Vacuum tube single digit calculator

Forget that newfangled silicon. Hollow state is king!

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This project is for folks who just cannot add single digits in their head, on their hands or using other methodologies taught at an early age.
This monstrous machine containing a bunch of vacuum tubes, power transformers, neon displays and a ton of other parts makes short work of adding single digit numbers in a flash.
Fun for the whole family! Also can keep the family warm on cold days as the tubes pump out megawatts in heat dissipation.
The extras include a card reader for even speedier input and a pushbutton keypad so your fingers don't get so sore moving the onboard slide switches.
This baby is ready for mass production! I have planned to restart 7 tube manufacturing operations in a retirement community in Florida, and take on at least 600 skilled workers for the point to point soldering work. Add a 3 D printer farm with 1500 printers to generate the massive amount of plastics required for mounting stuff and viola! All puns of course)

Lets dig into some juicy details!

This calculator can only add,subtract, multiply and divide single digits. This also includes the answer digit-It can only solve a number up to 9. Please use your damn fingers and toes for sums exceeding the machines capability.

Using all vacuum tubes for switching this relies on the power of the pentode to form flip flops using a single tube. Its lightning quick processor speed is about 1 khtz(SO Fast) and gives answers speedy quick. The large display eliminates the need for glasses and are made from neon bulbs. The power supply sports an unholy 5R4 rectifier pumping out enough heat to prepare a 3 course dinner for two. An OA3 regulator keeps the high voltage B+ in check and stable during operations.

The card reader uses 3 D printed cards specially formulated with magnetic dots to rapidy enter numbers and functions(+,-,* and divide) quickly and outputs to a massive bank of relays that interface with the machine. I also added a massive keypad using the largest and bulkiest pushbuttons I could find for input.Another massive bank of relays interfaces this keypad to the CPU.

If you are forgetful of your sums I also wired in a thermal printer to print out the results of your calculating labors. It does require a wall wart power supply but don't worry it is much more energy efficient than the rest and you will barely notice the extra load on your electric bill using it.

You just have to really appreciate the speed that this thing can carry out stupid simple math! What a wonderful age we live in.

And lest you forget, the tube circuitry is immune to typical silicon frying EMP. You can sit in a dirtpile that used to be your home after the apocalypse and do simple math as long as your generator keeps running.

  • Adding the seven segment neon display

    castvee82 days ago 0 comments

    The project thus far has demonstrated the ability to load a couple of numbers and add them. The sum was presented on a few neon bulbs, but that is sort of like listening to R2-D2 speak...It is much more presentable if the output displays a real number so I added the module for a display.

    This also gave me a chance to use my edgecard connector boards! The above shows the entire system with the new display module on the far right.

    Here is a close up of the display module in operation. Ahhh..the soft glow of neon.Sure beats just a single neon bulb glowing eh?

    It is clear the machine beast is taking on a life of its own-the sprawl is getting out of hand but that just makes it more fun.

  • The triumph of the triode

    castvee805/04/2019 at 00:56 2 comments

    So with the pentodes performing perfectly I took to tackling the triode circuitry for creating a latch and adder. The 6SN7 tubes each contain two triodes in a single envelope and after mounting everything up the latches looked like this:

    I made everything for this testbed on a small module plate so it could easily be traced out. The neon indicator show the status of each triode.

    This module was created as an input device.

    It contains pushbutton switches and neon indicators that allow input. The final module also contains two triodes and is configured as multiple gates.

    By adding the various inputs it produces a logical output. I got a board made at: to actually hook up the seven segment neon displays to this testbed. Will get it built out and photos coming soon.

    Here is a look at all the modules connected and ready to run:

    The modules in the rear are power supplies and an additional filament transformer.

    I will be adding more modules to this testbed later. If you are going to experiment with this sort of thing I recommend making it modular. You can plug and play, test things and re-arrange things easily.

  • A pocket full of Pentodes

    castvee804/30/2019 at 00:54 0 comments

    The question that must be burning in everyone's mind at this point(sarcasm) is how does this thing work, what are the tubes doing and how is it all wired up.

