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Discussion in 'The Projects Forum' started by Abdelrahman95, Apr 11, 2015.

  1. Abdelrahman95

    Thread Starter New Member

    Apr 11, 2015
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    Can anyone help me to install counter to count down from 10 to 0 using 555 & 2 of 74192 & 2 of 7447 + 2 seven segment the problem I face is to make tens digit and unit digit as it counts from 10 to 0 so please if anyone can help me.
     
  2. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Sure, show us what you've got so far (schematic).
    Homework? (why else use double decoder/driver/display for a single count more).
     
  3. Abdelrahman95

    Thread Starter New Member

    Apr 11, 2015
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    Here is the Schematic I worked on the problems I face are:
    First the seven segments display 20 or 22 I don't know why this specific numbers and it doesn't change.
    Second when the current go to the 555 timer without the rest of circuit the indicator led works well but when the rest circuit connected with the 555 timer ( pin 3 output) the indicator doesn't work the light is so weak .
    Third I don't know how to make it reset when it reaches 00 ex: 10 09 08 07 06 05 04 03 02 01 00 reset 10 09 and so on .
    I hope you can help me and correct me if I made mistakes.
    Thanks in advance.

    Note : I have attached the schematic circuit.
     
  4. Retiredguy

    Member

    Feb 24, 2007
    28
    5
    First of all, after looking at your circuit, the 74192's will not count unless the CLR inputs are tied low. Second, I do not know what type of chips you are using, but regular TTL chip must be powered from 5 volts not the 9 volts your circuit is showing. If you are using CMOS type chips then you will be OK. Third, you will need resistors between the outputs of the 7447 and your display. About 220 ohm should work. And last, I am not sure that your display type is correct, the 7447 puts out a logic high for each segment to be lit, and what I see from what you posted you have it wired that a logic low will light the segment. Will be gone for a while but will check back.
    Mike
     
  5. Abdelrahman95

    Thread Starter New Member

    Apr 11, 2015
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    Thanks for the point of 9v vcc I search about type of my chips and it works in range from 4.5v to 5.5v for 7447 & from 2v to 6v for 74192 and from 4.5v to 16v for 555 so I deliver 5v to the all circuit not 9v and I connect CLR of both to ground then I test the circuit the result was the led indicator works well but the seven segment still fixed at 20 but there is something wired when I touch first 74192 the display shows various numbers then I remove my hand go back to 20 as it is , I don't know what is the problem note I replace the ics with another and have the same result .
    The second point I want it to count down from 10 and when reach 00 it reset what can I do to fix such problems.
     
  6. Abdelrahman95

    Thread Starter New Member

    Apr 11, 2015
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    The point of 220 ohm it is only for saving 7 segment from damage and doesn't affect the circuit the problem I face why the circuit doesn't work ? what is the wrong ?
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Where are you from Abdelrahman95. Update your profile and add your country.

    Plus change R3 to 220Ω or 330Ω first.
    Second find 4 pcs of 100nf ceramic capacitors. And connect 1 cap to each IC across the IC supply pins. Keep the capacitors as close to IC as possible.
    1 cap for each IC..
    Third do not apply more than 5V to the whole circuit and make sure you supply can handle atleast around 500mA.

    Tell me are you using CA or CC 7 segments
     
  8. Abdelrahman95

    Thread Starter New Member

    Apr 11, 2015
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    First I am not angry & I am sorry for delivering bad impression about myself but I don't mean that.
    Second I am from Egypt.
    Third where is R3 I only use two resistors ( R1 & R2).
    Fourth do you mean by supply lines which is Vcc of each ic or what.
    Fifth I am aleardy suppling 5v to the circuit as I say in reply no #5.
    Finally As the Schematic shows that I connect 7 segment to +9v but now it will be +5v that's mean it is CA 7 segment.
    The question was how I make it works for 10 sec and reset + the problem of working .
    But at the end I will update the circuit as you said and see the difference.
    Thanks in advance.
     
  9. ScottWang

    Moderator

    Aug 23, 2012
    4,857
    767
    You haven't answer the question, is this a homework?
    We have homework forum here and the experts will like to help, if this is the homework, I will move it to the homework forum, and they will not doing the job for you directly, just hope you can learning something from discussion.
     
  10. MrCarlos

    Active Member

    Jan 2, 2010
    400
    134
    Hello Abdelrahman95

    There are some things to improve in your design:

    1)- It is very likely that the Load that represents the LED and Its limiting resistor do not let the 555 raise its output level to an appropriate value for the units counter in order it "feel" a high level; for that reason does not count +1. Or –1 in this case.

