The Cardboard Computer - IO is my name

My goal is a 4-bit cpu using discrete transistors. I am learning from scratch as I have never worked with hardware at the gate level.

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Attempt to build a computer using cardboard and brass paper fasteners as the base material for all of the logic circuits. Why? Well, the cardboard is free as my workplace puts it in the dumpster and I do not have the funds to buy better material. All of the electronic parts thus far were given to me by a friend who passed away and what better tribute than to build a computer. Except for the ALU all gates are either Nand or Nor using DTL. The transistors used are npn 2n2222 type or pnp 2n3906 as I started having a large stock but now facing the need to buy a lot more for this build to continue. Very large construction is employed as to aid in my learning about logic circuits and also to make it easier to make changes as I find out what does not work. Each gate measures about 0.75 X 1.75 inches on cardboard cutouts. RISC will be required as this is a 4-bit system and the clock speed will be very slow at about 3Hz. The main bus is 8-bits ( 4 for data and 4 for address ).

Thanks to -

Cardboard computer video update 1

Cardboard computer video update 2

Cardboard computer video update 3

IO - The Cardboard Computer update 4

  • 1 × 555 timer ic chip
  • 130 × 2n2222 npn transistor
  • 95 × 2n3906 pnp transistor
  • 230 × 1n914 Switching diode
  • 462 × Resistors Assorted common values
  • 1012 × Paper fastener Paper fastener found in any big box store
  • 63 × LED Fiber Optics / Emitters
  • 6 × Capacitor Switch debounce RC

  • February 25, 2017 - Cardware is now here

    Mark Nesselhaus4 days ago 0 comments

    Took time off today from IO to work on a project named #Cardware with HexHammer

    If anyone has an interest in DIY robotics then this is a project that needs following. Lots of neat things are going into it so please follow along with this adventure.

  • February 14, 2017 - The Cardboard Computer has a name

    Mark Nesselhaus02/15/2017 at 01:00 2 comments

    The Cardboard Computer has been given a name. Meet IO which stands for Inside Out. Jez @HexHammer and I had been talking about our projects and such and the term inside out from Pink Floyd was mentioned. That was the spark and rest might be history. What better name than for something that would normally be in a box or enclosure to now be on the outside........

  • February 13, 2017 - Converting ALU input levels

    Mark Nesselhaus02/14/2017 at 01:46 2 comments

    Spent some time today wiring up a circuit to convert the lower 5 volt logic 1's to 12 volts. I am using just a basic non-inverting buffer using two not gates for each input of the ALU. So far I have one board that takes care of the A inputs. Next I will wire up the same board again for the B inputs. The photos below show the ALU and the newer level converter board. I will be adding some leds as power indicators.

  • February 12, 2017 - Logic level voltage issues

    Mark Nesselhaus02/13/2017 at 00:08 0 comments

    I have used today to get my old 4-bit adder working with the rest of this computer. I am having some logic level voltage issues between the adder and the rest. The adder was designed and wired a year ago as a stand alone project to operate at 9 to 12 volts and most of the rest of this computer operates at 5 volts. I have been able to get the adder output to latch into my new register. However, The lower level outputs from the other stages are not high enough for the adder/alu inputs. I will try using buffers at the alu inputs to boost to the higher level voltage that the alu is looking for. It's either that or rebuild the alu and I really do not want to do that.

  • February 8, 2017 - 1 nibble memory with pnp nand gates

    Mark Nesselhaus02/08/2017 at 18:48 2 comments

    I have been working on a replacement for the PC register that I had before. I was not pleased with how well it worked and decided to switch to pnp transistors. The following photos show what I came up with and the steps in writing and storing data. In this case the number 2.

    This is the register input and output zeroed.

    This is the number 2 selected on the input.

    This is 2 on input with deposit selected ( far right switch )

    This is 2 latched on the output.

    All four bits are latching and all is well except that when any of the input switches are set to one, then there is a little back voltage to the deposit led. This does not affect the memory from working and at least it lets me know that there is something to deposit ;-)

  • February 5, 2017 - And now for something different

    Mark Nesselhaus02/06/2017 at 00:12 5 comments

    Just dug out something from my junk box of parts that I almost forgot about.

    I used to be very active with crystal radios and one day I wanted to see if I could make my own variable capacitor. Using two soda cans, a cardboard ( what else ) loo tube , electrical tape and a plastic tube, I was able to come up with this. Wired up with a crystal radio set it tunes quite nicely on the mw broadcast band here in the U.S.

