The long discussion about designing one's own versus buying a kit determined me to write about my first experience in the matter.
It started with a Nixie display module bought from a hamfest (Friedrichshafen), in 2008, a module that included the Nixie tubes and 74141 drivers. No HV supply, no documentation of any kind. The module included 10 tubes, 2 of witch were letters and symbols (M,m,G,u;Hz,V,A,Ohms), 8 with numerals. At that time it just seemed an unusual type of display and I thought it would be an interesting challenge to try and use it for some purpose. A clock was the obvious choice, since it seemed quite simple to implement. At the time I had almost nonexistent electronics knowledge (besides the basics; e.g. I did know what a transistor did but did not know how to connect it, drive it, etc). Since I write software for a living I thought the simplest way would be to use a microcontroller, but it wasn't something I was familiar with. However, one of the books I found at the ARRL booth was "PIC Basics" (by Cliff Powlesland, G8CQZ) and I bought it thinking it would provide some useful pointers to microcontroller programming. It was a good choice, as it had some electronics instructions along the way. I believe that trying to create something from scratch is a better learning experience then simply copying something that already exists so I decided to create my own design. This was made easier by the fact that the "display" module already had the drivers connected to the nixies; after some searches on the internet I have found the datasheet for the 74141 drivers (thanks Dieter - I think your site was one of the first to provide such information back in 2008), so by following traces I could figure out the module pinout. I also found the datasheet to the tubes and figured out the needed voltage. I used a 220-110v transformer (I live in a 230v country - close enough) and found the resulting 160v dc to be enough to light up the tubes. The first test (I did not know if the module would work or not) was to simply power it up with HV and see what happens - all digits lit. I figured that I should pull the inputs to ground so I did that, connected the remaining input to ground and indeed one digit was lit. This test was done with all inputs in parallel, so in fact it was one digit for each tube. I started experimenting with the uC. I have bought the kit recommended in the book (Velleman K8048) and the 2nd example provided with the kit was enough for what I wanted to do next. Since there were 8 tubes, I connected them in 2 groups of four, to drive them from the 8 bit port of the uC. This seemed to work, as well. Along with the kit, I bought a few TTLs, including some 74LS373 registers, to experiment with. Well not much in the way of experiment - their use seemed pretty straightforward. The approach was as follows - I used 3pcs 74LS373 registers to maintain the outputs. All PORTB pins from the PIC were used to connected to the input of the registers (8 bits) while 3 PORTA pins were used to SELECT each register. The datasheets (along with some ideas picked up from the book) were enough for me to manage to get a different digit lit up on each tube. After that it was just a matter of programming to get a clock running. I added two buttons for setting hour and minute and everything was pretty much working. By the way - I used the 4MHz crystal as timebase as well, setting up a timer in the PIC that would "tick" every 100ms (IIRC; I should check the sources) and this proved surprisingly precise. I suspect this has to do with minimizing the crystal error - n ppm error at 4MHz means a smaller part of a second than n ppm at 32768Hz. So now I had a nice nixie clock but with a big bulky transformer from 220v to supply the tubes. This part took a little over a week of vacation (but it was more than full time work - from wake-up until going to sleep I was working on this). However this also sparked an interest in electronics that has not subsided yet. In the end. the design is obviously primitive and lacking all of the features of other clocks (most annoying being lack of battery backup, since we tend to get power failures around here). I have planned for the past 3 years to design and build another, more advanced one, but there are always some other things that get in front. By the way, besides the power supply (which by itself took some months in all) the case proved most difficult for me. In the end it's only two black pieces of plywood with holes for the tubes - just as primitive as the rest. The 2 rectangular buttons for Hours and Minutes (what was in my mind to pick rectangular ones? I think it was the only thing I found at the time) are dangling from a small wire. But it's the first physical thing that I created (software seems so ephemeral). And for 3 years it has worked flawlessly in our bedroom, it stays on at all times (except when we are on vacation) and still works. Pictures took during various development stages are at http://hawk.ro/ceas/index.html -- 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 https://groups.google.com/groups/opt_out.