    Trust me you will be sorry you ask but I have some time so here we go.

    I made this demo plate with two tubes mounted and wired. There are two pushbuttons(green) on for each tube that serves to latch the tube. A third black button clears the latches. If both tubes are latched, the resulting is a nand gate and the output appears at the top binding post. This plate is a nand gate, an inverter and a latch all in one, with outputs for all depending on how it is wired to the rest of the plates in the machine. Each tube may be just used as a gate or and inverter or a latch or any combination.Neon bulbs(in the large holes) indicate the status of the tubes state. The tubes are 7 pin miniatures and of type 6au6. I had a horde of them and also there are lots of others with the same footprint that can be substituted. I also have a bunch of 6KD6 and others that work perfect. No worries about loading, they are basically just driving neon bulbs. The pentode make a nice clean toggle in digital type apps such as this. There are dual triodes that also would reduce size and filament current but they do not make that nice snappy state change.

    The green plate is a 3 D printed affair with holes for tube mounting.I don't normally need to drill holes in the thing but with these demo versions I had to add binding posts.

    Normally there are 4 tubes per plate, but it gets really congested on the point to point wired side so I dropped two tubes for clarity(yeah, right). Point to point is always sorta messy and congested, but it wires up easily and requires a very minimum of other terminations.

    You will also note the use of binding posts for power connections. I don't normally use these in a hardwired machine, but as a demo its nice to be able to probe around a bit.

    The same few values of resistors are used throughout the circuit. 47K,100K, 1K. Interfacing of plate use the same values.

    This is a test power supply I use to verify a module is working:

    It consists of three power sources=High voltage B+. negative bias and filament voltage. The tube are 5R4 the rectifier, and an 0A2 for voltage regulation. The voltage regulator keeps the B+ very stable when bunches of tubes are switching states.

    This is the test supply all plugged in and ready to go. The test supply is 120 vac mains powered. You gotta be careful with this stuff it bites pretty hard!

    Here is a demo video.

  • My bus runneth over...I.O.

    castvee804/29/2019 at 03:27 0 comments

    Imagine yourself building a single digit calculator and then running off the end of the earth expanding it via bunches of I.O. gear only to find your bus will only play with one accessory at a time...Sadness ensues. But wait..A fix is in sight.

    Here is the I.O bus I made for the calculator. It is a single row 32 pin port made from a cheap header with .1 spacing. Terrible planning I should be flogged with a sharp piece of thorny wood.

    The solution of course was a simple expander-Make two out of one. Since the accessories all have relay isolation between them I was able to pull the rat out of my pants and fix this unholy mess easily.

    The fix was just a simple pcb from OSH with the connectors male and female stuck in the right directions.

    I now return you to the regularly scheduled project...Please stand by. I will do my very best not to let anything like this happen again.(sarcasm)

  • Scratch built hard drive

    castvee804/28/2019 at 03:11 2 comments

    What's that you say? Yes, I built a hard drive for the calculator to store those pesky single digit numbers I keep forgetting. I could have easily just made a relay matrix to store the numbers, but like everything else in this project I felt the need to extremely overdue it...yet again.

    The basics of the beast are the same as regular old fashioned drives. It has a spinning platter, sense arms to magnetize and demagnetize spots, and is tracked as to position so it can find them. There are a few tiny differences. First, the spinning platter is rotating at about 8 RPM. It is stationary until a button is pressed and at which time the platter makes one revolution. If a toggle switch is in one direction, data is read or writes to the drive. In the other the data is erased. It is simplistic as there is no system control from the CPU to run it, everything had to be rather automatic. Once the two numbers are input and visible on display the button is pressed and they are stored on the drive. They remain on the drive until erased. By simply pushing the button the numbers load into the machine. The drive stores 8 bits(2 nibbles).

    It would be a simple matter to store many more numbers on the disk-lots of space left over(actually I think it could store 64 bits) but again there is no address system to recall more than the machine can process in real time.

    The erase arm is a motorized offset lever arrangement that sweeps an electromagnet over the magnetized spots and removes them. The write magnet is affixed over the platter and is nonmoving.