    Hope this gives everyone a smile :-)

  • February 4, 2017 - Sequencer installed

    Mark Nesselhaus02/04/2017 at 11:41 2 comments

    I have taken some time off of the actual build to study this project but now starting to melt some solder again. The sequencer has now been mounted to the main frame and is working very well. I was having a problem with the J-K flip-flop toggling without error. It would hang up from time to time and freeze for a couple of clock cycles and then resume again. Just by chance, I installed a led to the output of the pulser circuit and not expecting to see anything due to the short duration of the pulse. I do get a nice flash from the led and now the J-K is toggling without any glitches :-) I can only surmise that the led is placing a slight load on the pulser circuit but beyond that I am open to thoughts about why it works better.

    Here is the result so far. The pulser is at the top right with the pulsed led on the right side of the board. The toggled J-K is in the middle and the sequencer is at the bottom with five steps that I can branch from. Sorry for quality but cheap camera ;-)

  • January 21, 2017 - Trouble in paradise

    Mark Nesselhaus01/21/2017 at 16:02 7 comments

    Ever have one of those days where nothing goes right? I have been rewiring my program counter and using a circuit that is known good by a number of sources and yet no matter what I do, I can not get it to do anything. Just sits there mocking me. Oh well, that's the price I pay for taking on this project. Never fear, I will figure it out. Transistors and diodes test good. Wiring checks out and solder joints making good contact. I will survive , I will win :-)

  • January 17, 2017 - Power/ground bus wiring

    Mark Nesselhaus01/17/2017 at 14:48 9 comments

    Taking a day to wire up a master power switch and power / ground bus module. With this I will route power and ground connections to each panel. The module is nothing more than the switch and more brass fasteners at the top of the I/O panel.

  • Over all view of current construction

    Mark Nesselhaus01/15/2017 at 00:20 8 comments

    This is currently where I am at with this build. Does not look like much but when wiring the way I am then time drags on :-)

    Same confusing circuits but now with a new look. At least it will now fit through the room door when it is time to move :-)

View all 23 project logs

  • 1

    My basic nand gate

    I guess that this could be called a single 2 input nand gate IC . Just very large scale.

    Start with cardboard and brass fasteners

  • 2

    Layout the parts needed.

  • 3

    Solder the parts to the cardboard base

View all 5 instructions

Enjoy this project?



esot.eric wrote 02/21/2017 at 07:57 point

Interesting quote, there in the details regarding public-labs. And you already know I think this is a cool project.

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Mark Nesselhaus wrote 02/21/2017 at 08:12 point

Hey there :-) The quote just struck me the right way and I really hate to conform so David let me use it :-) I like working and thinking out of the box ( Ohhh I just had to say that ) :-D

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David H Haffner Sr wrote 02/20/2017 at 23:56 point

Hey Mark, your "baby" is looking very cool, actually I think I'm going to find some old pics of the CP901 (similar to the CPU in the P-3 Orion back in my day) man this thing is really looking the best way!

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Mark Nesselhaus wrote 02/21/2017 at 00:47 point

Hey thanks David. There is a lot more to go before even the first instruction flows through but it is coming along and I am learning a lot :-)

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HexHammer.Jez wrote 02/17/2017 at 11:02 point

Hi Mark!

Thank you for the invitation of contributor to your awesome project... Its a cardboard revolution! :-)

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Mark Nesselhaus wrote 02/17/2017 at 22:23 point


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Mark Nesselhaus wrote 02/21/2017 at 00:49 point

Hey Jez, That's a revolution on two fronts ;-)

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J. Peterson wrote 01/18/2017 at 22:12 point

This is incredible work. My one caution is the choice of cardboard as a circuit substrate. If anything shorts or overheats, it’ll go off like a bomb. Corrugated cardboard is particularly bad, because the spacing within it ensures there’s plenty of oxygen to fuel the fire.

Please think about this. If nothing else, keep an extinguisher handy, and don’t leave it running unattended.

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Mark Nesselhaus wrote 01/18/2017 at 22:19 point

I am making sure that all stages are running cool and very low current, but perhaps placing milliamp fuses in various places would be wise :-) I had not thought about the fire hazzard till now :-O

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K.C. Lee wrote 01/18/2017 at 22:47 point

Don't know how reliable this is.  With the good old Borax...

>This technique will only work for natural materials such as wood, cotton, jute, and paper or the like.

Read the comment part.

BTW stand alone vertical arrangement of paper burns the fastest, but there aren't much fuel.

