60 Second Countdown Timer with 7 Segment Display using 40110s

Discussion in 'The Projects Forum' started by Sirene Capp, Nov 21, 2018.

  1. Sirene Capp

    Thread Starter New Member

    Nov 21, 2018
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    I'm trying to design the circuit for a timer that counts down from 60-0. I'm using two 40110s connected to two seven segment displays. I plan on using a 555 timer to generate 1Hz pulse to count as my seconds. I'm unsure of how to use the 40110s correctly. I read the datasheet, but I'm unclear on how they function in terms of the inputs (toggle, latch, borrow, carry, etc). I need to count down and set off a "sound" at zero, and then reset. Any help would be much appreciated!

    I don't need to use the 40110s if there's a better way to do this.
     
    LesJones likes this.
  2. MrChips

    Moderator

    Oct 2, 2009
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    Welcome to AAC!

    First of all, what type of 7-segment displays do you have?
    These require common-cathode displays.
    Also you will need seven 470Ω to 1kΩ resistors to connect to the display segments.

    The data sheet will show how to cascade the two counters:

    Connect CARRY (pin-10) from the units chip to CLOCK UP (pin-9) of the tens chip.
    Connect BORROW (pin-11) from the units chip to CLOCK DOWN (pin-7) of the tens chip.

    Look at the truth table for all the other pins.
    i.e. connect LATCH ENABLE, /TOGGLE ENABLE, RESET to Vss (GND).
     
  3. LesJones

    Well-Known Member

    Jan 8, 2017
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    One problem with the 40110 IC is that it does not have a parallel load facility which you would need for the 10s of second stage. You would need to be able to preset this to a value of 6 at the start of the countdown. You could use it for the units of seconds as it has a reset pint to set it to a count of zero.

    Les.
     
  4. Sirene Capp

    Thread Starter New Member

    Nov 21, 2018
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    1
    MrChips - Thanks! I'm such a beginner and this site has so much info! This is just a hypothetical circuit. I did read that they use common cathode displays. Good to know about the resistors. To limit the current to the display, I assume? I was wondering if I could just connect those all to ground, hah.

    Les - Ah, so you're saying I couldn't set the 10s place to 6, but only the 1s place to zero? So I could only use it for the 1s place and would need a different chip that can start at 6. What would you recommend using instead?
     
  5. LesJones

    Well-Known Member

    Jan 8, 2017
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    I can't find a combined counter/decoder that can be preset. A 4029 counter together with a 45117 segment decoder/latch/driver should do what you want. You will also need other ICs to decode the zero zero state to trigger the buzzer.

    Les.
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    There are chips with counter/decoder/driver all in one. I would have to look them up.
    You can use 74HC190 or 74HC192 as UP/DOWN counters and connect them to CD4511 decoder/driver.
    These can interface to common cathode displays.
     
  7. Sirene Capp

    Thread Starter New Member

    Nov 21, 2018
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    1
    Thanks, guys! I've ended up switching to using 74HC190 as an up/down counter and 74LS48D as my decoder (just because it's available in Multisim). So for the 74HC190, since I'm only using it to count down I see I need LOAD and D/U set to high, and CTEN set low. I should use the RCO output from the tens chip as the CLK for the units chip, correct?

    I've never used presetting so let me check that I'm thinking about this right. So I set A, B, C, D of the unit chip to zero aka ground/low, and those inputs of the tens chip to 6 in binary aka A= low, B=high, C=high, D=low?

    Do I need to do anything to reset them to 60 after reaching zero or will they continue to cycle?
     
  8. MrChips

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    Oct 2, 2009
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    General practice says that you must not mix 74HC chips with 74LS chips. The two are designed with completely different technology.
    If you are just doing a simulation then that should be ok for now.

    For actual construction, choose one technology and stick with it.
     
    Sirene Capp likes this.
  9. Sirene Capp

    Thread Starter New Member

    Nov 21, 2018
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    Oops, that was a typo on my part. I am using 74LS190 chips not 74HC. I had no idea what those letters meant, but some googling later, I can see the importance!
     
  10. MrChips

    Moderator

    Oct 2, 2009
    19,143
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    You have to learn to read the fine print, i.e. the data sheets.

    74xx47 are active low ouputs, i.e. use common anode LED displays
    SN7447 outputs can sink 40mA
    SN74LS47 can sink 24mA

    74xx48 are active high outputs. They have internal 2kΩ pull-up resistors. Hence the active current capability is limited.

    You would be better to use 74LS47, 470Ω resistors and common anode LED displays if you want bright displays.
     
    Sirene Capp likes this.
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