I had seen an interesting project that was a watch utilizing an ATTiny85. However, there were concerns about both power consumption and the accuracy of the internal oscillator for time-keeping. I was hoping to integrate a 32.768khz watch crystal to it, but was unsure of how to do it exactly. I understand I am likely asking something simple, and apologize in advance. If I could be referred to a guide for how to do that with the Arduino IDE and a Uno, that'd be great. Thanks for the help.
The most obvious question is why not use an RTC chip for time keeping and the internal oscillator to run the processor?
Too little space on the board, unless you can suggest a good smaller chip. Also, power saving, due to reduced power use at a lower processor speed.
If you clock the Tiny off a watch crystal (by setting the fuses appropriately), it will run at 32.768 khz, as far as I can tell. Is that really fast enough for your application? Also, you may have to take special measures to slow your programmer down enough to write to it after setting it to run at such a slow speed.
Well, the Low-Frequency Crystal Oscillator section of the datasheet has everything you need. Connect crystal + capacitors to XTAL1 and XTAL2. Change the CKSEL fuses.
You will have to program the target at 32768 / 6 = 5461 bits per second or slower. To get that slow of a bit rate you will probably have to buy a quality programmer or adjust the ArduinoISP sketch. Uploading a full image will take at least 12 seconds to burn + 12 seconds to verify.