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Mark Nesselhaus wrote 01/18/2017 at 23:18 point

The Borax is something to look into, will have to test first as to how conductive the Borax would be as well as how the solution would affect the glues in the cardboard. Thanks for the link :-)

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Ted Yapo wrote 01/18/2017 at 14:45 point

Congrats on the blog writeup!

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Mark Nesselhaus wrote 01/18/2017 at 15:11 point

Thanks Ted, I still have a long way to go and lots and lots to learn :-) I am currently redoing the PC from ideas and nudges from you all. ( getting rid of the pulser boards...)

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Ted Yapo wrote 01/18/2017 at 16:08 point

Nice.  I saw you mention you don't currently have a scope - that's probably where one would help most.  How fast do you think your clock will be?  If you can test it at less than 20 kHz or so, you can use a sound card as a low-frequency scope - a quick search should turn up some software solutions.  Some soundcards (like those used for some software-defined-radio projects) go even higher than 20 kHz.  I used a soundcard-based spectrum analyzer to test some audio noise generators, and it was surprisingly good.  I haven't played with a soundcard scope for a long time, but I'd be willing to bet there's something decent out there.

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Mark Nesselhaus wrote 01/18/2017 at 19:23 point

Hi Ted, I do have some sound card scope software here that works well, however right now my clock is around 3hz and that is below what the scope can see. Not a major problem yet and I will speed things up once various sections start talking to each other :-) And you knew about the blog before I did :-)

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Mark Nesselhaus wrote 02/21/2017 at 01:38 point

I am going to keep one pulser  for the sequencer circuit as that might be the only stage that will require edge triggering.

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Yann Guidon / YGDES wrote 01/08/2017 at 08:46 point

Wait... Why would you even need a 555 ? :-D

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Mark Nesselhaus wrote 01/08/2017 at 09:04 point

Well, I was having my doubts about the transistor osc signal being clean enough ( Was still in the dark about level triggering ) and used the 555. I will change back to transistor later, just not a priority at the moment :-)

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Yann Guidon / YGDES wrote 01/08/2017 at 09:35 point

Another cool circuit to try...
You know, you could use a basic classic astable oscillator with 2 transistors to generate a square-ish signal :-)

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Yann Guidon / YGDES wrote 01/08/2017 at 09:40 point

however the astable oscillator is more delicate/fragile/picky than a relaxation oscillator or an inverter-based, hysteretic oscillator... Just add an amplifying stage (or two) to create proper edges :-)

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Mark Nesselhaus wrote 01/08/2017 at 10:05 point

The astable was what I started with but again, I was/am new to this and was not sure at the time :-) Well, time to get breakfast ready for the residents at work. Yumm

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HexHammer.Jez wrote 01/02/2017 at 13:33 point

When an artist's work grows too big to move, he calls it an Installation...


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HexHammer.Jez wrote 01/01/2017 at 13:18 point

Awesome project! Seeing this took me back to my early teens reading about Babbage and Turing in the village library, playing with electronics kits and discovering the school had a BBC Micro in a cupboard in the Maths Room that nobody knew how to use.

I'd like to draw your attention to Nyles Steiner's ( experiments with Memristors. These are simply-constructed doped crystal junctions that exhibit programmable resistance. The device then is a passive 2-pin solid state memory cell that could be used to provide EEPROM type memory for your processor, perhaps to store commands in?

In operation, a single gate is programmed with a high forward voltage (9v) which makes the junction thereafter conductive to a low forward voltage (3v) and highly resistive to a low reverse voltage. A high reverse voltage makes the junction thereafter conductive to a low reverse voltage and highly resistive to a low forward voltage. The device is behaving like a Tunnel Diode that can be made to change polarity by over-driving it. The gate can then be tested with a smaller voltage to determine polarity and thus state... Which is stored physically in the crystal lattice, requiring power only to read or change its state.

I have successfully followed Nyles' experiment and built a 6 bit 'flash' memory cell using an Atmel, a handful of 3904s, LEDS and some scrap copper and aluminium, but it appears you have more ambition and patience than I ;)

Hacky New Year...

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Mark Nesselhaus wrote 01/02/2017 at 01:42 point

Thank you for the awesome :-) I have looked at the idea of memristors a little bit but for this project I will stay with what parts I have on hand. Back in the late 70's A group of friends and I built a Imsai 8080 and had a ball learning to catch the rabbit on the led display. No keyboard or video then for us :-) I would at least like to repeat that program on this machine.

Hacky New Year to you as well..

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HexHammer.Jez wrote 01/02/2017 at 09:04 point

I just have to admire the look of Cray super, with a hint of Practical Electronics that has about it besides what it actually does. Literally old school... You sir, are an artist.

