC-Mod board you can choose which IO of the ESP32 should act as an interrupt pin.

The following IOs can be chosen as an interrupt pin: