The primary considerations when designing this project are precision and cost.
The frequency counter will operate at at least 50 MHz. The 74HC4040 chips can potentially be run up to 96 MHz, but it seems like one may need to test and select the best chips for the first, high-frequency input stage to achieve this maximum rating. Additionally, very high-speed comparators aren't cheap, and I'm trying to keep the entire BOM, including the board, to below $50.
The counter can operate in direct, reciprocal, or event counter modes.
In direct mode, the counter will have a 1Hz precision, +/- 1 Hz, with the timebase error added on top.
The counter will communicate via I2C with another microprocessor. The board is 'headless' -- there is no display included. The counter will be configured and read via I2C. (Setting the input signal setpoints will require knob-twiddling.)
Both the included timebase and the signal input modules will be easily swappable for upgraded modules. This will allow for user-created timebase modules or connection to a surplus rubidium source, and for upgrading the input modules for more flexibility and higher speed.
The board will run on 9-12V input and have an onboard regulator.