Exercise 9: RTC and data logging

Introduction

The ESP32 has a real time clock implemented on chip. This will however only work as long as the ESP32 is powered. It may therefore be interesting to employ and external RTC like the DS1307, backed up with a battery, to keep time even when the ESP32 is powered off or in deep sleep mode.

Getting the current (GMT) time from the internet is easy when using the ntptime module. We can make use of this to setup our RTC with the correct time.

Exercise 1: Set the ESP32 RTC

Ask the user for the current date and time and set the real time clock in the ESP32 correspondingly. Read back the time a little later and print it out. Use a parser similar to the one we wrote in session 1, exercise 2, for the calculator to check the user input.

The driver for the ESP32 RTC is described in https://docs.micropython.org/en/latest/esp32/quickref.html#real-time-clock-rtc.

Be careful about the parameters passed into rtc.datetime. These are yyyy mm dd ww hh mm ss us where

• yyyy: 4 digits for the year
• mm: 2 digits for the month
• dd: 2 digits for the day
• ww: 2 digits for the day in the week. In fact these data do not seem to be used!
• hh: the hour
• mm: minutes
• ss: seconds
• us: microseconds (I always put these to 0)

https://artofmemory.com/blog/how-to-calculate-the-day-of-the-week-4203.html

In my solutions I wrote a module esp32RTC with the following functions:

• rtcSetUserTime(): This asks the user for date and in in the form yyyy mm dd hh mm ss
  It the calls parse, another function of the esp32RTC module checking user input and parsing it.
  rtcSetUserTime finally create a machine.RTC instance and sets the RTC with rtc.datetime()
• rtcSetTime(year,month,day,hours,minutes,secs)
• rtcGetTime() returning the current time as a tuple (yyyy,mm,dd,hh,mm,ss)
• dayOfWeek(year,month,day) returning the code for the weekday (0=sun,6=sat)
• dayOfWeekString(dayCode) returning a humanly readable string to the day of the week: "sun"..."sat"

Here is a screen dumps showing a session controlling the ESP32 RTC:

Exercise 2: Set the DS1307 RTC

Do the same thing with the DS1307 RTC

Exercise 3: Get the time from the Internet and setup the RTC

Write a function that connects your ESP32 to the Internet through WiFi. Use the station interface to do so. Find out the IP address the ESP32 can be reached at. Setup system time and print it.

-- Uli Raich - 2020-05-06

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