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5v vs 3.3v


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#1 pascal06

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Posted 11 August 2010 - 09:03 PM

Hello, I use multiple shield with my Arduino, and before trying to plug any shield on my netduino, I would like to be sure that's not dangerous regarding TTL level : http://www.nuelectro...&products_id=20 http://www.nuelectro...&products_id=12 http://www.nuelectro...1&products_id=2 http://www.nuelectro...1&products_id=4 In general, what's happen if I plug a shield designed for Arduino (TTL 5v) to netduino ? Is it dangerous or it simply doesn't work ? Sorry for this basic electronic question, but I'm a software guy, need to stay humble with electronic, /pascal

#2 Chris Walker

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Posted 11 August 2010 - 09:15 PM

In general, what's happen if I plug a shield designed for Arduino (TTL 5v) to netduino ? Is it dangerous or it simply doesn't work ?


The Netduino's digital pins output 3.3V signals, but inputs from shields can be up to 5V. Analog pins in analog mode need to stay at <=3.3V.

Pretty much all of the Arduino shields should work electrically, with the following two exceptions:
1. If the shield provides 5V analog inputs, you'd need to modify it to provide 3.3V analog inputs instead.
2. If the shield requires 5V data signals, you'd need to put a level converter in between the Netduino and the shield.
3. Netduino has 4 hardware PWM (vs. 6 PWM on the Arduino's AVR chip). We may have "software PWM" in the future, but for now you might lose a small bit of functionality on certain motor control shields.

That's it. Netduino provides 5.0V and 3.3V power just like Arduino. Many/most shields should work. We're compiling a list and will put it on an upcoming Netduino "accessories" page.

Does that help?

Chris

#3 Chris Walker

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Posted 11 August 2010 - 09:27 PM

http://www.nuelectro...&products_id=20
http://www.nuelectro...&products_id=12
http://www.nuelectro...1&products_id=2
http://www.nuelectro...1&products_id=4


A few notes on 3.3V vs. 5V:
1. On LCDs, go for 3.3V LCDs.
2. Some shields with SD on board scale the signal down from 5V to 3.3V. Many work with 3.3V too (like the Adafruit ones) but some scale 3.3V down to something much lower--so check for 3.3V signal compatibility.
3. Generally, just ask the retailer/manufacturer if their device is compatible with 3.3V signals.
4. I2C signals are driven by forcing the signal to 0V, so there is no 3.3V vs. 5V issue there.

Drivers are going to be required for some shields. We're working on some. Community members are working on some. Together we'll make lots of projects possible.

Chris

#4 pascal06

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Posted 11 August 2010 - 09:37 PM

The Netduino's digital pins output 3.3V signals, but inputs from shields can be up to 5V. Analog pins in analog mode need to stay at <=3.3V.

Pretty much all of the Arduino shields should work electrically, with the following two exceptions:
1. If the shield provides 5V analog inputs, you'd need to modify it to provide 3.3V analog inputs instead.
2. If the shield requires 5V data signals, you'd need to put a level converter in between the Netduino and the shield.
3. Netduino has 4 hardware PWM (vs. 6 PWM on the Arduino's AVR chip). We may have "software PWM" in the future, but for now you might lose a small bit of functionality on certain motor control shields.

That's it. Netduino provides 5.0V and 3.3V power just like Arduino. Many/most shields should work. We're compiling a list and will put it on an upcoming Netduino "accessories" page.

Does that help?

Chris


Many thanks Chris,


In conclusion, only analog input is risky. But is it realy dangerous for netduino or not ?

/pascal

#5 Chris Walker

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Posted 11 August 2010 - 10:01 PM

In conclusion, only analog input is risky. But is it realy dangerous for netduino or not ?


I have tested Netduinos with 5V analog inputs to see what happened. The analogInput.Read() values were of course meaningless due to the overvoltage.

While I could never see any physical damage, the official Atmel datasheet says not to subject the analog inputs (in analog mode) to more than 3.3V.

So officially, don't do it. It would technically void your warranty.

That said, 5V is fine on all the digital pins (and is fine on the analog pins when they're used in digital mode). Since the analog pins act as digital pins by default, you can also just not use analog inputs that are 5V--no damage worries there. [Just make sure nothing is feeding 5V to the AREF line.]

Chris




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