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readVoltage() reading only 0 or 5

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Gun Min Song
Gun Min Song on 7 Nov 2018
Answered: Rohan Kale on 14 Feb 2020
From an Arduino Mega I am outputting 0,1,2,3,4 volts using writePWMVoltage function (at D13), then I connected D13 to A0 for readVoltage. In theory, I am supposed to get 0,1,2,3,4V from A0, but I am only getting values 0 or 5 from A0. I already checked D13 is outputting correct values by measuring with DMM.
Am I wiring something wrong? Why is this happening? Any help is appreciated :)

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Gun Min Song
Gun Min Song on 7 Nov 2018
This is the code I used for this experiment ----------------------------------------------
clear
clc
a = arduino
for i=0:4
writePWMVoltage(a,'D13',i)
voltage(i+1) = readVoltage(a,'A0')
pause
end
writePWMVoltage(a,'D13',0)
voltage(6) = readVoltage(a,'A0')
Walter Roberson
Walter Roberson on 8 Nov 2018
https://www.mathworks.com/help/supportpkg/arduinoio/ref/writepwmdutycycle.html
Try setting the duty cycle higher in case it is returning to base before you can read it.

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Answers (1)

Rohan Kale
Rohan Kale on 14 Feb 2020
In my understanding you are trying to read the DC voltages from the PWM waveforms generated on D13. Your code sequence seems to be alright. However, the hardware setup is where the problem is originating. In theory, the DC i.e. mean voltage, can be changed by changing the PWM duty cycle. I think the readVoltage API is just picking up the instances where the waveform is either a LOW or a HIGH, that's why you are reading either 0V or 5V. In order to read DC voltages correctly from the waveform, you may want to insert an RC filter between the PWM and analog pins. The RC filter will essentially increase the decay time as the capacitor would now discharge slowly. Try varying time constant of the circuit, may be keep it as 0.1 seconds. This should probably solve your issue.

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