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Cmos and TTL

Discussion in 'General Electronics Discussion' started by ForceMaster, Jan 18, 2012.

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  1. ForceMaster

    ForceMaster

    19
    0
    Jan 11, 2012
    Hi,
    Does this circiut work,

    From counter 7490 to 4081 the outout from 4081 is allways low, when one input is LOW
    When the 4017 counter lights up , it will then "open up" 4081, by going HIGH.
    then output will then flow to 4543 i hope ??
    and when 4017 count more, it will make the fist 4081 LOW and another HIGH, and then the output from next 7490 will be shown in 4543 , am i correct ???

    Rgds
    ForceMaster
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,319
    2,595
    Nov 17, 2011
    Could you supply a more detailed schematic? Which pins are connected in what manner? From your sketch it would be hard work to find out what the circuit would do.

    What is the supposed function of the circuit?

    Harald
     
  3. ForceMaster

    ForceMaster

    19
    0
    Jan 11, 2012
    Hi

    Part1.jpg.
    The readout from 2 counters, can be selecet one at a time, be feeding the 4017 with a input. 4017 will then change from first to second counter.
    is that possible ?

    part2.jpg
    have a different counter, that will be reset every midnigt, at then "data" from the counter will be shiftet from one 7475 to the next ( 7 pcs.)
    read where the readouts will be.
    is that possible, ?

    Hope you better can understand it now.
    for better clarity i only show one bit of the counters.

    Rgds
    ForceMaster
     

    Attached Files:

  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,482
    2,830
    Jan 21, 2010
    TTL driving CMOS is not really a good idea.

    The "high" level for TTL is not really high enough for CMOS.

    either use CMOS throughout, or use 74HCT CMOS (which has TTL compatible inputs) or use pull-up resistors.

    Using a 4017 to select between one of 2 devices is really wasteful. Can't you just connect an inverter between the pair of enable pin (sets) and use a simple logig high/low to select one set or the other?

    edit: the bottom of page 3 and the top of page 4 are relevant. And page 8 of this. Since your TTL is *only* driving CMOS, you'll probably be OK. But why not use a 74HC90 and eliminate the problem (as well as a large amount of supply current).
     
    Last edited: Jan 19, 2012
  5. ForceMaster

    ForceMaster

    19
    0
    Jan 11, 2012

    Sure i can use 74HC, but as you wrote , as long as just driwing the cmos .
    yes i could skip the 4017, but i have only written a part of the schematic, i will have 8 different to choose between., and just one button to select with.
    Should over 4 volt not be enough for a cmos 4081 input ?
    And what do you mean by using pull up risistor ?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,482
    2,830
    Jan 21, 2010
    OK, if there's 8, you need to connect the 9th output to the reset pin of the 4017. And your schematic should show the other outputs labelled as being used. It helps communicate stuff.

    A pull-up resistor is merely a resistor connected between the output and V+.

    The documents I pointed you to would tell you if 4V is enough. But a rule of thumb for CMOS is 1/3 and 2/3 Vcc, so lower than 1.7 volts for low and higher than 3.3 volts for high.

    TTL can be as low as 2.8V for a high logic level (albeit when loaded by other TTL inputs), so that's where the problem is.

    I hope you're debouncing your selector button.
     
  7. ForceMaster

    ForceMaster

    19
    0
    Jan 11, 2012
    I will upload a much better schematic tonight.

    rgds
    ForceMaster
     
  8. ForceMaster

    ForceMaster

    19
    0
    Jan 11, 2012
    Hi again,
    Here you have it.
    It will be used to counts the rain every day.
    i have a clock, a counter total, and a day counter.
    I will have the possibility to se 7 days bagwards. ( 7475 )
    from left you have the day counter, and in top the readout display.
    for make it easy to understand, i have only put A and B for 1 digit.
    when midnight arrives, one 4017 counter can count, and the last 7475 can get new input, and "lock" and the next ect, so that the data is shiftet from day -6 to -7 and from day -5 to day -6 ect.

    The other 4017 is used for selecting readouts from everyday "stored" in 7475,

    i think it will work, but you er concerend about the "high" status of 7490, but you think i should use a 10kohm risistor as pull UP. ? just from 7490 or also from 7475 ?

    Maybe it can be done a different way.

    Rgds
    ForceMaster
     

    Attached Files:

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