I ordered a bunch of 3.3v/8mhz ProMini Arduinos. I think a few 5v/16mhz parts got mixed up. I have searched but cannot find a good, reliable way to tell the difference. Does anyone know how it can be done?
There is silk screen on the back of the board that could have been used to indicate the difference. None of my boards are marked. The label on the main chip is all the same, except for what I think is a date code.
I suppose I could go by the symptoms. All of my Arduinos get hooked up to (among other things) a DS3231 RTC. The RTC comes with a utility to read and set the clock. When running, it reports the time to the Serial monitor once per second. On one of my Arduinos it reports the time several times per second.
Second symptom - On the suspect board the MicroSD card interface does not work. The interface works if I use it on another Arduino.
Third symptom - I wrote my own version of blink that flashes an LED on pin 8. On the suspect board it flashes the LED about twice as fast as it should.
It seems kind of a pain, though, to use these to tell which board is which. There should be some definitive characteristic such as a ROM byte or something like that. The only thing I have found is the stamping on the clock crystal. On units that work the crystal is stamped "A4". On the one unit (so far) that runs fast, the crystal is stamped "80".
Thanks - Bill Gee