     The entire assembly including platter is 3 D printed. Two motors run the mechanism, one driving the platter and the other the swingarm for the erase head.

    The platter is printed with depressions to hold a blob of metal powder and acrylic paint mixed together. I experimented with the mess until I found the right density that I could easy mag and de-mag. 

     The trick I found to be useful is to spend equal time magnetizing the spots and demagnetizing them. Sounds incredibly basic but its important. It also takes a specific amount of time to accomplish this, hence the slow moving platter.

    The platter is indexed with small circular magnets and a reed switch to track current position. The motors are small gear type running on 5 Volts. All the power to the drive comes from the CPU as the other accessories I made for the calculator.

    I plan to work on a method to add more storage and recall next. Seems such a waste to have all that capability and use so little of it(sarcasm). I am already envisioning multiple stacked platters!(sarcasm)

    Video coming soon.(I am so very tired...)

    If you find yourself trying to build your own hard drive for a single digit calculator, you have obviously missed something else you should be doing. But it was loads of fun and some frustration figuring it all out. Sure, now that I know how to do it the next one will be easy...…

    After completing my hard drive and testing it I called to my assistant :

    Me: Watson, come here I need you. I just scratch built my first hard drive, ran a single equation and now its full!

    Watson: Dumbass!

    End of line.

  • The external input keypad

    castvee804/26/2019 at 19:14 0 comments

    At some point playing with this contraption I found myself growing weary of moving those slide switches up and down. It is hard on the fingers, it is a rather slow way to enter data and it just makes sense to make a keypad pushbutton affair.

    The main sticking point in doing this is the switches connect and disconnect bias voltage for the vacuum tubes and it important to keep those voltages isolated and allow other input devices to make use of the input bus.

    The gigantic pushbuttons each trigger and latch a relay. As can be seen a rather large umbilical cord is brought forth from keypad to Cpu as a result.

    There are 8 data relays, a clear(which drops out power to the latched relays) and a function button for adding, subtracting, multiplying and dividing.

    The whole mess is smashed into a 3 D printed box like affair with a bunch of wires flailing about..

    I am low on supplies and had to use one color of wire for most of the jumpers to the connector.

    This entire assembly is in fact a very low tech affair but it works perfectly. Now doing single digit stupid math is no longer a finger pain affair.

  • Upgrade? for neon display-go for the dot matrix!

    castvee804/26/2019 at 04:33 0 comments

    For the life of me I cant see why I went through all the trouble for this but...Here we are. I really like the neon  segment displays-all glowy orange and taunting me with that retro light. But there is work to be done I made a neon dot matrix display that can be swapped for the seven segment version.

    I have no idea why I arrived at a 5 X 6 Matrix. But as soon as I hooked it up and tested it I was so very impressed with myself.Its a 3 D printed housing that holds the ne-2 bulbs and has a connector on the back for wiring. Its not that its some revolutionary thing, nor even close to high tech.

    It does take a bit more decoding to make functional and the last thing I really don't need to do is complicate the simple machine I have built. But in the grand scheme of things this could certainly have other apps for future vintage stuff. 

    The real kicker here is it is SO cheap to make. A 3 D printed frame, 30 Ne-2 bulbs and some dropping resistors. I assembled this one in twenty minutes and wired it up. Its performs flawlessly. These can be stacked also and possibly do some goofy graphics.

    Or perhaps I really have gone insane....

  • How does that card reader work?

    castvee804/26/2019 at 00:23 1 comment

    This log was by request. I was asked to share some details on how the card reader worked and share some details. It is embarrassing simple...I hope you are not disappointed.

    Here I go....And please stop me if you have seen this before!

    The card reader is of the magnetic sensing type making use of reed switches that are activated by tiny magnets embedded into the card. The card is arranged so it presents 2 nibbles of data to the sensors, a set for the first digit of the equation and a second set to the second digit. In between these two is a function selector which tells the reader to add,subtract,multiply or divide. The reed switches must be laid out carefully so adjacent switches are not activated by magnets not intended to be selected. I laid them out in a staggered row fashion to avoid just this issue.

