Is it possible to control/read Arduino pins at different frequencies?

Hello,

The attached code is meant to flash an RGB LED and record data from a photoresistor. Currently, the code flashes the LED on one line, and then records data from the analog chanel on the next line. Ideally, I would like to have parallel code that flashes the LEDs based on a specific duty cycle (e.g. 6 Hz flashes cycling red, green, and blue) but a higher sampling frequency for the photoresistor analog chanel (e.g. 30 Hz). Is this possible within MATLAB's paradigm of sequential code execution?

Thanks in advance.

%% Arduino RGB LED Control%%
clear all
clc

% Create an arduino object
a = arduino();   

% Collection parameters
cycles = 10;
flashTime = .1;
pauseTime = .1;
photoResistor = zeros(cycles,3);

% Configure and pulse LED based on collection parameters
writePWMVoltage(a,'D3',5); % Red
writePWMVoltage(a,'D5',5); % Green
writePWMVoltage(a,'D6',5); % Blue

for i = 1:cycles
pause(pauseTime);
%Flash Red
writePWMVoltage(a,'D3',0); % Red
writePWMVoltage(a,'D5',5); % Green
writePWMVoltage(a,'D6',5); % Blue
pause(flashTime); photoResistor(i,1) = readVoltage(a, 'A0'); 
writePWMVoltage(a,'D3',5); % Red
pause(pauseTime)

writePWMVoltage(a,'D3',5); % Red
writePWMVoltage(a,'D5',0); % Green
writePWMVoltage(a,'D6',5); %Blue
pause(flashTime); photoResistor(i,2) = readVoltage(a, 'A0'); 
writePWMVoltage(a,'D5',5); % Green
pause(pauseTime)

writePWMVoltage(a,'D3',5); % Red
writePWMVoltage(a,'D5',5); % Green
writePWMVoltage(a,'D6',0); %Blue
pause(flashTime); photoResistor(i,3) = readVoltage(a, 'A0'); 
writePWMVoltage(a,'D6',5); % Blue
pause(pauseTime);


plot(photoResistor(:,1),'r');hold on;
plot(photoResistor(:,2),'g');hold on
plot(photoResistor(:,3),'b');
legend('Red', 'Green', 'Blue');hold off;


end

writePWMVoltage(a,'D3',5); % Red
writePWMVoltage(a,'D5',5); % Green
writePWMVoltage(a,'D6',5); %Blue


clear a %Disconnect from Arduino

Answer 1

[Amrtanshu Raj]

Hi,

Parallel computation or multithreading is not supported by Arduino so flashing the LED and reading the Photo Resistor at different frequency would not be possible.

However I can think of a work around, if you try to implement the logic such that

1. Have a main loop without any delays.
2. Read the photoresistor at every loop.
3. Store the time stamp every time the led was switched/changed in a variable.
4. Switch/toggle the led when the (current time - last time > threshold).

This is obviously not multi threading but since the execution frequency is high enough, it can be considered almost parallel for practical purpose.

Hope this helps !!