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Author Topic: What happens exactly when I feed a 5V Pro Mini with 3.3V ?  (Read 203 times)
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Hello,

I have been using a Sparkfun 3.3V FTDI basic breakout board to connect and feed a Pro Mini 5V / 16 MHz clone (Wattuino) because I thought it was a 5V FTDI. To my surprise it seems the Arduino is running fine. But I would like to know what is happening in the board. Is the processor running at 8 MHz instead of 16 MHz automatically ? Other consequence ?

Thank you in advance.
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The basic clock speed is set by hardware, i.e. the crystal or resonator in the circuit, so changing supply voltage does not change that*. Basically, nothing is happening, it's just running as usual. Technically it's being overclocked, since the minimum voltage for 16MHz operation is about 3.8V per the datasheet. But, as many have observed, the MCU will likely run fine this way under normal conditions (room temperature, etc.). Well-designed and well-engineered parts will have a safety margin which will typically allow operation outside of the stated specifications. No other consequences, but also no guarantee of proper operation, so if it doesn't run correctly (instructions could be incorrectly executed, etc.) then complaining to Atmel will likely not help smiley-grin

*Neither does changing the board in the Arduino IDE.
« Last Edit: February 10, 2013, 07:48:03 am by Jack Christensen » Logged

MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

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Good to know. Thanks!
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