    The magnetic embedded cards. You can note the cards have a finger slot on the front to prevent wrong direction insertion and the slight dimples are the magnet locations. The cards are of ample size to work well with two sets of input nibbles and a function selector....but no more. If you want to scan more bytes make the cards bigger to prevent unwanted triggers.

    The reed switches are wired into the relays trigger circuit-The relays are first wired to latch on a low signal from the Cpus ring counter. It is just a simple sequencer that counts up to 5 and recycles. After the first four counts the final is a reset pulse so you can start over with another card. Of course you need to shut off the card reader power switch as the relays are wired to latch. Its kinda a wiring mess as I did it all just point to point.

    Here is a simplified circuit to show some of the wiring for a nibble. Sorry for poor sloppy schematic-I haven't drawn a real schematic since 1982. It is all brutally simple-The relay contacts(which provide 100% isolation to the tube wiring) just make the tube filp flop...flip same as if you were sliding the input switches on the console. Once the flip flops are selected a function pulse is sent and the answer appears from the flip flops outputs. When you hit reset everything returns to off state and you are ready to do some more simple math.

    The frame and reader parts are all 3 D printed and everything just glued and screwed together. This thing could really be built more awesome and universally useful in a larger scaled up card. You could squeeze in double, even triple and have a card a bit more capable. Perhaps not as a storage medium but as a controller initiation or some such. Or not...

    The cards could and should be printed with deep enough pockets to hide the magnets and unused pockets just filled in. I made tiny cover caps to hide them.

    It is all really simple-But it is a fun way of data entry and to make some flashcards!

    Hope this was helpful.....

  • Prototyping the tube circuitry

    castvee804/25/2019 at 17:59 0 comments

    This type of circuitry allows me to make use of a 1970s style prototyping system called Lab-volt Modular.

    These sets were state of the art in the day and often used in schools for teaching electronics. I have a MASSIVE amount of these systems as I held on to them over the years and even added on a bit from Ebay and other sources.

    There are two circuits built here using the tubes as flip flops. The power supply on the back supplies B+ voltage as well as bias and filament voltages.

    I used toggle switches as input simulators. Once a switch id flipped it remains on until reset regardless of the toggle switches state.

  • Card reader and printer demo videos

    castvee804/25/2019 at 17:06 0 comments

    This video shows how the cards are read for stupid simple math:

    You can hear the relays click inside the reader as the ring sequencer turns each on and the data is fed to the vacuum tube Cpu.

    This video shows how the card reader sends data to the Cpu then how it is printed onto paper. A pushbutton switch attached to the printer signals a cts (clear to send)and the printer squirts out the results.

    This is a video of a relay calculator I made that also has a cardreader:

    Same idea-slightly different approach-This uses printed bumps on the card that trip sensors underneath

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Enjoy this project?



Dave's Dev Lab wrote 04/25/2019 at 22:59 point

can you post some documentation on the card reader?

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castvee8 wrote 04/25/2019 at 23:10 point

Sure. Coming soon to a project log near you.

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castvee8 wrote 04/26/2019 at 00:25 point

Card reader log is up-Say,how about a like on this project????Please???

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Dave's Dev Lab wrote 04/26/2019 at 17:44 point

dandy! thanks! done!

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castvee8 wrote 04/26/2019 at 18:55 point

Thank you so much for the like!

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aquaticedge wrote 04/25/2019 at 17:31 point

is this a neon tube type display? 

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Dan Maloney wrote 04/25/2019 at 16:10 point

Neat! We featured those displays a while back I think.

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castvee8 wrote 04/25/2019 at 16:28 point

Yes and I was mocked horribly for trying to replace the nixie...….

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Dan Maloney wrote 04/25/2019 at 17:11 point

Haters gonna hate...

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sjm4306 wrote 04/25/2019 at 18:54 point

Lol the tag line for hackaday should read: "Welcome to the hackaday comments section, come for the banter ... stay for the vitriol!"

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castvee8 wrote 04/25/2019 at 19:43 point

Thank you for the fine comment. I was expecting to be harpooned with a giant dull rusty spear!

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