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edited Jul 5, 2017 at 2:24

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EDIT:
I don't have an LCD screen, so I didn't test the code with an LCD, but the code that just dumps the parsed data back to serial works.

//#include <LiquidCrystal.h>
#include <ArduinoJson.h>

const struct LCDPos {
  uint8_t x;
  uint8_t y;
} lcd_pos[] = {
  {0, 0},
  {8, 0},
  {0, 1},
};

//LiquidCrystal lcd(12, 11, 7, 6, 5, 4);

void setup() {
  Serial.begin(115200);
  //lcd.begin(16, 2);
}

void loop() {
  StaticJsonBuffer<100> jsonBuffer;
  JsonObject& root = jsonBuffer.parseObject(Serial);
  if (root == JsonObject::invalid())
    return;

  Serial.println("JSON received");
  uint8_t i = 0;
  for (JsonObject::iterator it = root.begin(); it != root.end() && i < (sizeof(lcd_pos) / sizeof(lcd_pos[0])); ++it, i++)
  {
    //lcd.setCursor(lcd_pos[i].x, lcd_pos[i].y);
    //lcd.print(it->value.asString());
    Serial.print(i);
    Serial.print(':');
    Serial.print(lcd_pos[i].x);
    Serial.print(',');
    Serial.print(lcd_pos[i].y);
    Serial.print(' ');
    Serial.println(it->value.asString());
  }
  Serial.println();
}

If I send

{"TPS":"0.40","MAP":"0.95","LOAD":"14"}{"LOAD":"2.40","RPM":"4200","INJECTION_TIME":"4.87"}

over the serial, it returns

JSON received
0:0,0 0.40
1:8,0 0.95
2:0,1 14

JSON received
0:0,0 2.40
1:8,0 4200
2:0,1 4.87

EDIT:
I don't have an LCD screen, so I didn't test the code with an LCD, but the code that just dumps the parsed data back to serial works.

//#include <LiquidCrystal.h>
#include <ArduinoJson.h>

const struct LCDPos {
  uint8_t x;
  uint8_t y;
} lcd_pos[] = {
  {0, 0},
  {8, 0},
  {0, 1},
};

//LiquidCrystal lcd(12, 11, 7, 6, 5, 4);

void setup() {
  Serial.begin(115200);
  //lcd.begin(16, 2);
}

void loop() {
  StaticJsonBuffer<100> jsonBuffer;
  JsonObject& root = jsonBuffer.parseObject(Serial);
  if (root == JsonObject::invalid())
    return;

  Serial.println("JSON received");
  uint8_t i = 0;
  for (JsonObject::iterator it = root.begin(); it != root.end() && i < (sizeof(lcd_pos) / sizeof(lcd_pos[0])); ++it, i++)
  {
    //lcd.setCursor(lcd_pos[i].x, lcd_pos[i].y);
    //lcd.print(it->value.asString());
    Serial.print(i);
    Serial.print(':');
    Serial.print(lcd_pos[i].x);
    Serial.print(',');
    Serial.print(lcd_pos[i].y);
    Serial.print(' ');
    Serial.println(it->value.asString());
  }
  Serial.println();
}

If I send

{"TPS":"0.40","MAP":"0.95","LOAD":"14"}{"LOAD":"2.40","RPM":"4200","INJECTION_TIME":"4.87"}

over the serial, it returns

JSON received
0:0,0 0.40
1:8,0 0.95
2:0,1 14

JSON received
0:0,0 2.40
1:8,0 4200
2:0,1 4.87

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answered Jul 1, 2017 at 0:59

gre_gor

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If you want to read 3 values of a object that you don't know the names of the key, you can use an iterator as shown in the ArduinoJson library's docs.

And as already mentioned in the comments, you can also replace all the serial reading code with just Serial passed into the jsonBuffer.parseObject function.

#include <LiquidCrystal.h>
#include <ArduinoJson.h>

const struct LCDPos {
  uint8_t x;
  uint8_t y;
} lcd_pos[] = {
  {0, 0},
  {8, 0},
  {0, 1},
};

LiquidCrystal lcd(12, 11, 7, 6, 5, 4);

void setup() {
  Serial.begin(115200);
  lcd.begin(16, 2);
}

void loop() {
  StaticJsonBuffer<100> jsonBuffer;
  JsonObject& root = jsonBuffer.parseObject(Serial);
  if (root == JsonObject::invalid())
    return;
  
  uint8_t i = 0;
  for (JsonObject::iterator it = root.begin(); it != root.end() && i<(sizeof(lcd_pos)/sizeof(lcd_pos[0])); ++it, i++)
  {
    lcd.setCursor(lcd_pos[i].x, lcd_pos[i].y);
    lcd.print(it->value.asString());
  }
}

You will need to make sure, that the values are sent in the order that you want them on your LCD.