Problems sending data to my Arduino from Python using pySerial

Question

I'm trying to send a '1' or a '0' to my Arduino in Python using pySerial so that from my Arduino I can read whatever the Python program sends and then turn a relay on and off depending on what it reads from Python.

Here is the Python code:

import cv2
import imutils
import threading
import time
import serial
Arduino = serial.Serial("COM7")
Arduino.baudrate = 9600
cap = cv2.VideoCapture(0, cv2.CAP_DSHOW)
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 640)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 480)
_, start_frame = cap.read()
start_frame = imutils.resize(start_frame, width=500)
start_frame = cv2.cvtColor(start_frame, cv2.COLOR_BGR2GRAY)
start_frame = cv2.GaussianBlur(start_frame, (21, 21), 0)
alarm = False
alarmMode = False
alarmCounter = 0
def beep_alarm():
 global alarm
 for i in range(5):
 if not alarmMode:
 break
 print("HE MOVIN HE MOVIN")
 Arduino.write(str.encode("1"))
 alarm = False
 Arduino.write(str.encode("0"))
while True:
 _, frame = cap.read()
 frame = imutils.resize(frame, width=500)
 if alarmMode:
 frameBW = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
 frameBW = cv2.GaussianBlur(frameBW, (5, 5), 0)
 difference = cv2.absdiff(frameBW, start_frame)
 threshhold = cv2.threshold(difference, 25, 255, cv2.THRESH_BINARY)[1]
 start_frame = frameBW
 if threshhold.sum() > 300:
 alarmCounter += 1
 else:
 if alarmCounter > 0:
 alarmCounter -= 1
 cv2.imshow("Cam", threshhold)
 else:
 cv2.imshow("Cam", frame)
 if alarmCounter > 20:
 if not alarm:
 alarm = True
 threading.Thread(target=beep_alarm).start()
 keypress = cv2.waitKey(30)
 if keypress == ord("t"):
 alarmMode = not alarmMode
 alarmCounter = 0
 if keypress == ord("q"):
 alarmMode = False
 break
cap.release()
cv2.destroyAllWindows()

It's basically a movement detection program. If it detects me moving it should send a '1' to the Arduino where it then turns on a relay.

Here is the arduino code:

int relay = 11;
bool moving = false;
void setup() {
 Serial.begin(9600);
 Serial.setTimeout(1);
 pinMode(relay,OUTPUT);
 digitalWrite(relay, LOW);
}
void loop() {
 while (Serial.available()) {
 if (Serial.read() > 0) {
 while (!Serial.available()) {
 if (moving == false) {
 digitalWrite(relay, LOW);
 delay(100);
 moving = true;
 } else {
 digitalWrite(relay, HIGH);
 delay(100);
 moving = false;
 }
 }
 }
 digitalWrite(relay,LOW);
 delay(100);
 }
}

• jsotola: are you able to send data successfully using serial monitor?

Answer 1

You didn't specify, what the problem actually is, but I already see an error, that is probably the problem here.

You are sending the string "0" or the string "1" from python. This being a string - in contrast to a number in some binary format - means, that it is encoded as ASCII text. Have a look at an ASCII table, for example here. You will find the symbol/character "0" to have a decimal value (DEC) of 48. "1" is decimal 49.

On the Arduino side you have Serial.read() > 0. Serial.read() returns an integer, so a decimal number (or more specific a binary representation of it). So you got either 48 > 0 or 49 > 0, which is always true. Keep in mind the difference between ASCII encoding and binary integer encoding.

You can replace the above with

if(Serial.read() == '1'){

This tests, if you received the character (ASCII encoded!) '1' (the single quotes are for characters).

Note: It seems you want to switching the relay on and off until another character is send. Currently you are switching the relay 10 times a second. That is much for a relay, especially, if you are switching high voltages (like mains power). You should be aware, that this might cause problems with your relay after some time.