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Topic: 3.3V vs 5V boards (Read 909 times) previous topic - next topic

tim7

Hello everybody, I'm new to the Arduino community, after finding PIC too cumbersome for non-professional use.  Right now I have an Uno board and am extremely pleased with it.  For embedding in projects the Pro-Mini looks more suitable, but I'm a little uncertain about the programming requirements of the smaller board.

The Pro-Mini board comes in 3.3V and 5V versions, and appear to differ only in clock-rate and the voltage-regulator.  Likewise the recommended FTDI interfaces come in 3.3V and 5V flavours.

Now, do the voltages of the Arduino board and the FDTI interface need to match?  I understand that the "5V" board is clocked at 16MHz and therefore mightn't run properly when powered by a 3.3V interface.  But is there anything wrong with programming a "3.3V" board with a 5V interface?

retrolefty

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Now, do the voltages of the Arduino board and the FDTI interface need to match?  I understand that the "5V" board is clocked at 16MHz and therefore mightn't run properly when powered by a 3.3V interface.  But is there anything wrong with programming a "3.3V" board with a 5V interface?


I think the opposite is true. A 3.3v serial converter module/cable/chip should work fine with any arduino 5vdc board, as 3.3vdc is still a 'legal' logic HIGH voltage on a 5volt board.

However using a 5vdc converter module/cable/chip should not be used with a arduino 3.3vdc board as the higher voltage can damage the input pins on the 3.3vdc board.

Make sense?

Lefty


tim7

Isn't it the same ATmega168 chip on both 3.3V and 5V boards?  The chip spec says it can run at 1.8 to 5.5V, although it needs lower clock speeds at lower voltages.  So if I apply 5V to the Vcc pin of a 3.3V Pro-Mini board, it should be ok?

retrolefty


Isn't it the same ATmega168 chip on both 3.3V and 5V boards?  The chip spec says it can run at 1.8 to 5.5V, although it needs lower clock speeds at lower voltages.  So if I apply 5V to the Vcc pin of a 3.3V Pro-Mini board, it should be ok?


I think so. The key thing is you can't apply a voltage to a input pin that is higher then the voltage powering the chip.

Lefty


tim7

Right-ho.  I've convinced myself that the only potential problem is peripheral devices connected to the 3.3V Arduino which might be intolerant of 5V coming from the FTDI interface.  But in any case the 3.3V FTDI interface cannot supply much current, so peripherals should be disconnected anyway during programming.

So I shall try it and report back here.  And if it doesn't work, it appears that the FTDI interfaces can easily be altered from 5V to 3.3V.

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