ATmega328P on 8Mhz internal clock, serial comm, and libraries question

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1

I'm reading that using the internal 8Mhz oscillator allows you to run the arduino with a bare chip, which would be GREAT for my purpose. However, i would like to run serial at 115200bps. after reading this as reference, http://www.wormfood.net/avrbaudcalc.php, it is telling me that i can't reach that target baud due to incompatible bit rate with 7% error. I just wanted to know if anyone had experiences where that as wrong. Also, has anyone successfully gotten serial communication to work on the internal oscillator.

Also, for the libraries that have been made, do i have to alter them in any way to get it working from 16Mhz default on the Uno to 8Mhz on the internal? Will they work out of the box, like Servo.h or will that also require additional tweaking?

Thank you!

2

Standard libraries will work fine at 8 MHz.

3

Thanks man! Any word on the serial stuff?

4

Can you use a baud rate with zero error? Like 125K?

The processor leaves the factory with the internal oscillator calibrated to ±10%. It is possible to tune the oscillator to ±1%. In addition to dealing with the baud rate error you may have to tune the oscillator.

You could tune the oscillator to run a bit slow and get closer to 115200 baud rate. Unfortunately everything else (millis, delay) will also run a bit slow.

5

Note: That's ±10% at Vcc=3V and temperature=25°C. The frequency will change with voltage and temperature. At 3V the nominal frequency goes from under 7.7 MHz at -40°C to 8.2 MHz at 85°C. At 5V the frequency is roughly 100 KHz higher (8.1 MHz at 25°C).