#Coding4Fun – How to control your #drone with 20 lines of code! (5/N)

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Coding4Fun Drone 🚁 posts

  1. Introduction to DJI Tello
  2. Analyzing Python samples code from the official SDK
  3. Drone Hello World ! Takeoff and land
  4. Tips to connect to Drone WiFi in Windows 10
  5. Reading data from the Drone, Get battery level
  6. Sample for real time data read, Get Accelerometer data
  7. How the drone camera video feed works, using FFMPEG to display the feed
  8. Open the drone camera video feed using OpenCV
  9. Performance and OpenCV, measuring FPS
  10. Detect faces using the drone camera
  11. Detect a banana and land!
  12. Flip when a face is detected!
  13. How to connect to Internet and to the drone at the same time
  14. Video with real time demo using the drone, Python and Visual Studio Code
  15. Using custom vision to analyze drone camera images
  16. Drawing frames for detected objects in real-time in the drone camera feed
  17. Save detected objects to local files, images and JSON results
  18. Save the Drone camera feed into a local video file
  19. Overlay images into the Drone camera feed using OpenCV
  20. Instance Segmentation from the Drone Camera using OpenCV, TensorFlow and PixelLib
  21. Create a 3×3 grid on the camera frame to detect objects and calculate positions in the grid
  22. Create an Azure IoT Central Device Template to work with drone information
  23. Create a Drone Device for Azure IoT Central
  24. Send drone information to Azure IoT Central
  25. Using GPT models to generate code to control the drone. Using ChatGPT
  26. Generate code to control the 🚁 drone using Azure OpenAI Services or OpenAI APIs, and Semantic Kernel

Hi!

Today is code time! In my previous post I share some code to send commands to the drone. Today I’ll show how to read the information from the drone. Before I start, someone asked if my kids are having fun with the drone. A image will be enough to answer this.

Reading drone information

So, as far as I understand, the drone is constantly sending information to the connected client. That’s why we have the following function running all the time in a separate thread:

def receiveData():
    global response
    while True:
        try:
            response, _ = clientSocket.recvfrom(1024)
        except:
            break
# ... more code
response = None
recThread = threading.Thread(target=receiveData)
recThread.daemon = True
recThread.start()

The response is stored in a global variable named response. And it’s very easy to understand the information that we the drone sends back. This is a sample received data.

pitch:0;roll:1;yaw:0;vgx:0;vgy:0;vgz:0;templ:79;temph:82;tof:10;h:0;bat:39;baro:50.42;time:0;agx:-8.00;agy:-17.00;agz:-999.00

As you can read, all the information is condensed in a single line and we can split and get:

  • pitch
  • roll
  • yaw
  • vgx
  • vgv
  • vgz
  • templ (temperature low)
  • temph (temperature high)
  • tof (time of flight)
  • h (height)
  • b (battery)
  • baro (barometer)
  • time
  • agx
  • agy
  • agz

In python this is a simple routine, and after split this into a list, the battery value is on index 21:

ls = 'pitch:0;roll:1;yaw:0;vgx:0;vgy:0;vgz:0;templ:79;temph:82;tof:10;h:0;bat:39;baro:50.42;time:0;agx:-8.00;agy:-17.00;agz:-999.00'
>>> ls1 = ls.replace(';', ':').split(':')
>>> ls1
['pitch', '0', 'roll', '1', 'yaw', '0', 'vgx', '0', 'vgy', '0', 'vgz', '0', 'templ', '79', 'temph', '82', 'tof', '10', 
'h', '0', 'bat', '39', 'baro', '50.42', 'time', '0', 'agx', '-8.00', 'agy', '-17.00', 'agz', '-999.00']
>>> ls1[21]
'39'
>>>

So with this, to get the battery level of the drone will require this code:

# Bruno Capuano
# get drone battery demo
import socket
import time
import threading
def sendCommand(command):
global response
timestamp = int(time.time() * 1000)
clientSocket.sendto(command.encode('utf-8'), address)
while response is None:
if (time.time() * 1000) – timestamp > 5 * 1000:
return False
return response
def sendReadCommand(command):
response = sendCommand(command)
try:
response = str(response)
except:
pass
return response
def sendControlCommand(command):
response = None
for i in range(0, 5):
response = sendCommand(command)
if response == 'OK' or response == 'ok':
return True
return False
def receiveData():
global response
while True:
try:
response, _ = clientSocket.recvfrom(1024)
except:
break
def readStates():
global battery
while True:
try:
response_state, _ = stateSocket.recvfrom(256)
if response_state != 'ok':
response_state = response_state.decode('ASCII')
list = response_state.replace(';', ':').split(':')
battery = int(list[21])
except:
break
# ———————————————–
# Main program
# ———————————————–
# connection info
UDP_IP = '192.168.10.1'
UDP_PORT = 8889
last_received_command = time.time()
STATE_UDP_PORT = 8890
address = (UDP_IP, UDP_PORT)
response = None
response_state = None
clientSocket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
clientSocket.bind(('', UDP_PORT))
stateSocket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
stateSocket.bind(('', STATE_UDP_PORT))
# start threads
recThread = threading.Thread(target=receiveData)
recThread.daemon = True
recThread.start()
stateThread = threading.Thread(target=readStates)
stateThread.daemon = True
stateThread.start()
# drone information
battery = 0
# connect to drone
sendControlCommand("command")
# get and display battery
sendReadCommand('battery?')
time.sleep(5)
print(f'Battery: {battery} %')
view raw DjiTelloGetBattery.py hosted with ❤ by GitHub

The output is not very amazing, but it works!

powershell console displaying the drone battery level.

Happy coding!

Greetings

El Bruno

More posts in my blog ElBruno.com.

More info in https://beacons.ai/elbruno

References

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