Code used on an ESP32 for green satnogs station.

main.c

#include <Arduino.h>
#include <HTTPClient.h>
#include <ArduinoJson.h>
#include <time.h>
#include <sys/time.h>

#define SSID ""
#define PASSWORD ""
#define NTPSERVER "pool.ntp.org"
#define TOKEN "Token API_KEY" 
#define STATION_ID 0
#define SHUTDOWN_PIN 4
#define BOOT_PI 15
#define STATUS_LED 2
#define DELAY 1000*180
#define TIME_BEFORE_BOOT 300

void shutdownPi();


DynamicJsonDocument doc(32862/4); //For reading JSON
struct tm tempTM; //Temp Time
HTTPClient http; //HTTPClient instance

time_t EndofObs; //Time for saved end of obs
time_t StartofObs; //TIme for saved start of obs
bool piStatus = false; //Status of the Pi running or not.


 
time_t getTimeFromStringTime(String str) //Converts the string time from the json to a time_t
{
  char char_array[str.length() + 1];
  str.toCharArray(char_array, str.length() + 1);
  int Year, Month, Day, Hour, Minute, Second ;
  sscanf(char_array, "%d-%d-%dT%d:%d:%dZ", &Year, &Month, &Day, &Hour, &Minute, &Second); 
  tempTM.tm_year = Year-1900;
  tempTM.tm_mon = Month-1;
  tempTM.tm_mday = Day;
  tempTM.tm_hour = Hour;
  tempTM.tm_min = Minute;
  tempTM.tm_sec = Second;
  time_t t = mktime(&tempTM);
  return t;
}

time_t getTimeTill(time_t t){ //Get the time between now and the passed in time
  time_t now;
  time(&now);
  return t-now;
}


void setup() {
  Serial.begin(9600);
  delay(1000);

 
  WiFi.begin(SSID, PASSWORD); //Connect to wifi
  delay(1000);
 
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi..");
  }
  configTime(0, 0, NTPSERVER); //Configure the time server.
 
  Serial.println("Connected to the WiFi network");
  
  EndofObs = -700;
  StartofObs = 0;

  //Init pinModes and states
  pinMode(BOOT_PI, OUTPUT);
  pinMode(SHUTDOWN_PIN,OUTPUT);
  pinMode(STATUS_LED,OUTPUT);
  pinMode(5,OUTPUT);
  digitalWrite(BOOT_PI,HIGH);
  digitalWrite(SHUTDOWN_PIN,HIGH);
  shutdownPi();
}

void loop() {
  digitalWrite(STATUS_LED,HIGH);
  
   
   http.begin("https://network.satnogs.org/api/jobs/?format=json&ground_station="+STATION_ID); //Specify the URL and certificate
   http.addHeader("Authorization",TOKEN); //Add the header to mark station as online
  int httpCode = http.GET();
  if (httpCode > 0) { //Check for the returning code

   String payload = http.getString();
   deserializeJson(doc,payload); //Get the json from jobs
   JsonArray array = doc.as<JsonArray>(); //Array of Jobs
   if(array.size() > 0){
   JsonVariant obs = array.getElement(array.size()-1); //Get the first job
   JsonVariant start = obs["start"]; //Get its start time
   JsonVariant end = obs["end"]; //Get its end time
   time_t startTime = getTimeFromStringTime(start.as<String>()); //Convert to time_t
   time_t endTime = getTimeFromStringTime(end.as<String>()); //Convert to time_t
   if((getTimeTill(StartofObs) < 0) & (getTimeTill(EndofObs) < -(TIME_BEFORE_BOOT*2))){ //Should update current start and end
     StartofObs = startTime;
     EndofObs = endTime;
     if(((getTimeTill(startTime) > 1800  ) & piStatus)){ // Is time to next obs large?
        shutdownPi(); //Shutdown
        piStatus = false;
     }
   }

    if((getTimeTill(startTime) < TIME_BEFORE_BOOT) & (getTimeTill(EndofObs) > 0) & !piStatus){ //Does the pi need to run.
      piStatus = true;
      Serial.print("Starting Pi: ");
      time_t now;
      time(&now);
      Serial.println(now);
      digitalWrite(5,HIGH);
      digitalWrite(BOOT_PI,LOW);
      delay(1000);
      digitalWrite(BOOT_PI,HIGH);
    }
    

  }else{
    if((getTimeTill(StartofObs) < 0) & (getTimeTill(EndofObs) < -(TIME_BEFORE_BOOT*2)) & piStatus){ //Shut down if not and obs over
     
        shutdownPi();
        piStatus = false;
     
   }
  }

}
 
else {
   Serial.print("Error on HTTP request. Error Code: ");
   Serial.println(httpCode);
}
Serial.print(".");
http.end(); //Free the resources
digitalWrite(STATUS_LED,LOW);
delay(DELAY);
}


void shutdownPi(){
  Serial.print("Stopping Pi: ");
        time_t now;
        time(&now);
        Serial.println(now);
        piStatus = false;
        digitalWrite(SHUTDOWN_PIN,LOW);
        delay(1000);
        digitalWrite(SHUTDOWN_PIN,HIGH);
        digitalWrite(5,LOW);
}