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

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Michael McGeehan
Michael McGeehan 2021-1-27
回答： Amrtanshu Raj 2021-4-23
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

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Amrtanshu Raj
Amrtanshu Raj 2021-4-23
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 !!

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