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Shopping For A WWVB Synced VFD Tube “Nixie” Clock
After much hesitation (partially from them be listed as coming from “Moscow, Russia, Canada”), green 7-segment VFD tubes in small preamp tube format were purchased from eBay. The datasheet arrived via email, being about a page and a half of mostly white space, a part drawing without labeled segments, a short list of characteristic voltages and currents, and an even shorter list of absolute max ratings. From the specs, it does not seem like they need AC driving of the cathode filament. They should be here within two weeks to confirm this.
For the WWVB receiver circuits, suitable parts were located at Digi-Key, in decent stock quantities and prices. C-Max makes a range of low frequency tuned ferrite coil antennas with very small footprints, for under $3, as well as a demodulation IC suitable for use with the antenna, the CME6005. A module based on the IC is about $9, the IC itself is under $3.
Current plan for controlling the seven segment anodes and the grid on each tube, as well as interpreting the demodulated WWVB signal, is a large pin count AVR driving darlington transistor arrays. Multiplexing will be avoided in order to use the tubes at maximum illumination. The cost of a large pin-count AVR is offset by not having to purchase latches needed to drive the tubes at full duty cycle with less GIO. The TQFP-100 parts look suitable.
Information on NIST’s WWVB atomic clock synchronization transmitter in Boulder, CO is here.
Following are linked Digi-Key part numbers and datasheets for the C-Max WWVB parts.
- 561-1002-ND C-Max CMA-60-19 60KHz 19mm Ferrite Coil Antenna (datasheet)
- 561-1014-ND C-Max CMRR-6D-60 CME6005 Based 60KHz Receiver Module (datasheet)
- 561-1013-1-ND C-Max CME6005 60KHz AM Demodulator IC SSOP-16 (datasheet)
Posted by rmrubin 
September 2007