Lag in fetching serial data from Arduino

Question

I am working on a project based on Arduino and python3.6,two HC-SR04 sense the distance of palms and process the data using Arduino and send it through serial port to python3.6 ,python3.6 with the help of pyserial ,pyautogui based on data from arduino controls a game named supertuxcart,a racing game,basically the thought behind this is controlling game with palms instead of keyboard or mouse .But the problem am facing is Arduino takes the distance measurement data from two HC-SR04(one for each hand) ultrasonic sensors, processes according and sends processed data through serial port to python3.6 ,there while running the my python script i open the game to check if its working ,it works, but there is lag in data received from arduino thus turn the game messy.

here is arduino code am using with NewPing library

#include <NewPing.h>
int trig1=9;
int echo1=6;
int trig2=7;
int echo2=5;
int R;
int L;
NewPing right(9,6,100);
NewPing left(7,5,100);
void setup() {
 pinMode(9,OUTPUT);
 pinMode(8,OUTPUT);
 pinMode(6,INPUT);
 pinMode(5,INPUT);
}
void loop() {
 Serial.begin(9600);
 //Serial.println("hi,am arduino");
 R=right.ping_cm();
 L=left.ping_cm();
 //Serial.println(R);
 //Serial.println(L);
 delay(0000);
 if (R==0 && L==0){
 Serial.println('0');
 }
 else if(R<L&&L-R>5){
 Serial.println('1');
 }
 else if(R>L&&R-L>5){
 Serial.println('2');
delay(3000);
 }
}

Here is python3.6 code am using

import serial
import pyautogui
import time
Arduino = serial.Serial('/dev/ttyACM0', 9600)
time.sleep(0)
print(Arduino.readline())
pyautogui.keyDown('up')
while 1:
 Data = Arduino.readline()
 print(Arduino.readline())
 if Data == b'0\r\n':
 pyautogui.keyUp('up')
 pyautogui.keyUp('right')
 pyautogui.keyUp('left')
 break
 elif Data == b'1\r\n':
 pyautogui.keyUp('left')
 pyautogui.keyDown('right')
 elif Data == b'2\r\n':
 pyautogui.keyUp('right')
 pyautogui.keyDown('left')

• Gerben: You could try using a higher baudrate, instead of just 9600.
• Gerben: Possible explanation for the lag. Since serial data is being buffered; if you send data faster, than the serial connection can handle, you'd get lag. As the latest data has to wait in line to be send. Using a tiny delay, or better Serial.flush(), or Majenko's #3 suggestion would eliminate the lag caused by buffering.
• CrossRoads: NewPing right(9,6,100); NewPing left(7,5,100); Is the 100 the timeout for no return? Can you make that shorter?
• Samdare: its maximum distance ,100cm
• gre_gor: Don't edit the question and invalidate an existing answer.

Answer 1

A couple of things jump out at me:

1. You only need to run Serial.begin(9600) once in setup() - never in loop() like that.
2. Your delay(3000) will be causing a 3 second delay when R>L&&R-L>5.
3. You don't need to constantly send the data over and over again. You just need to send it once and once only when the state changes.

At the moment you're sending something like:

0000000000000000000000000000000000000000001111111111111111111111111111111111111111111111111111111111111111111111111111111111111100000000000000000000000000000000000000000000000000000000000000000002222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222200000000000000000000000000000000000000000000000000000000000000

when all you really need to do is send 01020. Remember what the state is and only send anything when that state changes from one iteration to the next. And never ever use delay().

• Gerben: The code is using Serial.println, so it's more like 0\r\n0\r\n1\r\n1\r\n. So three bytes, for every byte of actual data.
• Majenko: Yeah, but still it's overkill. And I didn't want to make my post 6 miles long to illustrate a point...