    2)- The way we used the 74192 to achieve your purpose is to use the D's inputs to program and input of Control PL (11).
    You have all the inputs D's grounded. This way you can NOT tell the counter to start in this or that number.

    3)- All devices incorporating LED’s require a current limiting resistor. if not add, your circuit may demand more power than needed or could damage those devices with LED's. suddenly or gradually.

    4)- It is not advisable to leave without connecting PIN’s in these circuits.
    you have some without connection.
    Note: I think the type of 7-segment display you use is appropriate for the 7447. Otherwise there would brighten any segment.

    My recommendations:
    1)- increases the value of the resistance connected to the LED on the output(3) of the 555.
    the value of this resistance is calculated as follows: Rx = (VCC - VF) / IF
    VCC, bias voltage of the circuit in question.
    IF, maximum current specified by the manufacturer of the LED. To fully on.
    VF, voltage drop at the terminals of the LED when it is crossed by the IF current.
    Rx, Resistance In Ohms.
    You can also add a transistor to drive the LED. With this you decrease the power load at the output of 555.

    2)- You will Program the inputs D's of the counters to permanently stay the number at which you want to start to count.
    In this case 10(Dec) 1000 0000(Bin).
    Now: Your 2-Digits counter should show the following sequence:
    10 09 08 07 06 05 04 03 02 01 00 99 in this moment you have to reset the counter to 10 to keep counting that sequence. The number 99 will not be visible in the Display's because the change 99 ---> 10 is dramatically faster.

    To achieve this we use the Q's outputs of the counters and its control inputs PL(11). Both PL.
    Now we need to detect, through a gate, when the counter reaches 99(Dec) 1001 1001(bin).
    The output of this gate is connected to the PL(11) inputs of the counters Which are programmed to 10(Dec). 1000 0000(Bin) for their inputs D's.
    What type of gate would use and how many inputs ??

    3)- Calculate the value of current limiting resistors for all segments of all displays. And LED’s have in your design.
    If you do not, you can damage these devices. Suddenly or Gradually.

    4)- PIN’s MR(14), on the counters, if not used must be connected to Ground.
    PIN's LT(3), BI/RBO(4), RBI(5) in 7447 look properly connected.
     
  11. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    This and your post #5 tells me that you're working on a solderless breadboard - you should check for loose connections and such and make sure you don't have long wires going everywhere. Nice and tidy is a must if you work on a crappy solderless breadboard with semi-bad contacts.

    You have set your preload value to 00
    If you want to preload to 10, you need to make pin 15 of the tens counter high.


    Preload to the value 10 (0001) on the tens and (0000) on the units.
    Then wire the "borrow" (pin 13) of the tens counter to the preload (pin 11) of both counters.
    Then it will count 10, 09, 08...02, 01, 00, 10, 09 etc.

    Tie down the CLR (pin 14) of each counter as post #4 says and use 220..330 Ohm resistors on each segment (#4 has got the outputs of the 7447 reversed though - lit segments are low and the display must be a common anode (CA)).

    Your first priority is to get your circuit stable though, or you won't know if anything else you do is right or wrong,

    If random hand sensitivity persists, consider the option of tossing the breadboard and use either Manhattan or Dead-bug mount (either one magnitudes more stable than a solderless board with a bit of use on the clock).


    To sum up connections of the counter-pins...
    Unit counter:
    Pin
    1 gnd
    2 to 7447 #1
    3 to 7447 #1
    4 counter pulses from the 555
    5 +5V
    6 to 7447 #1
    7 to 7447 #1
    8 gnd
    9 gnd
    10 gnd
    11 to pin 11 and 13 on tens counter
    12 n.c.
    13 to pin 4 on tens counter
    14 gnd
    15 gnd
    16 +5V

    Tens counter
    Pin
    1 gnd
    2 to 7447 #2
    3 to 7447 #2
    4 to pin 13 on unit countwer
    5 +5V
    6 to 7447 #2
    7 to 7447 #2
    8 gnd
    9 gnd
    10 gnd
    11 to pin 13 and pin 11 on unit counter
    12 n.c.
    13 to pin 11 on both counters
    14 gnd
    15 +5V
    16 +5V
     
  12. Abdelrahman95

    Thread Starter New Member

    Apr 11, 2015
    7
    0
    It is not a home work. and thanks for explaining.
     
  13. Abdelrahman95

    Thread Starter New Member

    Apr 11, 2015
    7
    0
    How to make counter count down from 10 to 0 then from 5 to 0 then from 10 to 0 and so on.
     
  14. ScottWang

    Moderator

    Aug 23, 2012
    4,857
    767
    If you have not buy the components then I will suggest you to use CD4510 and CD4511.
     
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