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Please help modified a circuit

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by cannibal, Sep 27, 2007.

  1. cannibal

    cannibal New Member

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    Thanks, I will test and write the results here :)
     

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    Last edited: Oct 25, 2007
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    If somebody blocks the light from hitting a photo-transistor then the 555 will not time-out and the beeper will make a noise continuously.
     
  3. ljcox

    ljcox Well-Known Member

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    Pin 14 of U1 should go to pin 3 of IC1, not pin 2.

    Also, do you realise that if one LDR is in the dark, the 555 will not be triggered if the light changes on the other one.
     
  4. dave

    Dave New Member

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  5. cannibal

    cannibal New Member

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    I am ok with that
    but if there is a way to solve that then it's ok too to get the idea



     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    We showed you a few weeks ago to use a series capacitor to couple a short pulse from the collectors of the transistors to pin 2 of the 555 to trigger it. Then if something blocks the light the buzzer will beep until the 555 times out.

    Pin 14 of the 74LS90 counter needs to have a low-going pulse as its clock signal. The signal feeding pin 2 of the 555 is low-going.
    Pin 3 of the 555 goes high when the 555 is triggered and goes low when it times out. If pin 3 of the 555 is connected to pin 14 of the counter then the count will advance when the 555 times out.
     
  7. ljcox

    ljcox Well-Known Member

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    The number on the display will not disappear if you connect Pin 14 of U1 to Pin 3 of the 555.
    As audioguru said, the number will increment at the end of the 555 pulse.

    The signal at pin 2 is too slow to trigger the counter (unless there is an internal Schmitt Trigger in it)
     
  8. matk95

    matk95 Member

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    if the 4026 is not avilible in your county then try using cmos 4029 and 4511 to make the counter
     
  9. ljcox

    ljcox Well-Known Member

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    cannibal,
    Do you know that some manufacturers sell the 4000 series CMOS devices with MC1 in front of the 4000 series number?

    For example, the 4026 would be a MC14026, the 4029 - MC14029, etc.

    Note that the 4511 (MC14511) has active high outputs and so it can only drive common cathode LED displays.

    The 7447 has active low outputs so it can only drive common anode LED displays.

    However, the 4534 (MC14543) can be configured for active high or active low, so it can drive both types of LED display. It has a "phase" pin which is set either high or low depending on which option you want.
     
  10. Hero999

    Hero999 Banned

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    Motorola I believe.

    Anyway, the real way of doing this sort of thing is to use a microcontroller, no one bothers with logic gates anymore and this is why they are hard to get hold of.
     
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Digikey has 874 CD4026 ICs (Texas Instruments) in the DIP package in stock today for $.75US each. They have thousands of surface-mount ones in stock today. Somebody must be using them.
     
  12. Hero999

    Hero999 Banned

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    The mind boggles, why do people use them?

    It must work out cheaper in some low production run designs to not use programmable chips.
     
  13. ljcox

    ljcox Well-Known Member

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    Some people may not want to use a microcontroller, either because they want to learn about digital logic or because they are daunted by micros.

    Besides, in some cases, a micro can't do the job.

    I'm currently doing a design for myself in which I'm using 4 PICs and several digital ICs since the PICs are not fast enough to do some functions.
     
  14. cannibal

    cannibal New Member

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    Hello again

    I tested the circuit in breadboard

    I am facing this problem

    When connecting pin 14 of U1 to pin 2 of 555
    the counter only shows zero and not changing also I found that the LDR should be in very dark place so the buzzer get activated

    That’s why I decided to connect pin 14 of U1 to pin 3 of the 555
    and the lDR is working fine and the sensitivity is perfect
    but facing this problem
    the counter starts from 0 zero and when the buzzer stop making sound
    it shows 1 wow it counts

    But here what will happen :(
    when the buzzer activated again and stops the counter return to Zero !!!!

    so it's like this

    zero one zero one zero one

    how can I make it counts zero one two three ....... and so on !!!
     

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  15. ljcox

    ljcox Well-Known Member

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    Please re-read this post by Audio.

    The 555 needs a pulse to trigger it.
     
  16. ljcox

    ljcox Well-Known Member

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    I cannot see any bypass capacitors. You need 100 nF ceramic capacitors across the 555 (pins 4 & 1) and the U1 pins 5 & 10. I think I told you this in a previous post.

    I think the reason why the counter is going from 0 - 1 - 0 - 1, etc. is because of the lack of bypass capacitors and your reset circuit (C5, R9, D2). I suspect that spikes on the +5 Volt line (due to a lack of bypassing) are causing the counter to reset via C5.
     
    Last edited: Oct 28, 2007
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The transistors are nearly overloaded by the very high input current of the old TTL counter IC. Then the gain of the transistors is very low.
    When the input of the counter is removed from the outputs of the transistors then they are much more sensistive to reduced light from darkness coming.

    Another reason to use a CD4026 Cmos counter IC. It has NO input current.
     
  18. cannibal

    cannibal New Member

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    Ljcox

    I used the bypassing capacitors in my breadboard us you said
    and the problem is still

    also I tried to remove the reset circuit (C5, R9, D2) and when the power on
    I get 8 then after buzzer stop I get 9 then

    8 ,9 ,8 ,9 ,8 ,9 like that

    I am tired from this old TTL IC's but I can't find CD4026 in Oman
     
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Connect the reset pins to ground then the counter will not reset and will count.
    If the display number keeps changing then maybe the LDR is seeing a mains-powered flickering light and then maybe the counter is counting the flickering.
    Then the 555 will also be triggered over and over.

    Breadboards have loose connections and too much capacitance between wires for high speed TTL ICs. Use strip-board or a pcb.
     
  20. cannibal

    cannibal New Member

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    I connected the reset pins to ground and it's true that it dosen't reset but it's also not counting only switching between two numbers
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The output of the LDR and transistor might be to slow to clock a high-speed TTL counter. Then a Schmitt-trigger circuit is needed to feed the counter.
     

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