Paulie over at the EEVBlog made a great little lab frequency standard.
Playing around with my new $10 Ebay frequency counter I noticed it was a few counts off from my old 10mhz reference dug up out of the toolbox. Specs for the oscillator claimed 1ppm/yr and it was coming up a bit outside that. It wasn’t obvious whether the TCXO in the counter was off or the one in the reference.
Come Saturday I took advantage of the local ham club shortwave receiver to do some zero beat tuning with WWV and turns out they were both off enough to explain the difference. Both dead on now. Another club member had also purchased one of these counters and used my reference to get his in tune. He wanted to build a cheap standard for himself so I flashed a chip and he was good to go. It occurred to me others might like to throw together something similar. If there’s interest I can put up a file and diagram. Anyway here’s some photos.
20mhz TCXO can be had on Ebay for a buck or so. This particular unit runs off a single AA cell. It can be alkaline or rechargeable lithium or NIxx. I prefer lithium AA because it can sit on the shelf for years and still have full charge. One of those $1 USB DC-DC converters boosts to the necessary 5v. At 50 cents for the AVR total cost was 3 dollars and change including case and push button.
Update: Hackaday covered an updated to this project. Checkout the update: