manitou
Senior Member+
Paul notes that teensy 3.0 uses 16mhz crystal with 15ppm accuracy. I've used an NTP-host to periodically query an MCU's millis() to check frequency of the crystal. My teensy crystal was within -5 ppm of NTP host. Also you can do a similar check with a GPS module, e.g. Sparkfun EM-406A, tying its pps pulse to attachInterrupt()
and get micros() in the ISR -- (one change required for teensy was I had to set pinMode(pin,INPUT) for the interrupt pin. i didn't need that on UNO/DUE/maple). Results of crystal and resonators tests can be found at
https://github.com/manitou48/crystals
Each crystal is a little different, so your measurements may vary. Frequency is affected by temperature, voltage, age, and load capacitance.
and get micros() in the ISR -- (one change required for teensy was I had to set pinMode(pin,INPUT) for the interrupt pin. i didn't need that on UNO/DUE/maple). Results of crystal and resonators tests can be found at
https://github.com/manitou48/crystals
Each crystal is a little different, so your measurements may vary. Frequency is affected by temperature, voltage, age, and load capacitance.