It was just those brass studs begging for a little sulphur and a tinfoil hat that appealed to my artistic nature as well as my sense of humour. There is a delicious irony in constructing things from ingredients, its a sort of alchemy... I have a thing for copper myself, it is beautiful, structural and its oxides sensitive to heat, light and pressure as well as having electrical memory. I've built many experimental devices and sensors using copper, household chemicals, heat and water just to learn from. 

One must however respect cardboard. ;-)

Hmmm. Around then I remember being ushered into Careers, a room with a large table littered with cards; farmer, postman, lawyer... In the corner was a box with a keyboard and a screen, a CBM Pet. It wasnt even switched on.

"Oh, thats a computer," the Careers Officer said. "Pay no mind to that boy, it will never catch on." I'd love to go back and show him the waterproof battery powered touchscreen computer I wear on my wrist today, a direct descendent of the BBC that inspired me to wait all these years for it to become small enough.

I wish you luck with your endeavour.

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Mark Nesselhaus wrote 01/02/2017 at 11:44 point

Good morning, Well, I guess that every thing we do or construct is alchemy in one form or another. Just keep that cup of coffee away from my cardboard ;-D  I do wonder if my studs will work that way, might have to remove any protective coating first. That melts away when I solder. I sure would like to get my hands on a Pet. My first comp of my own was a trs-80 and a few zx-81's. As the years move on, I find I no longer can keep up with the internal workings these days. I am 60 and want to go back to more basic times so this project might scratch that itch :-)

I might have to change the shape as I can see that I will run out of room. Might have to put the panels on a wall but I do like the cray type shape. It will be heavy to move around.

Take care

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David H Haffner Sr wrote 12/30/2016 at 11:58 point

Hey Mark, I think I understand a part of what you are doing now, you are utilizing a large part of your present inventory of components. I should have read further in the details section, you did mention the '2222's, I am trying to think of something simpler that can be used that is just as effective. 

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Yann Guidon / YGDES wrote 12/30/2016 at 03:38 point

If your wife complains, tell her you got 1.6k views already. Amazing !

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David H Haffner Sr wrote 12/30/2016 at 00:34 point

Well Mark, you are certainly thinking outside the box...and I luv it!

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Mark Nesselhaus wrote 12/30/2016 at 00:41 point

I hate say to say this but instead of thinking out of the box.... I'm using it :-D

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David H Haffner Sr wrote 12/30/2016 at 00:50 point

Ha ha, yes, you are right, a hint...using a 2n2222a (NPN)  can be used for small signal switching, if that helps.

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Mark Nesselhaus wrote 12/30/2016 at 01:52 point

Currently I have used up all of my 2222's . That is why I switched to the 3906 pnp's I still have. I still have about 180 of them left. I still have around 130 1N914 diodes.

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Yann Guidon / YGDES wrote 12/30/2016 at 03:34 point

If you need a few hundreds of BC550 and 1N4148, just tell me where to send them ;-)

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Mark Nesselhaus wrote 12/30/2016 at 09:50 point

You got Yann :-)

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David H Haffner Sr wrote 12/29/2016 at 21:56 point

This is very clever! 

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Mark Nesselhaus wrote 12/29/2016 at 23:03 point

Thanks, I am thrifty by nature and am having fun and learning at the same time on the cheap.

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David H Haffner Sr wrote 12/29/2016 at 23:24 point

Man. this is a lot more than "thrifty," I almost think it boarders on ZEN-like! My present project is the first 1 of mine, that has the sophistication that it has, though most of the parts I design myself to save money.

I was thinking about those bimetallic blinkers for Xmas tree lights as make shift switches, but I think their response time would be way too slow to be even effective for this project. I don't know, I'm always thinking of the weirdest things!

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Mark Nesselhaus wrote 12/29/2016 at 23:48 point

Weird is good ( sometimes ). I have made a lot of ham radio projects that were no more than 3 or 4 transistors so this computer is way over the top for me. My wife asks me how are we going to move this thing if we relocate in a few years. I have no idea. One of many good things about HaD is thinking out of the box. By building ourselves, we can flex our thinking as much as we want to and share with other weird folks :-)

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Yann Guidon / YGDES wrote 12/30/2016 at 03:39 point

You nailed it, Mark :-)

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Mark Nesselhaus wrote 12/29/2016 at 19:27 point

I went shopping today at a Habitat restore ( thrift store ) and bought a string of holiday white LED's for 1 dollar. It's a rats nest of wires but seems to be over 200 LED's so not a bad deal. At a initial look each LED runs at 3 to 4 volts at 3.75 ma. I self destructed one at 5 volts. Now I have plenty for this cardboard project for my output display panel.

