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Registered Member #561
Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230
I've been thinking of building a mains synchronous clock, with a catch; using only digital logic, vacuum tubes, and nixie tubes. The biggest problem I foresee, besides the large number of tubes I will need, is turning a 50hz signal into a 1hz signal for timing, I know you can get IC that do it but I wanted to do it using tubes. Has anyone seen anything that might help? or if it's even possible?
I probably won't be able to get round to this till I've got some surplus cash, but for now I'd like to get this problem of my mind :P
Digital vacuum tubes just seems so odd to me, which i why I think it will be an interesting challenge, before anyone asks
Registered Member #4034
Joined: Thu Jul 28 2011, 10:41PM
Location: somewhere in the Southern hemisphere
Posts: 138
a 50bit Shift register? would take alot of tubes though... to save tubes you could have 2 10bit shift registers with one output onto the other's input/ clock.
Registered Member #561
Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230
50 bits is way to much, I'd be looking at hundreds of tubes for that
Even 2 10bit registers would be a lot. I'd be better off increasing my counter from 17bit to 22bit and having my counter go 24:60:60:50 instead of just 24:60:60
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
I don't think that the frequency is stable enough to use as a counting source. Unless maybe you can calibrate it once and a while? Then again, the error wouldn't propagate as much as it would doing the same thing with an inaccurate 1MHz clock.
To get the timing signal, you could use a 16 bit counter, the MSB would flit at about .0015Hz. Then multiply this by 659 (probably the hardest part in terms of number of tubes). This would give a clock of about 1.002 Hz. Your clock would still be off almost 3 minutes each day, needing to be calibrated. Of course, the more you divide it and then multiply back up, the more accuracy you will get. For instance a 32 bit counter with the MSB multiplied by 42918455 will give a clock of 1.0000000015 Hz. I'm pretty sure this is how the IC's do it, but when they can hold millions of transistors there isn't a problem with space.
Registered Member #561
Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230
mattster_mac wrote ...
I donno 100's of tubes for an essentially pointless task sounds great to me :P may I ask why you are using tubes?
I know they used to use them in the first computers, but tubes and digital logic just feel like opposites to me :P, thus why I want to use them. Still though, I don't have the budget to buy hundreds of tubes, I'd like to minimise the number used to save my wallet
Turkey9 wrote ...
I don't think that the frequency is stable enough to use as a counting source. Unless maybe you can calibrate it once and a while? Then again, the error wouldn't propagate as much as it would doing the same thing with an inaccurate 1MHz clock.
To get the timing signal, you could use a 16 bit counter, the MSB would flit at about .0015Hz. Then multiply this by 659 (probably the hardest part in terms of number of tubes). This would give a clock of about 1.002 Hz. Your clock would still be off almost 3 minutes each day, needing to be calibrated. Of course, the more you divide it and then multiply back up, the more accuracy you will get. For instance a 32 bit counter with the MSB multiplied by 42918455 will give a clock of 1.0000000015 Hz. I'm pretty sure this is how the IC's do it, but when they can hold millions of transistors there isn't a problem with space.
Apparently it is stable enough, they used to use this type of clock before quartz clocks became popular, except they were electromechanical instead of digital. When the frequency is slightly off during times of heavy demand, they counter correct it at night (if it was a bit slow during the high demand period they would speed it up during low demand times), this is so this type of timer stays accurate, I figure they are more common than we think and thus the electricity providers maintain this system
I'm probably going to just divide each second into 50 and increase the counter to 22 bits, seem like the cheaper option
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
You can divide the line freq by 5, 5, and 2 to get 1Hz. See You can also use astable multivibrators or a relaxation oscillator (see 2D21) oscillating at some freq and then synced up by pulses.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You can't do it with just logic gates, you need flip-flops. The Eccles-Jordan circuit was a classic building block, made with the two sections of a dual triode tube.
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Getting a 1hz signal from 50hz mains using only logic gates
