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Topic: read ppm unknown voltage (Read 1 time) previous topic - next topic

gorgonas

Jun 01, 2013, 01:11 pm Last Edit: Jun 01, 2013, 01:31 pm by gorgonas Reason: 1
can I read a sign ppm (rc receptor) which voltage i dont know in one arduino due pin or that may damage the pin?

Thanks.

NielsJL

The most significant part of your question is "voltage I do not know"! I'd suggest you never plug anything directly into any Arduino pin, unless you are absolutely sure you know exactly what it is.

I have been working on reading and generating PPM signals for the last two weeks using the Uno -- my Due is on order. But even with the Uno I have been protecting the pin by having the PPM signal going through a voltage comparator (LM339). This has allowed me to read the PPM signal from my Spektrum DX6i's trainer port. I plan to use the same setup with the Due when it arrives as the LM339 can be powered by 3.3V.

You could use a simple transistor circuit to protect the Due's input pin, but definitely use something to protect it.

gorgonas


The most significant part of your question is "voltage I do not know"! I'd suggest you never plug anything directly into any Arduino pin, unless you are absolutely sure you know exactly what it is.

I have been working on reading and generating PPM signals for the last two weeks using the Uno -- my Due is on order. But even with the Uno I have been protecting the pin by having the PPM signal going through a voltage comparator (LM339). This has allowed me to read the PPM signal from my Spektrum DX6i's trainer port. I plan to use the same setup with the Due when it arrives as the LM339 can be powered by 3.3V.

You could use a simple transistor circuit to protect the Due's input pin, but definitely use something to protect it.


When I say I do not know the voltage I mean if they are not 3.3 v or 5v. i Should change the question then and ask.

Can a sign ppm 5v damage the arduino due pin?

anyway i use something to protect it. thanks.

NielsJL

#3
Jun 02, 2013, 08:12 pm Last Edit: Jun 02, 2013, 08:31 pm by NielsJL Reason: 1

Can a sign ppm 5v damage the arduino due pin?


The safest option is to ALWAYS assume the answer is yes!  ;)

I would never attach 5V to an 3.3V Due, just as I would never attach 7.6V to an Uno. My understanding is that Uno's internally have 1mA clamp diodes on their pins tied to the power rail and ground pins which will offer some protection, but not much. I don't know if this is true for all Atmel microcontrollers including the Due -- does any else reading this know if this is true?

[Edit: Even the Arduino site says it is a bad idea http://arduino.cc/en/Main/ArduinoBoardDue with the line "Warning: Unlike other Arduino boards, the Arduino Due board runs at 3.3V. The maximum voltage that the I/O pins can tolerate is 3.3V. Providing higher voltages, like 5V to an I/O pin could damage the board." ;)


anyway i use something to protect it. thanks.


I applaud your decision...it is the wisest choice.  :)

gorgonas

I know that a sign 5v would harm one pin in arduino due, my question is whether to be a ppm pulse train at 5v it would harm ...

A 5v pwm signal with a period of 20ms and 50% duty cycle behaves as an analog signal 2.5 v ... from there my doubt whether a PPM or PWM 5v signal ... really would harm pin or not.

thanks.

NielsJL

#5
Jun 03, 2013, 01:52 am Last Edit: Jun 03, 2013, 01:56 am by NielsJL Reason: 1

A 5v pwm signal with a period of 20ms and 50% duty cycle behaves as an analog signal 2.5 v ... from there my doubt whether a PPM or PWM 5v signal ... really would harm pin or not.


The concept you are describing, the DC equivalent voltage of an AC signal, applies to driving DC motors. I have used this myself both in class and at home. But, I would not apply it to anything else. Consider any voltage, AC or DC, over 3.3V applied to a Due pin as bad! It just isn't worth the (expensive) gamble. ;)

Edit: BTW, I'm happy to share code and schematics for the PPM generator and decoder sketches...well, once I get them ported to the Due from the Uno. If this will help you?

gorgonas



A 5v pwm signal with a period of 20ms and 50% duty cycle behaves as an analog signal 2.5 v ... from there my doubt whether a PPM or PWM 5v signal ... really would harm pin or not.


The concept you are describing, the DC equivalent voltage of an AC signal, applies to driving DC motors. I have used this myself both in class and at home. But, I would not apply it to anything else. Consider any voltage, AC or DC, over 3.3V applied to a Due pin as bad! It just isn't worth the (expensive) gamble. ;)

Edit: BTW, I'm happy to share code and schematics for the PPM generator and decoder sketches...well, once I get them ported to the Due from the Uno. If this will help you?


Yes, of course this will help me, thanks.

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