The Cardboard Computer - IO is my name

My goal is a 4-bit CPU using recycled cardboard substrate and Diode Transistor Logic. This is an educational platform for me.

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My goal is to build a four bit computer using recycled, re-purposed and just plain junk as the main construction material. 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. A very green build indeed. The first electronic parts to start this 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. Thanks to Yann Guidon and Jezz - Morning Star for additional parts. 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 used and the clock speed will be very slow at about 3Hz to start. The main bus is 8-bits ( 4 for data and 4 for address ).

Added a clock speed control to IO

Replaced the 555 IC with a astable circuit.

2's complement works well for counting down.

October 19, 2017 - Power usage for IO at about 1.5 watts / 5 volts

October 12, 2017 - IO's theme song. Pink Floyd - Wearing the Inside Out

September 24, 2017 - IO has a new 7 segment display.

August 27, 2017 - Update, All the current sections of IO are working together.

HACKADAY Wheels, Wings and Walkers 2017 contest entry.

Cardboard computer video update 1

Cardboard computer video update 2

Cardboard computer video update 3

IO - The Cardboard Computer update 4

  • 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

View all 7 components

  • A possible output device for IO

    Dr. Cockroach03/02/2018 at 17:11 7 comments

    Found this Smith Corona Typewriter for $8 and it works fine. No, the Hello World is not from IO... I might be able to patch IO into the keyboard electronics so please pray for me on this one :-)

    The keys press a small rubber? coated finger across the meshed contacts so I think that the contact is acting like a capacitor. Going to begin mapping out the matrix...

    So far so good. The contacts are simple make and break. Makes the use with IO a little easier :-

    So here it is March 4, 2018 and I have cobbled up a plug in adapter to where the keyboard ribbon cable connects to the main board. Take a look at the progression and either shake your head or chuckle a little but the connection is rock solid.

    At least this way I can restore the typewriter back to the way it used to be later :-)

    Here is how the connector has mapped out.

    All wired up and ready for input from IO :-)

    Just at the point where IO is able to send a signal to the typewriter with each sequencer cycle. This is just the beginning.

  • ROM card read logic board - March 2, 2018

    Dr. Cockroach03/02/2018 at 13:03 4 comments

    Starting to layout the construction and wiring for the logic board that will read the program ROM cards. Just like all other wiring on IO, this will be a large board...

    The ROM back plane will mount above the logic circuits...

  • Edge Card Connector Construction

    Dr. Cockroach02/20/2018 at 23:17 0 comments

    I have streamlined the construction of my 5 contact edge connector to where I can produce the number that I need for Brainwarp. What follows is a pictorial step by step for making a cardboard edge connector. One thing to note is that the contact center to center is 3/4 inch. Materials are cardboard, brass paper fasteners and hot melt glue.

    As of February 22, 2018 I now have 10 connectors just about finished.

    This is the Mock-up of the Brainwarp ROM motherboard. Still needs six more connectors.

    Here is the actual backplane with the first two edge connectors glued down and soldered.

    Now have ten connectors wired to the back plane with six to go.

    Ok now, here is the finished 16 four bit ROM back-plane. I never would have thought that I would ever make cardboard connectors.

  • February 15, 2018 - IO needs edge connectors

    Dr. Cockroach02/15/2018 at 23:19 3 comments

    Edge connectors made with cardboard ? Yup

    This is a side project for IOs Brainwarp. The magnetic cards are not making very good consistent contact over time so I am looking into rolling my own edge connectors using my usual cardboard and fasteners.

    What can I say,. It's pure Uglytech :-D    But it works..... Muahahahaha

    February 16, 2018

    Well, it works with the addressed test board so I think that this is a go :-)

  • February 10, 2018 - Diode ROM test board

    Dr. Cockroach02/10/2018 at 23:21 1 comment

    Testing the logic for a diode ROM to be used on the Brainwarp entry panel. So far so good as it is working as expected. This test panel uses 2 bit addressing to select between 4 memory addresses with 4 bits each.

  • Speed control for IO - January 30, 2018

    Dr. Cockroach01/31/2018 at 02:04 4 comments

    I have added a very basic speed control to the master clock circuit.

  • IO running on the new clock and flip flop

    Dr. Cockroach01/26/2018 at 14:15 7 comments

    I have hooked up the new astable multi-vibrator and master slave flip flop to IO and the sequencer. Looking good :-) Yann has waited a long time for this ;-)

  • January 25, 2018 - Master Slave J-K Flip Flop for IO

    Dr. Cockroach01/25/2018 at 13:45 0 comments

    Got a bit distracted with the IO project ( Now how can that happen ) and decided to wire up a new ( for me ) flip flop circuit. Yann has wanted me to ditch the 555 as a clock and the pulser circuit from the start and now is the time :-)

    By using a master slave flip flop I can get rid of the pulser and replace the master NOR flip flop with a Nand logic master slave. This is also the start for building a 4017 Johnson Counter using this master slave :-)

    And here is a video of the new flip flop in action  as well as using the new clock circuit.    

  • January 11, 2018 - Leds everywhere

    Dr. Cockroach01/11/2018 at 10:07 0 comments

    I was starting to run low on my led supply for IO and then along comes a New Years gift so to speak. I frequent my local Habitat Re-Stores almost every week and they put out items that did not sell or not in good enough condition to sell.

    Habitat for Humanity is a great organization that helps build and provide housing for those who do not have the financial means to do it on their own.

    This week it was a box of 14 led fabric decoration kits that were old and the internal batteries corroding. Overall there are 140 leds for IO. Red, yellow and green should be nice in addition to the blue/white leds I have been using :-)

  • December 4, 2017 - Cell Pointer register

    Dr. Cockroach12/04/2017 at 11:07 2 comments

    I have been a bit slow with updates but many chores have kept me away from the IO project. Melting some solder these past few days and the Cell Pointer boards are almost wired up. I really want to get the Brainwarp instructions up and working before the end of this year :-)

    December 5 and the Cell pointer register is wired up :-)

    Decided to wire the power and ground buss with bare wire as well as the enable line.

    After wiring this register and then another I thought that it would be best to wire up a test panel to make sure I had things right. Glad I did as the second register had a few issues. The test panel again uses house lighting switches and a micro switch is used for the enable function.

View all 61 project logs

  • 1
    Step 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
    Step 2

    Layout the parts needed.

  • 3
    Step 3

    Solder the parts to the cardboard base

View all 5 instructions

Enjoy this project?



Dr. Cockroach wrote 04/21/2017 at 19:58 point

Want to welcome @Dylan C.

To the Cardboard Computer team :-)

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David H Haffner Sr wrote 03/21/2017 at 11:29 point

Hey Mark, I see you entered your project for the 2017 prize! I'm really glad you did and the best of luck my friend :)

  Are you sure? yes | no

Dr. Cockroach wrote 03/23/2017 at 23:45 point

Hey thanks David, If nothing comes of the contest then at least I am having fun. It's interesting to see just how low tech I can be and still do this. Like in the T.V. ad,"  Even a caveman can do it " :-)

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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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Dr. Cockroach 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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Dr. Cockroach 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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Morning.Star 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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Dr. Cockroach wrote 02/17/2017 at 22:23 point


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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Morning.Star 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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Morning.Star 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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Dr. Cockroach 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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Morning.Star 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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Dr. Cockroach 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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