DIY Digital Computer/Major overkill LED flasher (few questions)

Discussion in 'The Projects Forum' started by doublebeta, Feb 7, 2010.

  1. doublebeta

    Thread Starter New Member

    Feb 7, 2010
    4
    0
    Hi!
    I am going (or thinking about going) to build a DIY computer using full adders with clocked inputs, and 3mm red/green bi-colour LEDs on the outputs. I don't know if anyone has done this sort of thing before (though I have seen DIY computers with flashy lights, I haven't found any using full adders, other than LED number display decimal adders (liek calculators)) It should run on a single 9v battery and 7805/78L05, but since it will probably draw a godlike amount of current, I will probably have to run it on 4x 9v in series, with several diodes and a 78(L)05 VREG. This will be my first real digital project, but I have done plenty of analog work, so I should be fine building it. To get a better idea of what I mean, this is the data for: http://www.falstad.com/circuit/
    Code ( (Unknown Language)):
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    84.  
    Ignore the switches, that was purely just for my testing, finished design won't include this.
    I am going to use 12 hex schmitt trigger inverter oscillators with frequency values that are primes, i.e. .02hz, .05hz, .11hz, .17hz, .23hz, etc. These don't need to be exact at all, but they need to be sorta close to their 'ideal' value :D.
    I am going to make it '16-bit', and therefore have 16 Bicolour LEDs on the output (with resistors). However, I need to know if I can daisy chain this: http://www.futurlec.com.au/74LS/74LS83.jsp (sorry if that's advertising...) together, with, (idk if this will work) C4 of the first chip going to C0 of the next, and so on, if you know what I mean?
    I will put the LEDs in an 'LED matrix', and the effect will be a 'programmable' LED flasher, and it will look AMAZING with the Green/Yellow/Red/Off flashing lights going for evermore (or until the battery runs dead).
    http://ledcalc.com/ says the value for putting 23.3mA of current through an LED from a 5v supply is 120Ω, with the resistor going before the LED anode. Can I connect the anodes of the bicolour LEDs to the outputs of the OR/XOR directly, and have a single 120Ω resistor to ground, to cut costs/difficulty?
    I am going to patch the clocks to the inputs with just insulated wire, because 130 banana plugs/sockets just isn't within my budget, and 5m of crappy wire is :D.
    I will build the entire 'computer' on veroboard, since I have NO experience with PCB design or 'printing'.
    I've done quite a bit of googling, and messing with the simulator to test some of this, and the base seems to be working pretty sweet, however, i've only tested this in a simulator. At these low frequencies, is noise going to be any problem with this? It's not a mission critical circuit AT ALL, but, is noise likely to cause anything to go wrong, including power supply noise?
    Also, incase I can't daisy chain the full adder ICs, can I get away with using a half adder with this? I'm quite new to digital circuits, so it's kind of hard to get my head around it and understand it properly.
    LEDs I will be using are http://www.futurlec.com.au/LED/LED3RG.jsp. They are common cathode(negative).
    If you think this is crazy(or that I am crazy, which I am ;)), see http://www.homebrewcpu.com/! That, there, is CRAZY. But awesome. Seriously, check that site out!
    I am also thinking of putting capacitors and resistors in parallel with the LEDs, to add a little bit of fading (very subtle amount!). I could also have a single transistor active lowpass, but 32 of those seems just a liiittle bit complicated for such a small effect.
    I have also thought of sticking a piezo element on each output and making a big mother clicky thing :D.
    I apologise if this is hard to read and understand, and if it is too long, but like the rules say, better too much information then not enough, yet I still think i'm forgetting to say something crucial! I tried to do a bit of paragraphing and seperation, but well, i'm no good at neatness, just look at that simulator data! :D. Please help me if you can :D.
    Feel free to yell at me if I did anything wrong! I also invite anyone to steal my idea, and you can sell it for millions (if anyone would buy it...), as long as you give me some credit for the idea (just write 'based on idea by doublebeta/Kyen Langton(my real name)).
    EDIT: Wtf, forum removed my crappy paragraphing (three spaces before text)! Oh well.
     
    Last edited: Feb 7, 2010
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    There is a command in LaTeX (the standard text standard of this forum) that will let you enter code verbatim, similar to how we enter pictures for schematics or whatnot. Never used it, but it is

    {code}{/code}, using [] instead of {}.

    with your code being between the words.

    BTW, if you attach a picture to the post you can link to it like this.



    with the URL being between the words.

    Hope this helps.
     
  3. doublebeta

    Thread Starter New Member

    Feb 7, 2010
    4
    0
    Added code tags. And also, I know about the standard bbcode tag, and I did read the post on using TeX tags in the electronics chat forum, but I just didn't think of it at the time :).

