Shop OBEX P1 Docs P2 Docs Learn Events
Gate-Mania — Parallax Forums

Gate-Mania

TbagTbag Posts: 31
edited 2006-01-18 22:02 in General Discussion
Hey folks,

I am an avid SX user but I have a design I want to implement in this case without the SX. I have a 12bit binary counter from ON semiconductor running at 40 KHz. I want to tap the binary numbers decimal equivalent to 125, 126, 127 (1111101, 1111110, 1111111 respectively) to a gate so that when those numbers occur, it will output a HI signal. My rudimentary approach will be to cascade each bit into logic gates but that creates a lot of gates! For example 1111111 would require 7 gates (about). Before i know it I need about 20 or so gates. Does anyone know a more efficient design? My TTL cookbook wasn;t very helpful for this.


Mr. T

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-01-17 22:44
    74HC688 8-bit magnitude [noparse][[/noparse]binary] comparator (cascadable) --
    http://www.jameco.com/wcsstore/Jameco/Products/ProdDS/46113.pdf


    ·
  • pjvpjv Posts: 1,903
    edited 2006-01-17 22:46
    Hi Tbag;

    Sure, use an SX........... only requires one (gate) package.

    Cheers,

    Peter (pjv)
  • TbagTbag Posts: 31
    edited 2006-01-18 03:34
    PJ that was very helpful. Thank you.

    PJV...hmmm...doing video with the SX are we?
  • pjvpjv Posts: 1,903
    edited 2006-01-18 04:31
    Hi Tbag;

    Sorry, I hope you did not take me too sarcastically, as I had not intended it that way, and I apologize if I offended you.

    The point I was trying to make was: if you don't like the solution that uses multiple chips, then why on earth would you NOT use an SX, especially if you are an "avid SX user".

    I just don't understand why you would not go for what appears to me to be the absolute optimum solution..........perhaps if you had explained we would not be so mistified.

    If it's the coding (and I doubt thats the case) I'd be happy to help you; this task is VERY simple.

    Cheers,

    Peter (pjv)
  • TbagTbag Posts: 31
    edited 2006-01-18 04:58
    I was not offended at all - just amused. I, for one, am very sorry for putting you on the defensive. My wit was slow and that is ALL I could come up with. : ) ! And your point is well taken. My circuit triggers an 18v transducer and I don't really know how to electrically connect the Sx into that situation as it requires 9v (a stable 9v). I don't really know how "to home brew it". Also how do you program SX chips if you eventually want to commericalize your circuit before shipping? I almost feel GUILTY Peter for underutilizing this chip for this particular need: using such a powerful chip to turn on a transistor for three 40KHz bursts and then waiting for 3.7ms and restarting the cycle. It just doesn't feel right using such a good chip for this. That's pretty wierd I know. The receiver is another story - I'm gonna burn that SX chip up! I am using the SX for reception. I just wanted to manage a purely low-end solution for the Tx.

    Thoughts Peter?

    Mr. Tbag

    Post Edited (Tbag) : 1/18/2006 5:01:34 AM GMT
  • pjvpjv Posts: 1,903
    edited 2006-01-18 05:34
    Hi Tbag;

    Well, there's no point feeling guilty about underutilizing the SX if other issues such as size, convenience, external component count, cost etc. are best served by its use. After all, should we feel guilty while an idle processor sits in a loop, effectively doing NOP's?.............. I mean all those wasted cycles! But the good thing is it's got an un-ending supply of them so the word "waste" is really not meaningful.

    OK, so much for philosophizing, now to work!

    So if the task is to repeatedly activate (presumably power) the transducer for 3 counts out of a 12 bit counter, this is simple for an SX, and possiby all that is required is a transistor to gate the transducer "on", or possibly to apply power to the transducer for that period.

    If you could give some further details about how the transducer needs to be powered/activated I'm sure we can help, or better yet, guide you in how to accomplish this.

    Also could you specify the stability and current requirement of the power supply; the SX can possibly also handle the regulation of the 9 Volts for you.

    As far as programming commercial quantities goes, it's no different than for prototyping unless you have thousands to do.

    Cheers,

    Peter (pjv)
  • TbagTbag Posts: 31
    edited 2006-01-18 20:32
    The transducer draws from an 18 volt supply switched through a push-pull circuit driven by a TTL signal (from the SX). So I need to step down the voltage from 18 to 9 and make sure that when I blast the tranduscer for 75us from 18v I don't cause a dip in the 9v power supply to the SX. Strategies on this would be greatly appreciated. Currently I have an 18v 1 amp wall transformer doing the job.
  • jb1311jb1311 Posts: 20
    edited 2006-01-18 20:49
    There are several options but the SX is the one I would use.

    1. Build AND gates using Resistor Diode Logic or Resistor Transistor Logic.
    2. PAL or GAL - cost is similar to SX and you need to have someone program it.
    3. Use an EPROM with the outputs of the counter as the input to the address lines - cost is similar to SX.

    I have used all these options at one time or another. These days I use a microcontroller for almost everything. Even as a 555 replacement.
  • TbagTbag Posts: 31
    edited 2006-01-18 22:02
    OK, I get it. I don't feel so bad anymore. I want to make a homebrew SX "board" that is a fraction the size of the Protoboard that they sell. I have that one and it is too big for my use at this time. How do I scale the whole thing down to a much smaller area? Can I use a breadboard with the DIP SX?
Sign In or Register to comment.