On 15 Jul 2011, at 05:05, neutron spin wrote:
....are there any good reference documents that cover "Charlieplexing"?
There is a Maxim document that explains the concept. Google is your friend here. http://lmgtfy.com/?q=charlieplexing. If you cannot find it then there is a link to the original article on my web page link below.
In relation to nixie clocks, I have made two charlieplex clocks. A two tube and a four tube clock.
The two tube charlieplex clock using HIVAC XN12s can be seen on my website at http://www.clock-it.net/charlienixie/index.html
If you scroll down, you can see a short video of the clock running. Personally I like this little clock a lot. People who see it like it too, I think that is down to the blinky bicolo(u)r LEDs though.
If you want to build this clock, and a few people have already done so, then I offer a coded PIC at modest cost.
The system relies on doubling up on pins so that each pair can drive two cathodes, depending on which is high and which is low, the formula for the number of outputs available being N*N-1 pins. Thus six pins can drive 6x5 or 20 cathodes. Enough for my 16 cathodes and a few spares for decimal points, if I had any.
The system works well, but as only one cathode is on at once, I found that it drove four tubes dimly unless I upped the boiler pressure considerably, which may not be a good thing for long nixie life. In this case I drove 36 cathodes from 7 data lines. 7x6 gives a possible 42 outputs, so I had spares. A few spares actually give you some scope for routing the board to your best advantage if space is at a premium.
During construction the system can seem confusing, as it is unforgiving of open circuits anywhere. A disconnected wire causes all other cathodes in the same group to glow at reduced brightness. This is also apparent in my Charlieplex LED clocks. It can make a single fault look horrendous, but it will make you laugh once you realise what is happening.
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