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Arduino takes 1-2 seconds to process serial input, how can I speed this up?

I am almost entirely new to arduino/C++ so forgive me if this seems stupid. I am using a python program that detects faces in the camera frame and sends the x and y coordinate of the face to the arduino via serial (I have not implemented any code to deal with y yet). This works so long as I limit how often it sends the coordinates, however if they are sent too fast, the arduino seems to simply stop responding. My hypothesis as to why is that it is not able to read the data fast enough and it is lost before it can be processed. I know ultimately 1-2 seconds is not that big of a deal but unfortunately for me I'm a bit of a perfectionist and a 1-2 second delay really gets on my nerves.
As for the python script:
while True:
# Facial recognition stuff here
for (x, y, w, h) in faces:
cv2.rectangle(frame, (x, y), (x+w, y+h), (0, 255, 0), 2)
print(x, y)
if i == 30:
coord = f'{x} {y}'
arduinoData.write(coord.encode())
i = 0
i += 1
and the code running on my arduino:
#include <Servo.h>
Servo myservo;
int gLED = 2;
int rLED = 3;
String words[2];
void setup() {
Serial.begin(115200);
pinMode(rLED, OUTPUT);
pinMode(gLED, OUTPUT);
myservo.attach(8);
myservo.writeMicroseconds(1450);
}
void loop() {
while (Serial.available() > 0) {
String input = Serial.readStringUntil('\r');
int spaceIndex = input.indexOf(' ');
if (spaceIndex != -1) {
words[0] = input.substring(0, spaceIndex);
words[1] = input.substring(spaceIndex + 1);
} else {
words[0] = input;
words[1] = "";
}
int pos1 = words[0].toInt();
if (pos1 > 300) {
digitalWrite(gLED, HIGH);
digitalWrite(rLED, LOW);
myservo.writeMicroseconds(1400);
}
if (pos1 < 240) {
digitalWrite(rLED, HIGH);
digitalWrite(gLED, LOW);
myservo.writeMicroseconds(1510);
}
if (pos1 >= 240 && pos1 <= 300) {
digitalWrite(gLED, LOW);
digitalWrite(rLED, LOW);
myservo.writeMicroseconds(1450);
}
}
}
Does anyone have any tips on how I can speed up the response? Is it slow because of something stupid that I'm doing or is there maybe a different protocol that is faster? I briefly looked into i2c but I'm not sure if it's a better option.

#Roman is true. May be better to monitor the serial at regular interval and get data as they arrive:
unsigned long timer;
void loop() {
if (millis() - timer > 200) { //tick every 200mS
timer=millis();
String input = serialListen();
// etc.....
}
}
String serialListen() {
String SerMsg = "";
while (Serial.available()) {
// get the new byte:
char inChar = (char)Serial.read();
if (inChar == '\n') { //end char
return SerMsg;
} else {
// add it to the inputString:
SerMsg += inChar;
}
}
}

How to send a decimal number from python to arduino

i am trying to send a decimal number from python to arduino, the problems is data is sent in an other type (i don't know which one maybe binary), so i did not get the desired response!
here is my arduino code
void setup() {
// put your setup code here, to run once:
pinMode(10, OUTPUT);
Serial.begin(9600);
}
void loop() {
// put your main code here, to run repeatedly:
if (Serial.available() > 0) {
char k = Serial.read();
if (k > 500) {
analogWrite(10, 255);
delay(1000);
}
if (150 < k < 500) {
analogWrite(10, 128);
}
else if (k < 150) {
analogWrite(10, 0);
delay(1000);
}
Serial.print(k);
}
}
& here is python code
import serial
import struct
arduinoData = serial.Serial('com3',9600)
data = 0
while(1==1):
serialcmd = input("serial command: ")
arduinoData.write (struct.pack('>B',serialcmd))
data = arduinoData.readline()
print(data)

calling serial.read from other function

I'm trying to connect python with Arduino code using serial but I cannot call serial.read() within the led_on_off() function.
This is the Arduino code:
int led=13;
int val=0;
char functionname='K';
#include <string.h>
void setup()
{
Serial.begin(9600);
pinMode(led, OUTPUT);
digitalWrite (led, LOW);
Serial.println("Connection established...");
}
void loop()
{
functionname = Serial.read();
if (functionname= 'L')
{
led_on_off();
}
}//void loop
void led_on_off()
{
val=Serial.read()
if (val= 1)
digitalWrite(led,HIGH)
else if (val == 0)
digitalWrite(led,LOW)
}
And this is the python code:
import serial
Arduino_Serial = serial.Serial('com18',9600) # Create Serial port object called arduinoSerialData
print(Arduino_Serial.readline()) # read the serial data and print it as line
print("Enter L to ON LED and M dc motor")
input_data = input()
Arduino_Serial.write(input_data.encode())
print(Arduino_Serial.readline())
input_value=input("enter 1 or 0")
Arduino_Serial.write(input_value.encode())
my expectation is to get input (1 or 0) from python code and process it within the led_on_off function in Arduino code using the serial.read() function and turn on or off the led at pin 13.