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Ted Yapo wrote 12/29/2016 at 20:26 point

Great idea - they have leads already attached, too :-)

I have often thought about cheap incandescent holiday bulbs for homemade PROMs inside a diode array - apply 12V to program (burn out the zero bits), and normal logic levels to read.  Just replace the burned bulbs to erase.  Incandescent strings  are becoming tougher to find, though...and you would have to avoid those burn-proof ones with the shorting links around the inner terminals.

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Mark Nesselhaus wrote 12/29/2016 at 23:01 point

Not only the LED's but all of the wire will be used on the build as well. I went to Wally world also hoping to find the same but only the incandescent types were still on sale., the led strings were already gone for the season. Now back to soldering the dmux gates :-)

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Mark Nesselhaus wrote 12/23/2016 at 08:53 point

Well.... The ALU and decoder boards are using thumb tacks on wood bases. The wood I had to buy, the cardboard is free, lighter and easier to cut to size. As far as leakage, just have to wait and see. I could apply a non-conductive coating first but then I would have to spend money and I am a cheap builder :-)

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Shaos wrote 12/25/2016 at 06:23 point

So it was thumb tacks initially? :)
I chose the same approach, but with "Cork Tiles":

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Yann Guidon / YGDES wrote 12/25/2016 at 07:01 point

Apparently a new trend has been created ! :-D

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Mark Nesselhaus wrote 12/25/2016 at 09:17 point

Yup. I had constructed some radio projects with thumb tacks years ago. I can't take credit for the idea as I found a project online back 15 years that used them.

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Mark Nesselhaus wrote 12/25/2016 at 09:19 point

The thumb tack revolution has started. Yesssss !

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Stuart Longland wrote 12/25/2016 at 23:13 point

Here I was thinking, "Well, I'll use thumb tacks for now but will replace it with something better later"…

Still haven't gotten around to the "something better" yet… and that antenna still goes.

Having seen the comments here, I don't feel so guilty.

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Ted Yapo wrote 12/23/2016 at 01:40 point

At first I thought they were thumbtacks, and couldn't figure out how they stayed put :-)

Those fasteners are a great idea!

If you end up with leakage issues in humid environments, you could also substitute corrugated plastic board:

Although I'm not sure how well it stands up to soldering...

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tomwsmf wrote 12/21/2016 at 15:21 point

Amazing project. Very hands on and very informative. This makes for a great deep look into how our tech shizzlewhizzle works under the epoxy blobs and TOS. Please keep adding notes and sketches here on Hackaday. 

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Mark Nesselhaus wrote 12/22/2016 at 12:30 point

Thanks, there are quite a few out there that have done this but for me it is both a learning aid and perhaps a strange looking piece of art.

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Just4Fun wrote 12/21/2016 at 14:15 point

OMG!!!! :)

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Yann Guidon / YGDES wrote 12/21/2016 at 03:15 point

Please, upload some schematics :-)

What do you use to mount the parts ? I've never seen this method before :-)

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Mark Nesselhaus wrote 12/21/2016 at 09:21 point

Good morning Yann, As soon as I figure out Hackaday I will get some sketches of the circuits I am using. The metal paper fasteners on cardboard is used for a few reasons. 1 I'm poor, no extra money to buy better material. 2 it spreads out the parts so I can better learn what is going on visually and 3 it looks kinda cool and almost a art form in itself. The gates are attached to the main cardboard frame using hot melt glue.

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Yann Guidon / YGDES wrote 12/21/2016 at 13:43 point

You could write a log that explains your unusual but smart method :-)
For example, a step-by-step How-To with several pictures ?
Who knows who it might inspire in turn ?
Regards :-)

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Yann Guidon / YGDES wrote 12/21/2016 at 13:44 point

Oooooops too late :-D

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Mark Nesselhaus wrote 12/21/2016 at 13:53 point

Yup, started posting some instructions. Now it's time to get dressed and go to work. I'm a chef at a assisted living facility and there are some days I feel like I need to live there :-)

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coletonn wrote 12/21/2016 at 14:14 point

Yeah that would be nice. See how the thing ticks. 

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zaphod wrote 12/20/2016 at 15:20 point

this is pretty impressive

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coletonn wrote 12/20/2016 at 18:36 point

Ikr. This gives me a headache. 

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Mark Nesselhaus wrote 12/21/2016 at 01:10 point

Thanks, so is yours. you have inspired me to keep working at this.

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