Merge branch 'master' of https://github.com/CDFER/PCF8563_Library

README.md

@@ -2,14 +2,13 @@ pcf8563-RTC
 =====================================
 A library to interace esp chips with the NXP PCF8563 Real time clock (RTC) in the arduino (c++) Framework.
 
-
 ## Features
 - use multiple I2C Busses -> rtc.begin(Wire1);
 - works with timezones (RTC is set to UTC)
 https://github.com/nayarsystems/posix_tz_db/blob/master/zones.csv
 - set System (ESP32) time from RTC (assumes RTC is set to UTC/GMT)
 - set RTC time from System (epoch)
-- Set RTC time over wifi example
+- Set RTC time using wifi example
 
 ## Warnings
 - not all functions are implemented
@@ -24,7 +23,6 @@ https://github.com/nayarsystems/posix_tz_db/blob/master/zones.csv
 PCF8563_Class rtc;
 const char *time_zone = "NZST-12NZDT,M9.5.0,M4.1.0/3";	// https://github.com/nayarsystems/posix_tz_db/blob/master/zones.csv
 
-
 Wire.begin();
 rtc.begin(Wire);
 setenv("TZ", time_zone, 1);
@@ -40,11 +38,18 @@ Serial.print(&timeinfo, "%d/%m/%y %H:%M:%S");
 
 ## 🖼️ Schematic
 ![Schematic](/images/schematic.png)
-
-
+- uses a cr1220 coincell (though almost any 3v lithium coincell should work)
+- to not discharge the battery too fast disable output clock and alarms
+- Low backup current: typical 0.25 uA at 3.0 V (theoretical not tested)
+- currently I'm testing with 4.7kohm pullups on sda and scl
+- currently the crystal I'm using is a Seiko Epson Q13FC1350000400 (+-20ppm)
+- in theory this setup will drift by a maximum of ~11mins per year (https://www.analog.com/en/design-center/interactive-design-tools/real-time-clock-calculator.html)
+- in theory a 37mAh cr1220 battery will last ~14 years without any charging (incl battery self discharge)
+- 3.3V -> diode -> resistor charging of a coincell from 3.3v is hotly debated as to wether is good, ok, or horificly bad idea. I have not had any issuses but your mileage may vary
+- be careful with pcb placement (have the crystal as close to the RTC chip a possible and souround it with ground planes connected with vias)
 
 ## Based on the awesome work of Lewis he
-Origin created by Lewis he on April 1, 2019.
+Origin created by Lewis he in 2019
 https://github.com/lewisxhe/PCF8563_Library
 
-MIT license, all text above must be included in any redistribution
+MIT license