As already stated by #KIIV your Arduino code has some syntax errors. Besides that, you are sending a string from your Python script (input function) so you need to read it as a string on Arduino. Something like this would do the job:
Python script:
import serial
# Create Serial port object called arduinoSerialData
Arduino_Serial = serial.Serial('com18', 9600)
# read the serial data and print it as line
print(Arduino_Serial.readline())
input_data = input("Enter L to ON LED and M dc motor: ")
Arduino_Serial.write(input_data.encode())
print("Received Command:", Arduino_Serial.readline())
while True:
input_value = input("enter 1 or 0")
Arduino_Serial.write(input_value.encode())
Arduino code:
int led = 13;
void setup()
{
Serial.begin(9600);
pinMode(led, OUTPUT);
digitalWrite(led, LOW);
}
void loop()
{
//void loop
if (Serial.available())
{
String functionname = Serial.readString();
if (functionname == "L")
{
Serial.println("Command received from Arduino!");
while (1)
{
led_on_off();
}
}
}
}
void led_on_off()
{
if (Serial.available())
{
String val = Serial.readString();
if (val == "1")
digitalWrite(led, HIGH);
else if (val == "0")
digitalWrite(led, LOW);
}
}

Stepper motor connected with arduino is not listening to the initial state send by python

I'm sending data from a python script to my Arduino board. I can succesfully communicate with the board. Based on the data send by the python, the stepper motor connected should either move forward or backward. If python is sending '0' the motor should rotate forward and if python is sending '1' then the motor should rotate backward. When i type '0' in the serial monitor the stepper moves forward and on '1' stepper moves backward. But when python is sending data at first, stepper is not moving forward or backward. Only when the state change happens(if state changes from '1' to '0' or '0' to '1'), the stepper either moves forward or backward. I tried to see if data is send from python, the arduino is receiving data from python. Suggestion will be heavily appreciated.
Ardunio code
static const int SELENOID_PIN = 2;
static const int OPEN = '0';
static const int CLOSE = '1';
static const int STEPS = 30;
static const int delaylegnth = 10;
void setup() {
//establish motor direction toggle pins
pinMode(12, OUTPUT); //CH A -- HIGH = forwards and LOW = backwards???
pinMode(13, OUTPUT); //CH B -- HIGH = forwards and LOW = backwards???
//establish motor brake pins
pinMode(9, OUTPUT); //brake (disable) CH A
pinMode(8, OUTPUT); //brake (disable) CH B
Serial.begin(9600);
while(!Serial){}//wait until the serial port is connected
Serial.write('1');
pinMode(SELENOID_PIN ,OUTPUT);
}
void polarisingA()
{
digitalWrite(9, LOW); //ENABLE CH A
digitalWrite(8, HIGH); //DISABLE CH B
digitalWrite(12, HIGH); //Sets direction of CH A
analogWrite(3, 255); //Moves CH A
delay(delaylegnth);
}
void polarisingB()
{
digitalWrite(9, HIGH); //DISABLE CH A
digitalWrite(8, LOW); //ENABLE CH B
digitalWrite(13, HIGH); //Sets direction of CH B
analogWrite(11, 255); //Moves CH B
delay(delaylegnth);
}
void polarisingC()
{
digitalWrite(9, LOW); //ENABLE CH A
digitalWrite(8, HIGH); //DISABLE CH B
digitalWrite(12, LOW); //Sets direction of CH A
analogWrite(3, 255); //Moves CH A
delay(delaylegnth);
}
void polarisingD()
{
digitalWrite(9, HIGH); //DISABLE CH A
digitalWrite(8, LOW); //ENABLE CH B
digitalWrite(13, LOW); //Sets direction of CH B
analogWrite(11, 255); //Moves CH B
delay(delaylegnth);
}
void stepRight()
{
polarisingA();
polarisingB();
polarisingC();
polarisingD();
}
void stepLeft();
{
polarisingD();
polarisingC();
polarisingB();
polarisingA();
}
void spin(bool dir,int tickes)
{
//Serial.print(dir);
for(int i =0 ; i < tickes; i++)
{
if(dir == true)//right
{
stepRight();
}
else
{
stepLeft();
}
}
}
void loop() {
if(Serial.available() > 0)
{//there is incoming data form the serial and serial is setted up
handleData();
}
delay(5);
}
void handleData()
{
unsigned char a = Serial.read();
Serial.write("new data");
int action = -1;
if(a == OPEN)
{
action = 1;
}
else if(a == CLOSE)
{
//Serial.print("close");
action = 0;
}
if (action != -1)
{
bool dir = action == 1 ? HIGH : LOW ;
spin(dir,STEPS);
digitalWrite(SELENOID_PIN ,action ? HIGH : LOW );
Serial.write(a);//ack
}
}
Python code(Part only sending data to arduino):
def openthedoor(set_accepted_list,set_list_ant_id,set_forbidden_list,set_accepted_list_frozen):
if(((len(set_accepted_list)) >0) & (set_forbidden_list == set()) & ((set_accepted_list_frozen == None) or ((set_accepted_list_frozen & set_accepted_list)== set_accepted_list))):
print"yes,open the gate"
use_step(1)
else:
print"no,close the gate"
use_step(0)
def establishing_connection():
#serial.Serial("COM1",9600)
print ser.read();
last_action = -1
def use_door(activate):
global last_action
#global serial
if(last_action != activate):
send_data(activate)
last_action = activate
def send_data(data):
global ser
try:
if(ser == None):
ser = serial.Serial("COM1",9600,timeout = 0)
print "reconnect"
if(data==0):
ser.write('0')
print "python is telling the arduino to move stepper forward"
else:
ser.write('1')
print "python is telling the ardunio to move stepper backward"
time.sleep(0)
except IOError:
time.sleep(0)
ser.close()
#continue
ser = None
print "after read"

