I've ordered myself an EA3GCY ILER-20 kit, and being a single-band QRP hand-tuned radio, I want a convenient counter. I'm going to be using this in the field on battery power, so it's got to sip the juice and be small (tiny!) and light. The design should be suitable for any small HF rig (and maybe 6 metres) with an easily accessible point to measure the VFO.
I put together a design and just ordered PCBs. BOM cost is on the order of $25 in single quantities, and a good $5 is the TCXO I selected in the interest of needlessly chasing accuracy. That should give it 10Hz resolution at ~10Hz refresh, with 0.5ppm stability.
The design is based around the VIM-878 LCD module I chose. This is an 8-digit 14-segment (starburst) LCD that seems about the right size for integration into a small rig. Next I picked the TI MSP430F4132 as main processor, thanks to its included LCD driver, cheap development tools (the $5 MSP430 Launchpad) and my relative familiarity with the architecture.
Basic topology will have an input amp driving an 8-bit counter directly, with the carry connected to a counter in the MSP430. The external counter is gated by the processor from a timer; the same edge also captures the carry count in the other timer module; the processor is clocked by the TCXO divided by 2 with a D flip-flop to get it close to the MSP430's maximum clock.
Boards should be here in a few weeks and I can start fooling around. I wonder if anything will work first try...