HELP: Transmit Data Over Laser and Recieve from LDR

[selimay]

As title say, I want to send data (i.e. text later .bmp file) from one Arduino to another by laser turn ON and OFF respectively HIGH and LOW and receive it from LDR.

I have to use Matlab as Sender and Python ( Visual Studio Code) as Receiver side.
So far, I have managed the task successfully when I use Matlab for both sides.

Video in Link : Short Video
In the video, there might be shown some other electronic components, but I deactivated all of them so I don't need them. The circuit is very simple:

Sender: Laser Module, S goes to Arduino Digital 3, GND to Arduino GND
Receiver: There is a resistor serial to LDR where LDR reader pin goes to Arduino Digital 3 Pin, GND-GND. That's all. Remaining components are irrelevant.

Sender Code:

a = arduino("COM5","Uno");
foku = fopen('test.txt','r');

if true

writeDigitalPin(a,'D3',1);


while ~feof(foku)
    byte_content = fread(foku, 1, 'uint8');
    if byte_content>-1
        b1 = bitget(byte_content, 1:8);  
        for j=1:1:8
            fprintf("%d",b1(j));
            writeDigitalPin(a,'D3',b1(j));
             pause(1/100);
        end       
    end
    
end
fclose(foku);
end

Reciever Code:

b = arduino("COM6","Uno");
fyaz = fopen("new123.txt","w");

if true
    
while readDigitalPin(b,'D3')~=1
    fprintf('waiting-');
end



for x=1:1:26
    dizi=(8);
    for j=1:1:8
        dizi(j)=readDigitalPin(b,'D3');
        fprintf('%d',dizi(j));  
        pause(1/100);   
    end

sayi=0;
for c=1:1:8
    sayi=sayi+(dizi(c)*power(2,c-1));
end
fwrite(fyaz,sayi,'uint8');
end
fclose(fyaz);
end

What I'm asking, I couldn't make it work when I use Python as receiver. It starts well for first 3-4 bytes and then I get wrong characters due to wrong bits pattern. As you all assume, at some point there is a synchronize problem sender and receiver.

Are they give same delay time, Matlab pause(1/100) function and Python time.sleep(1/100)?

Here is my draft code in Python:

import pyfirmata
import time

board = pyfirmata.Arduino('COM6')

f = open("demo.txt", "w")

f2 = open("demo2.txt", "w")

button = board.digital[3]
it = pyfirmata.util.Iterator(board)
it.start()

button.mode = pyfirmata.INPUT
time.sleep(3)

while button.read() != 1:
    
    print("waiting-")


for i in range(7):
    dizi = [0,0,0,0,0,0,0,0]
    for j in range(8):
     dizi[j] = board.digital[3].read()
     f2.write(str(int(dizi[j])))
     time.sleep(1/100) 
     
    
    sayi=0
    for c in range(8):
            sayi = sayi+(dizi[c]*int(pow(2,c-1)))
        
    
    print(str(sayi))
    f.write(chr(sayi))

f.close()
f2.close()

I'm going to record and upload a video for this code soon. So, you all may get know well where I'm missing something. I would be happy if you teach me better way to handle this task.
Thank you all for your interests.

[kolaha]

Hi. Do you have an oscilloscope to check if LDR is responsible enough?
And the temperature of LDR is good to checking while transmitting. under heat drift his resistance.

[lastchancename]

You don’t mention a bitrate in your code, but assuming you know what you’re doing, I’d strongly suggest you use a modulation scheme… e.g the. beam is driven at say 40khz+, and your data is used to gate that on/off. there are certainly more elaborate methods, but that would be a good starting point.

e.g. 3 cycles on == a 1 bit, 3 cycles off == a zero bit.

[StefanL38]

An LDR will be way too slow to react on 40 kHz. For something like this you need a fotodiode or a foto-transistor.

best regards Stefan

[lastchancename]

Good point… I was assuming a rethink from scratch with the appropriate technology!