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Topic: Why not a voltage selector on the Arduino board? (Read 1 time) previous topic - next topic

giantsfan3

Dec 08, 2012, 01:07 am Last Edit: Dec 08, 2012, 01:10 am by giantsfan3 Reason: 1
It seems that the majority of sensors and peripheral ICs available out there nowadays run on 3.3V (as opposed to 5V). Nevertheless, I understand that in order to maintain compatibility with already existent shields, the Arduino board has to continue to be maintained at 5V operation.

But what are some reasons they haven't implemented at least a 3.3V / 5V selector SWITCH on the Arduino board (even newer revisions of the same don't have this), so that users can choose based on their needs -- are there any possible difficulties or disadvantages to this?

Seems to me that this would just require adding a cheap LDO regulator into the circuit with 3.3V output that is selected based on the switch. And voila, you would now have the microcontroller compatible with 3.3V level signals of your peripheral circuitry, or even 3.3V-level shields.

And pretty much the only disadvantage to having such a voltage selector, as far as I can see, is that beginners may mistakenly leave it on 3.3V and use a 5V shield.

Apart from that, for most cases, such a switch would only add a lot of versatility, I think.

retrolefty

Quote
But what are some reasons they haven't implemented a 3.3V / 5V selection switch on the Arduino board (even newer revisions of the same don't have this) -- are there any possible difficulties or disadvantages to this?


Well one issue with that is that Atmel does not rate their 328p chips as able to run reliably at 16Mhz at the 3.3vdc Vcc voltage. Many people have run their chips at 16Mhz with 3.3vdc Vcc without problems, but that is indeed working outside the datasheet specifications for the device, effectively 'overclocking' when running at that speed and Vcc voltage. The Seeeduino 328p 'arduino clone' board does use a small selector switch to operate the board at either 5vdc or 3.3vdc.

Lefty


giantsfan3

@retrolefty:
Looking at the datasheet graph, I see that is indeed the case (although 12 Mhz might be an option).

Have you used the Seeeduino's selector capability -- I'm curious how that feature has worked out for you in general.

Looking at their schematic (http://www.seeedstudio.com/wiki/images/7/7b/Seeeduino_v3.0.pdf), they are using the selector to switch a LD1117-3.3 regulator after the 5V. Seems a fairly straightforward approach.

retrolefty


@retrolefty:
Looking at the datasheet graph, I see that is indeed the case (although 12 Mhz might be an option).

Have you used the Seeeduino's selector capability -- I'm curious how that feature has worked out for you in general.

Well I don't actually own a 328p based Seeeduino board, so I can't report on it first hand.

Looking at their schematic (http://www.seeedstudio.com/wiki/images/7/7b/Seeeduino_v3.0.pdf), they are using the selector to switch a LD1117-3.3 regulator after the 5V. Seems a fairly straightforward approach.

Yes, and as I said there have been several people over the years run their 'standalone' 328p projects at 3.3v and 16mhz and reported no problems, so I suspect it mostly a case of Atmel using conservative specification that has to take in worst case temperature ratings and such. I suspect it would work fine for you. It's not like the board will burst into fire and burn your house down.  ;)
Lefty


Henry_Best



And pretty much the only disadvantage to having such a voltage selector, as far as I can see, is that beginners may mistakenly leave it on 3.3V and use a 5V shield.



Worse would be using a 3.3V sheild with the voltage kept at 5V. It tends to let the 'magic smoke' out.

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