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Author Topic: Why not a voltage selector on the Arduino board?  (Read 1398 times)
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All I see is an outstanding reason to make a 5/3V3 board. It certainly isn't the cost and interfacing is not difficult. I figured it out in about 3 hours...

Bob
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Well the new Due board solved that, it's 3.3v only, slap on a 5 volt shield and it might ruin your day.

I realize this may be anathema to Atmel advocates, but I just bought a Digilent Chipkit uC32
board [Arduino-UNO form-factor], and it uses an 80-Mhz PIC32 chip that runs at 3.3V, but
all the digital I/O pins are 5V tolerant. My little Pololu Zumo robot wants speed, speed, and
more speed. [back to my cave now].

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I realize this may be anathema to Atmel advocates,

Well not to me, as I feel the Due should have been designed to be hardware compatible with all legacy shield boards, but was told (I think) that the 'desired market target price' for the Due would have been to high.

Lefty
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5V shield only ruins your day if you power it from 5V.
So power it from 3.3V instead and all is honky-dory.

Gives me an idea for a DUE shield. Bring all pins in, but only 3.3V for power. Any device must be 3.3V device.

2nd shield - Bring 5V in, but provide offset female headers that are all 3.3/5V buffered with TXB0108 chips or equivalent. Fully compatible with 5V shields, but only 3.3V is exchanged with the DUE.
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My home brew boards all have jumpers to select Vdd = 5V or 3.3V. I've been running 328's
at 3.3V and 16 Mhz fine for year now

That's your choice, but anecdotal tales of running parts outside their spec proves nothing. Going around telling people it's OK to do so isn't doing anybody a service.

Well, normally I'm a lot more conservative, but in this case, I say full speed ahead and
 d*mn the torpedoes. [It works until you're at the bottom of the sea].
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5V shield only ruins your day if you power it from 5V.
So power it from 3.3V instead and all is honky-dory.

Now we have the reverse problem to a short time ago. Previously, some vendors were selling
shields, like for XBee and SD cards, that did not have 5V-to-3.3V level-shifters on them, and
people were blowing up the XBees and SD Cards. So, the vendors finally came around to
redesigning the shields better.

So, maybe the shields should have the 5V vs 3.3V option, then the DUE is safe. Can of worms.
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5V shield only ruins your day if you power it from 5V.
So power it from 3.3V instead and all is honky-dory.

So any active components on any specific legacy 5 volt shield will run at 3.3vd? Also there is still 5vdc on the 5V shield pin even on a Due board, so any old 5 volt shield will still run at 5vdc just due (no pun) to the fact that it's mounted to a Due board.

Gives me an idea for a DUE shield. Bring all pins in, but only 3.3V for power. Any device must be 3.3V device.

Easy to design a shield for Due use only or for Uno use only, trying to get a shield compatible for both is what we are asking about.

2nd shield - Bring 5V in, but provide offset female headers that are all 3.3/5V buffered with TXB0108 chips or equivalent. Fully compatible with 5V shields, but only 3.3V is exchanged with the DUE.

Maybe, not familiar with that TSB0108 chip. Does it support the high output current that a 8 bit AVR output pin can supply?
Lefty
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"Maybe, not familiar with that TSB0108 chip. Does it support the high output current that a 8 bit AVR output pin can supply?"
TXB010x would be for logic level translation of control lines between Due IO and 5V devices on the shield.
http://www.ti.com/product/txb0101
Also available with 2,4,6,8 buffered lines:
txb0102
txb0104
txb0106
txb0108
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Arduino for Teens available at Amazon.com.

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