My Nixie tubes have 11 active pins each: a common anode and one cathode per digit (ten in total). The anode is connected to +180V via a 47k current-limiting resistor and each cathode is connected to the collector of a high voltage bipolar transistor (MPSA42) so that current can be controlled through each of them via the base of the transistor. This gives a total of 29 transistors that need to be individually controlled (24 hour clock requires 3 possible numbers for the first digit, 10 for the second, 6 for the third and 10 for the fourth). I chose to do this by using four 8-bit shift registers, connected in series to make one, 32-bit shift register.
A geometric series is a series of numbers where each number in the series is equal to the previous number multiplied by a constant multiplication factor. For example: 2, 4, 6, 8, 16… is a geometric series with a constant multiplication factor of 2.
The sum to infinity of such a sequence, then, can be represented as:
One big change since I did the first version of the clock is my access to professionally made PCBs. At the time, I was only able to produce PCBs via hand etching or using my home-made PCB mill. A board like this requires at least a double sided design which is not easy using the above methods and so I used veroboard. This is painfully slow and messy.
For the new version I will use a professionally made two layer PCB.
I’m replacing the screen on the logic analyser for a few reasons: The CRT is heavy and bulky – replacing it would make the whole thing lighter, an LCD could be brighter and I can add colour to the monochrome display, and on top of this it’s just an interesting project. The most important thing is that the replacement screen is not worse than the old one!
After putting this project on the back burner, I am focusing on it once again. Brian HG on the EEVblog forums suggested that a simple line doubler would make the signal compatible with most modern VGA displays. What that means is that each line in the frame needs to be repeated twice, at double the speed.
Currently we get a new line every 40 microseconds, but this is too slow for most displays to be happy about. Therefore, if we record each line and output it twice at 20 microseconds each most VGA displays will be ok with it.
The robot box needs to know when it has reached the limit of it’s motion. If motion continues past this point, the machine will literally rip itself apart. To stop this happening, I am using a limit switch that will be pressed if the robotic finger move too far. However, it seemed that a good portion of the time the robot would ignore this button and continue to rip itself apart. The reason for this lies in the way I was using interrupts to detect the pressing of the button.
I really like my Nixie Clock that I built two years ago – but I don’t like to leave it on when I’m not around. The reason for this is that the Nixie tubes are powered directly from the mains which means that touching the Nixie tubes could result in a dangerous electric shock. While the tubes are protected under glass I don’t like the thought of someone accidentally tripping over it and getting electrocuted. So I decided to redesign the clock.
I am going to power the clock from a 9V wall supply and boost that voltage up to 180V to light the Nixie tubes. While this is still quite a high voltage, it is isolated from the mains and is much less dangerous.
My design is largely based on Threeneuron’s Pile o’Poo.