    Annnd, --BUMP--.
     
  4. doublebeta

    Thread Starter New Member

    Feb 7, 2010
    4
    0
    Hi! Sorry for double post!
    I looked through a datasheet of the same chip made by a different semi manufacturer that was better quality, and found that I COULD daisy chain a virtually infinite amount of these together (DIY Large Prime Finder, anyone?), which is awesome, but that I couldn't use the C1 C2 C3 carry outputs to light LEDs as pins for them are not attached to the silicon. So at first, I was like 'bummer, that sucks!', then I realized it was a reason to build a 32-bit system! (See attached schematic). And also, since it is only the real math outputs that the LEDs are connected to, I can do real 32-bit math with this! (or not quite, no carry on last chip, because then it would have been uneven for the LED matrix, but I can add it!). I am left with only lone major problem - it seems the adders are not capable of sourcing enough current to drive LEDs. Also, I don't think I can 'sink' the outputs because the datasheet says "LOW Level output current Max - 8mA". Have I got the whole thing wrong? It seems I will most likely not be able to drive them from the inputs, so, should I do transistor switches (see schemo) to supply more current to the LEDs, an opamp buffer(5v opamp = fail :p), or what? I have plenty of quad opamps, and can buy them cheap, so this might be easier than heaps of transistors, but I really don't know...can haz help? Can haz suggestions? Criticisms?
    doublebeta.

    Also, check out mah logo in schematic :D. 5mins in GIMP goes a long way, if I say so myself. Colour version look way better. It's two electrons leaving an atom, which would be under the 'aura' thing if I actually drew it :D
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Are you going to use red LEDs? The reason I ask is you may not have a choice, at least with the configuration you are thinking about.

    Red LEDs typically drop 2.5V. The BE junction will drop around 0.6V, this leaves you 1.9V to play with on the resistor.

    White/Blue LEDs typically drop 3.6V, going up to 3.8V. Add the BE of 0.6V and you only have .6 to .8V left, not enough to have a reliable resistance on, though if you are willing to tweak every resistor it can be done. 10ma @ .6V = 60Ω.

    It may be better to use a common emitter configuration, though it will take one more resistor per transistor. Design the base resistor to be 1/10 the current of the collector, so if your LEDs use 10ma you will need 1ma from the logic chips.

    Have you read this?

    LEDs, 555s, Flashers, and Light Chasers
     
  6. doublebeta

    Thread Starter New Member

    Feb 7, 2010
    4
    0
    Aha, actually I was just reading that page!
    I didn't take into account the drops of the transistor, oops, but it is okay, I can use 9v from the battery (and have 5v go to logic, see first post) and the transistor should not allow any current to flow into the base and damage the logic chips :D. I could even use a regulated 7v, and that would dissipate less power in the resistors, and since there will be 32 of them (!) using power in a regulator sounds like a better idea :D. Though, I don't know if that actually works, but hey, this is what experimental projects are about!
    EDIT:ah, i'm using green/red bicolour LEDs, that have similar characteristics. I think I have a link for them in my first post, thanks for the help!)
    EDIT2: Ah, ok so i'm bad at wording things, but, if both LEDs are equivalent reds, with 2.2fV typical and 2.5fV max for both LEDs and desired current of around 25mA, would it be all systems go for the Base high = on design I put in my schematic(I have no idea what this is really called...)? I'd use the regulated +5v rail the logic chips use with a 1amp rated vreg(Could drain close to one amp!!!, Should take 32x23.5mA +/- 10% for the LEDs in the rare case ALL of the LEDs go on, plus the logics, NO MORE than 100mA, or I might as well build a PIC powered MIDIBOX core ;).) , as it should be right at 2.5v per LED, and since all the LEDs are in parallel, so current is the only barrier then, and worst case scenario is that it nukes a 9v battery in 10 seconds flat. And I could try building it as it is with the simple switch, and if it all goes crappy, i'll set up a few with the common emitter topology and see if that works. And if the transistor isn't switching because it needs more input current, I could use a Sziklai pair, which have a lower turn on voltage than a darlington(thanks wikipedia). I really don't know why I said to use low gain transistors in my schematic. Maybe because the 2n2222A is commonly used for switching, and it has crap gain :D.
    Thanks, doublebeta.
     
    Last edited: Feb 8, 2010
  7. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Actually the 2N2222 is between 100 to 300 on beta, pretty typical for its class, a beta 300 is listed as typical.

    You sound like you have a firm handle on the situation in general. Transistors also make decent current regulators with a few extra components. However, with the numbers you're thinking of I doubt you want to go that route. The advantage is the LED color no longer matters.

    Here is an example of what I'm talking about, you would use Vcc as the digital input.

    [​IMG]
     
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