Hi- I was a member of the old Yahoo group and just recently rejoined the Google group, so I may be reinventing the wheel here, but I want to share the details of my latest Numitron design. Most of the Numitron clocks that I have seen on-line are based on the MM5314 which is a neat chip for this purpose, but it comes with a few drawbacks, the main ones of which for me are price and availability. The others are the lack of an easy battery backup and the large number of diodes needed to prevent ghosting when used with Numitrons.
Therefore, I proceeded to look for a more modern LED clock chip to attempt to use in this project. I found that most, if not all more recent chips are "duplexed" by segment using the 2 opposite AC phases rather than by digit like a 5314. This requires both a special power transformer with a center tap for the display and a higher voltage output for the actual chip. It also, of course, requires a specially wired LED display which would seem to preclude the use of Numitrons since all 7 segments share a common return path. A 4 digit clock was fine because I only have 4 DR2010s to use in this project, I started with an SC8560 (=LM6560) IC which seems to be a fairly common/cheap duplexed clock IC. I am sure that there are others that could be used in a similar fashion. I am using a bank of transistors to demultiplex the output of the SC8650 in order to allow conventional drive to each segment of the Numitron. I am also using a phase inverter circuit to generate the out-of-phase drive to the 2nd bank, therefore allowing the whole clock to be run from a single-ended 12V wall wart. At this time, I am reducing the 12V to 5V for the Numitrons with a simple transistor pass regulator, but I will probably refine that some more since it is having to dissipate about 5W and gets a little toasty. At this point, I have the circuit debugged on a breadboard (and have pictures!), and am preparing to draw up the semi-final schematic if anyone would like to look at it. Al -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
