How to converte EPOCH time into time and date on Arduino?

Question

I have a question on how to convert EPOCH timestamps, which I receive as char*, into DD.MM.YYYY and HH:MM:SS format separately?

Here is more information on my Arduino project: The Arduino is receiving through an ESP8266 module three different EPOCH timestamps from the OpenWeatherMap API for sunrise, sunset and the current date. I want these 3 pieces of information to be displayed on a 1,3" OLED display, the date in DD.MM.YYYY and the other two timestamps in HH:MM format.

I was looking in several time libraries like TimeLib and RTC for a solution, but I wasn't able to find one.

That's my code fragment on receiving the timestamps:

DynamicJsonBuffer jsonBuffer(4096);
JsonObject& root = jsonBuffer.parseObject(client);
const char* date = root["dt"];
const char* sunrise = root["sys"]["sunrise"];
const char* sunset = root["sys"]["sunset"];

How to convert those timestamps?

Answer 1

Epoch are seconds from 1970年01月01日. Get it from JSON as unsigned long. They are a number in the returned JSON (no ")

from https://openweathermap.org/ doc:

"sys":{"country":"JP","sunrise":1369769524,"sunset":1369821049},

---

to convert it to string with TimeLib.h:

#include <TimeLib.h>
#include <ArduinoJson.h>
void setup() {
 Serial.begin(115200);
 const char* json = "{\"country\":\"JP\",\"sunrise\":1369769524,\"sunset\":1369821049}";
 DynamicJsonBuffer jsonBuffer;
 JsonObject& root = jsonBuffer.parseObject(json);
 unsigned long t = root["sunrise"];
 char buff[32];
 sprintf(buff, "%02d.%02d.%02d %02d:%02d:%02d", day(t), month(t), year(t), hour(t), minute(t), second(t));
 Serial.println(buff);
}
void loop() {
}

• dandavis: note you might need to divide the timestamp by 1000 if it includes ms, like JS's Dates for example.
• Juraj: @dandavis, I took the sample JSON from the openweathermap site
• dandavis: For sure, I'm just pointing out that there's two "epoc"s to be aware of from web services, in general.
• imax10000: For this example, it's not necessary to divide by 1000. Thank you very much for the help :)
• imax10000: @Juraj I have one more question to this topic: Can TimeLib also convert EPOCH timestamps to day names?(Monday, etc.)

Answer 2

I'm was having a similar challenge with my custom Wifi library m_wifi..cpp for the ESP32 ( see here )

After reading and googling I ended up coding the solution below:

ESP32Time rtc(0);
long int epochTime;
...
rtc.setTime( epochTime );
Serial.println( rtc.getDateTime(true) );

• Juraj: can it be used on a non esp32 Arduino as in the question?
• Miguel Tomás: yes. you can replicate the code to use on other than ESP32. Just need to find the compatible library for your specific MCU.