ArduinoPI Python - SERIAL CONNECTION LOST DATA

Intent: Control arduino uno from serial port
Tools:
https://github.com/JanStevens/ArduinoPi-Python
I got the server working on both my mac and my Model b+ Raspberry.
The browser behaves as shown in the picture below in both situations.
To me it looks like the server sent the message to Arduino successfully. But the data somehow gets lost on the way. The Arduino board resets every time I access the url in my browser. I googled and found that a 10uF capacitor between ground and reset pins would prevent the reset from happening. It did, but pin 3 won't go "HIGH". I got a LED+RESISTOR plugged on pin 3 and ground accordingly. I can see the Rx led blinking every time I access the url. So it makes me think that the Arduino is misunderstanding the command from my Flask sever.
OG Arduino code:
String cmd;
bool cmdRec = false;
void setup()
{
//Start the connection with the Raspberry Pi
Serial1.begin(115200);
// Start the connection with the Laptop, for debugging only!
//Serial.begin(115200);
}
void loop()
{
handleCmd();
}
void serialEvent1() {
while(Serial1.available() > 0) {
char inByte = (char)Serial1.read();
if(inByte == ':') {
cmdRec = true;
return;
} else if(inByte == '#') {
cmd = "";
cmdRec = false;
return;
} else {
cmd += inByte;
return;
}
}
}
void handleCmd() {
if(!cmdRec) return;
// If you have problems try changing this value,
// my MEGA2560 has a lot of space
int data[80];
int numArgs = 0;
int beginIdx = 0;
int idx = cmd.indexOf(",");
String arg;
char charBuffer[20];
while (idx != -1) {
arg = cmd.substring(beginIdx, idx);
arg.toCharArray(charBuffer, 16);
data[numArgs++] = atoi(charBuffer);
beginIdx = idx + 1;
idx = cmd.indexOf(",", beginIdx);
}
// And also fetch the last command
arg = cmd.substring(beginIdx);
arg.toCharArray(charBuffer, 16);
data[numArgs++] = atoi(charBuffer);
// Now execute the command
execCmd(data);
cmdRec = false;
}
// For advanced function like switch all the leds in RGB
void execCmd(int* data) {
switch(data[0]) {
case 101:
{
for(int i = 2; i < (data[1]*2)+1; i+=2) {
pinMode(data[i], OUTPUT);
analogWrite(data[i], data[i+1]);
}
}
break;
case 102:
{
pinMode(data[1], INPUT);
int sensor = analogRead(data[1]);
Serial1.println(sensor);
}
break;
case 103:
{
String result = "";
int sensor = 0;
for(int j = 2; j < data[1]+2; j++) {
pinMode(data[j], INPUT);
sensor = analogRead(data[j]);
result += String(sensor)+",";
}
Serial1.println(result);
}
break;
default:
{
pinMode(data[0], OUTPUT);
analogWrite(data[0], data[1]);
}
break;
}
}
It does not compile this way. So I uncommented the second Serial.begin line and deleted all the "Serial1." appearances on the code. I can't see no action on the arduino IDE serial when I test it on my mac.

As the code was written with an Arduino Mega that got 2 or 3 serial ports, void serialevent1() is triggered when there is communication going on the the MEGA's SERIAL1 port. Since I am working on the UNO, that only have 1 serial port, all i had to do was delete the "1" before the parenthesis and all worked as supposed.
void serialEvent() { }