7400 competition: Entries and reader’s choice

Here’s a (hopefully) complete list of entries in the Open 7400 Competition. Please share your favorites in the comments below, your favorites will receive a special reader’s choice prize. Voting ends in 24 hours.

A few commentators will receive free PCB codes as a thank you for voting.

Check out the list below.

A huge thanks to everyone who voted. Judges are deliberating now, final results will be posted by November 10th.

Join the Conversation


  1. My favorites (assuming I can’t vote for mine) are the constant load with nixie readouts, and the Class D amplifier using digital logic.

  2. I’m a humongous fan of the passive RFID tag. It’s unbelievable both how much power you can get out of the reader and how little power the collection of logic chips consumes (go CMOS!)

    However, I would have to throw a vote to the 4049 Inductance meter because it is a useful thing made out of really old tech that I now want to build!

  3. I’d have to say the constant load with nixie readouts. It’s useful and the nixies are a nice touch.

  4. I’m torn between the sheer ingenuity of the Build Your Own FPGA and the Retro feel of the DIY keyboard.

  5. All are awesome and I cannot choice only one :D
    Simplicity : 4049 inductance meter
    fun : Mr. @#?%!…A 74xx based Q*Bert-ese obscenity generator
    usefulness : CMOS Frequency Counter
    best effort : 7400 Based Digital Calculator
    design : CD4000 Digital Alarm Clock
    brilliant : Constant load with nixie readouts
    complex : Data encryption and decryption system using 74xx logic gates
    awesome : Passive RFID Tag from 7400 discrete logic

  6. Since I’m to modest to vote for my own “Constant load with nixie readouts”…

    I give my first vote to the awesome “Passive RFID Tag from 7400 discrete logic”
    and the second to the definitely cool “Data encryption and decryption system using 74xx logic gates”.

    1. and also after checking 7400 Logic Based Calculator ,, i will choose 7400 Logic Based Calculator” as my first choice

  7. Since I am more of an analog person, I was impressed by the the extreme measures of the Class D amplifier using digital logic (hasn0life) using buffers in parallel to get the necessary amount of output current.

    I was blown away, however, with the “build your own FPGA”.

    The circuit I want to actually replicate is the inductance meter, it might save me money :D

  8. In this order: the home-grown FPGA, the DIY 6502 computer, and the 4bit SAR. And a special award to the BrainF**k machine :)

  9. My vote has to go to the the DFPGA (“Build your own FPGA”), for not only an interesting project but also a fantastic writeup.

  10. I will also vote for the “Build your own FPGA”. It’s a really awesome project and might be very useful for educational purposes.

  11. My vote is for the Constant load with nixie readouts. I think it was the nixies that did it for me and the fact that I need an other piece of equipment on the bench.

  12. That RFID tag is mind blowing. I’m buying one if he ever decides to mass produce.. The FPGA thing is nice too, but the wildest over-engineering is most definitely the RFID.. (over-engineering is a good thing, haven’t you heard?)

  13. I would vote for my own entry which is ‘Data Encryption and Decryption System using 74xx logic gates’..but if I have to choose another one, it would surely be ‘Build your own FPGA’..really awesome build Nick!! :)

  14. I like mine of course, the CMOS Frequency Counter :) But I take my hat off to the Passive RF Tag’s creator who has done a tremendous good job in his circuit, I really like it! Nice design and idea!

  15. Totally the RFID chip, most complete setup on the board
    2nd the DFPGA, just because I like FPGAs so much :)

  16. I’d like to vote to my 1 bit microcontroller :)

    If it isn’t possible, my vote goes to “Build your own FPGA”

  17. I vote for the class D amplifier (cause I made it…)
    My personal favorite though is the BrainF*ck Machine, I really like unusual computer architectures, and I think it’s great to have a “functional” computer using 20 readily available logic chips.
    Of course, the other entries are also pretty amazing….

  18. My first place vote is for the DIY 6502 computer. For second place I vote for 7400 Logic Based Calculator. There are a lot of great entries!

  19. I’m really impressed with the RFID tag. To even think of doing this is amazing!!!
    (Guess I wish I had the time for engineering something so completely out of the ordinary (and useless ;-))

  20. I would vote for my own entry which is ‘Data Encryption and Decryption System using 74xx logic gates’

  21. I have seen your work behind this.. No one can think about it.. Awesome guys.. you did it…

  22. “Data encryption and decryption system using 74xx logic gates” is the clear winner here .. My votes for that brilliant idea !

  23. “Data encryption and decryption system using 74xx logic gates” .. My votes for the best one !

    1. heh yeah, it says it was made by students so it looks like either it’s an entire classroom of people who worked on the calculator or just someone and then got the class to all vote on it

      popularity contest, oh well

      i liked most of the projects, my favorites were the q*bert, fpga, keyboard, and all the game projects.

      i would have liked to see video of the dds, brainfuck, and some others that didn’t have video though

      1. I hope this doesn’t scare off future contest participants from entering because they can’t (or don’t want to) get a group of people to vote for them. I also hope this doesn’t become a trend. Maybe there should be some kind of qualifications to vote? Also, were there judges this year?

      2. We figured it was ok because anyone was welcome to recruit friends and family to vote. We did not however count the vast majority of votes that were put in the wrong place (eg on the entry instead of here).

        There were 6 judges from the community this year, but we also included reader feedback in the ranking system and grand prize winner.

      3. I would have preferred that only proper registered forum members could have voted out of fairness reasons. I’d say that the winner of the grand prize is on the very thin line between just following the rules set by DP and cheating. It would have been all to easy to make a small script that via TOR would have voted 4000 times with different names and ip addresses on my entry.

        But since all of this is “just for fun” I really don’t care too much. I just hope that the winner make good use of his selected prize…..

      4. I think it would have been fairer if only other competitors could vote for the reader’s. It’s easy to register on the forum just to vote, so I think enforcing forum register is not strong enough. Also It’s a bit sad that the most important voting category this year was indeed a popularity contest, with not to do with the criteria stated at the begin of the contest.

      5. I’m sorry you were disappointed by the approach. I’ll definitely consider your suggestions if we every do something like this again.

      6. If you’re in the mood for constructive criticism, my input:

        – I don’t think Reader’s Choice was a bad idea, but when there’s few enough votes that a small group of legitimate voters (eg, a uni class) are enough to swing the vote, it’s going to be very prone to bias – less about the project, and more about who made it. That’s always going to be the case, but it’s more noticeable when the number of votes is small.
        – I think the choice of the grand prize should have been left up to judges, not readers.
        – I really would have liked to see more stratification in the prize levels. I realise one of the motivations was probably not to string out the process of giving out prizes too much, but I honestly think 15 first place winners is too many. It would have been much preferable if the judges had divided into categories with much more granularity.
        – A short blurb from each judge about what they liked about this year’s entries, which entries particularly impressed them, what they thought was particularly novel, and so forth, would have been awesome.

        All that said, thank you for running an awesome and inspirational contest. I’ve learned a lot both from building my own entry and reading about others’, so what more could I really ask for?

      7. It is great to see student entries IMO especially from outside Europe and the USA – hearty congratulations to the winners!

        In future I think it would be nice to have a separate student prize category mainly to stimulate entries from students but perhaps it might also help sidestep some of the classroom voting issues.

        Thanks also to the anonymous judges on the forum.

  24. Data encryption and decryption system using 74xx logic gates is the best among all these projects.I would definitely vote for it.

  25. ‘Data Encryption and Decryption’ using 74xx logic gates would be a good one. I vote for it….

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