Mux and counter

Discussion in 'General Electronics Chat' started by newbies_hobbyist, Jun 4, 2010.

  1. newbies_hobbyist

    Thread Starter Member

    Jun 4, 2010
    67
    8
    Hi Experts,

    I really need your help for the circuit I want to make. I want to make a mux circuit with counter to count the 24 switch. I want to use 74ls450 16:1 mux with two outputs "Y" as the true out and "W" as inverted out to accomodate the 24 switching. Well it goes like this, mux will switch from 1-16 (Y out) with 5 seconds delay interval switching and then after it switch to switch 16 i want to disable it and enable the W out to continue the remaining 8 switch to complete the 24 switching and this can be obtained by putting two mosfet, one for "Y" and one for "W". Of course I need 555 as timer and a counter but I don't know how to do it. Please see my attachment.

    Thanks
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You only need eight extra inputs. A 74LS 151 is an eight input multiplexer. It has an enable pin that can be used to turn it off with some external logic.
     
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  3. newbies_hobbyist

    Thread Starter Member

    Jun 4, 2010
    67
    8
    Do I really nees a software to make it work? We'll I just want it just pure hardware. I know this will work with just hardware by using 555 and bcd counter, if my understanding is right. Thanks for the reply
     
  4. newbies_hobbyist

    Thread Starter Member

    Jun 4, 2010
    67
    8

    About 74ls151, it is just only 8 switch but I need 24 switch which is I believe that 74ls450 can manage to do that because it is 16:1 mux plus it has 2 out which is "Y" as the true out and "W" as the inverted. By using the two out I can manage to have 24 switch.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    282
    Perhaps I do not follow your circuit function. My suggestion for the 'LS151 was to add 8 additional lines to the 'LS450's 16, for a total of 24 lines that could be multiplexed. Some additional gates will be necessary to control which of the multiplexers is selected. You have indicated nothing about the counter or a control (if any) on the LM555.
     
  6. newbies_hobbyist

    Thread Starter Member

    Jun 4, 2010
    67
    8
    Well I think i'm getting it little by little. I will use 555 as timer (4pcs) for each control pins (A, B, C, D) which will dictate my 16 switch positions that has 5 seconds interval in every switch. Then I will use one more 555 timer that can either disable the mosfet which is connected to "Y" out or disabling the Vcc supply for 74ls450 by adding transistor and the control is in 555 timer that will give an 80 seconds lo-hi/hi-lo signal with 50% duty cycle. Then I can use 74ls151 as a second mux to get the remaining 8 switch to complete the 24 switching. Now I need to figure out how to use a counter with this circuit. I want my counter to count the 24 switching and I believe the total time Check out the new drawing maybe you can help me. The circuit is still not complete (counter is not yet included). It's like a puzzle to me to build the whole circuit. All of the timer will work in 50% duty cycle.

    Thanks,
    Mike
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    That is a start, but very incomplete.

    The LM555 is probably good as a clock source, but using one to clock a set of counters to go from 0 - 23 is going to be much simpler than arranging four 555's to stay sync'ed. Use a 'LS163', as an external AND gate like a 'LS08 can detect a count of 8 plus the clock to reset the counter to 0.

    You can use the full count out of the '163 to run the '450 multiplexer - 16 counts, 16 channels. When the TC goes high, disable the '450 and apply the count to the '151.

    I'm pressed for time today, so if you need some help with the logic, be patient.

    When you say "count the 24 switch", do you mean to scan the switches to see their states (open = HIGH, closed = LOW)?
     
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