#ARDUINO NANO SCHEMATIC CRYSTAL OR RESONATOR SOFTWARE#
Granted, this is all through the eyes of a hardware engineer, so there may be specific software considerations that are preventing this from being possible, but to me, this seems the obvious solution.įinally, I have attached the modified board (I tried to make as little changes as possible to the rest of the board, although I had to shift around a few traces, it still passes the DRC file I commonly use). The end-user would still have the option of cutting the trace and installing a different frequency crystal or resonator to their liking, but this change saves on the part count and provides a much more accurate default clock source for the microcontroller. So all that is needed is to set the corresponding fuses on both devices, and route a trace from the ATmega8U to the ATmega328P. The ATmega8U (as well as most AVR microcontrollers) have a clock output fuse which can output a buffered version of the input clock on one of the pins, in this case, PC7. Thankfully, the fix (to my knowledge) seems fairly simple. For the resonator, however, such a clock would be off by 3 hours and 3 minutes by the end of the month. The crystal oscillator has a stable frequency of 16.0000MHz (as well as my Rigol scope's frequency counter can tell) and a jitter of about 4ns for the same conditions.Īssuming a +/-30ppm frequency tolerance for the crystal, a clock based on such a crystal would be accurate to within about 1 minute and 19 seconds per month. Here is a comparison between the 16MHz resonator and 16MHz crystal on the Arduino Uno:Īs you can see, the resonator has a stable frequency of 15.9331MHz, a -0.42% difference, as well as a jitter of about 7ns over a 30s period, 1ms from the trigger. Typically crystal oscillators are selected for a good balance between accuracy and cost.
I would like to suggest that the 16MHz ceramic resonator used to clock the ATmega328P be removed, and replaced with a cuttable solder jumper to the ATmega8U's CLK0 (Clock Output) pin.įor precise timing, such as running real time clocks and waveform generation applications, it is desirable to use a clock reference with the highest available accuracy. Looking around, I couldnt find a resonator that had the accuracy I wanted (30ppm or less hopefully), so a crystal oscillator (xtal) was the right solution. Hi all, I'm a third year EE student at Cal Poly San Luis Obispo, and I've owned an Arduino Uno for a few months now, and I've got a suggestion for the next revision, with some evidence to support it.
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