TFTMavLink

TFT onboard display for Arducopter/Pixhawk

Show informations with a cheap TFT Display 128x160 and arduino nano

This display is an extension of the onboard display SSD1306 the difference is the possibility to show more useful information for a complete pre-arm check.

The components required are :

• Display TFT 120x180 (ST7735)
• Arduino Nano
• Optional resistors for analog cell voltage input

How does it work ?

The mechanis is simple , a Mavlinkprocessor establish a comunication with a FlightController and require the stream messages.

void MavlinkProcessor::tryToConnectToAPM() {
	uint16_t len = 0;
	last_connection = (millis() - heartbeat_timer);
	if (millis() - heartbeat_timer > 1500UL) {
		heartbeat_timer = millis();
		if (true) {    // Start requesting data streams from MavLink
			digitalWrite(alive_led_pin, HIGH);
			//SYS STATUS -GPS
			mavlink_msg_request_data_stream_pack(0xFF, 0xBE, &msg, 1, 1,
					MAV_DATA_STREAM_EXTENDED_STATUS, 10,
					stream_flag.START_SYS_STATUS);
			len = mavlink_msg_to_send_buffer(buf, &msg);
			MavLinkSerial.write(buf, len);
			delay(10);

Once the connection is established , the processore read the messages and store the informations to the appropriate structure

 // MAVLINK_MSG_ID_VFR_HUD
	  //float   groundspeed;                // Current ground speed in m/s
	  //uint16_t   heading;                    // Current heading in degrees, in compass units (0..360, 0=north)
	  //uint16_t   throttle;                   // Current throttle setting in integer percent, 0 to 100
	  //int32_t    bar_altitude;               // 100 = 1m
	  //float    climb_rate;              // 100= 1m/s
	  mavlink_vfr_hud_t hud_raw;

	  //MAVLINK_MSG_ID_ATTITUDE
	  mavlink_attitude_t attitude;

	  // MAVLINK_MSG_ID_MISSION_CURRENT
	  uint16_t   mission_current_seq ;

	  //MAVLINK_MSG_ID_RC_CHANNELS_RAW
mavlink_rc_channels_raw_t rc_raw;

The class TFT implement the Adafruit library ,and provide with set of methods to write the data on the display

switch (mav_telemetry.gps_raw.fix_type) {
	case 0:
		strcpy(text, "No Fix");
		break;
	case 1:
		strcpy(text, "No Fix");
		break;
	case 2:
		strcpy(text, "2D Fix");
		break;
	case 3:
		strcpy(text, "3D Fix");
		break;
	}
	drawtext(text, ST7735_WHITE, ST7735_BLACK, 72, 24);
	drawtext(mav_telemetry.gps_raw.satellites_visible, ST7735_WHITE,
			ST7735_BLACK, 84, getCursorY() + offsY);
	drawtext(mav_telemetry.gps_raw.eph, ST7735_WHITE, ST7735_BLACK, 84,
			getCursorY() + offsY);
	drawtext((float) mav_telemetry.sys_status.voltage_battery / 1000.0,
			ST7735_WHITE, ST7735_BLACK, 2, 3, 84, getCursorY() + offsY);
	drawtext(mav_telemetry.status_text.text, ST7735_ORANGE, ST7735_BLACK, 0,
			getCursorY() + offsY);

actualScreen = PSYS;

The informations are showed on the page for fuctionality, a pushbutton is used to move around the pages. To improve the perfomance the strings are stored in the program space see Resource. it's very important to keep low the cycle time (100-300ms) for this reason every page start or stop a stream rate of messages. Only the relative message showed to the display is required.

The page Battery show up 4 cell voltage. A votage divided ratio is necessary to reference the voltage to 1.1V (internal reference Atmega328)

Shape W=60mm H=50mm

SYSTEM STATUS	HUD	RC CHANNEL	ATTITUDE
Armed/Disarmed	Heading	CH1....CH8 bargraph	Roll
GPS Status (Fix,no Fix ,ec..)	Groundspeed	RSSI	Pitch
GPS Sat/HDOP	Alt	...	Yaw
GPS number	Climb	...	Rollspeed
Message text	Throttle	...	Pitchspeed
...	...	...	Yawspeed

The enviroment used to build the project Eclipse Cpp 2018-09 with extension for Arduino program

Inspirated By MavlinkSmartPort