Timer and Relay

Discussion in 'The Projects Forum' started by stryker23, Apr 15, 2009.

  1. stryker23

    Thread Starter Member

    Apr 15, 2009
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    I'm working on building a circuit that will be powered by a 6.3 volt sinusoidal source. I need to convert the sine wave to a square pulse in order to connect it to a counter that will be connected to a seven segment display. I want the display to count to 8 and then trigger a relay to power an led.

    I'm trying to simulate the circuit in PSpice before building it, and I'm stuck trying to convert the input. After searching on here I believe I can do it with a comparator circuit, but I'm not sure how to calculate the resistor value and what is the value of Vref? Next, what is the best way to control the frequency in order for the counter to change every second? On a side note, I tried looking a schmitt triggers first because it seemed like they could be used to control the frequency and the conversion of the sine wave. Would a schmitt trigger work better? Both circuits seem very similar. Any help would be appreciated. I've been looking for awhile and haven't been able to figure any of this out. I'm attaching a simple block diagram. I'm not sure about the dividing by 60 part.
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What kind of chips do you use for the counters?
    Are they 74XX series or 40XX series?
    Knowing the value of the powersupully you are going to use I can try to draw something.

    [​IMG]

    I am using a schmidt-trigger nand gate for pulse-shaping.

    Greetings,
    Bertus
     
    Last edited: Apr 15, 2009
  3. stryker23

    Thread Starter Member

    Apr 15, 2009
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    I'm using 7400 chips. What else do you need to know about the power supply?

    Thanks
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    How do you intend to make the power supply?
    Are you going to use a rectifierbridge, buffer capacitor and regulator?

    Greetings,
    Bertus
     
  5. stryker23

    Thread Starter Member

    Apr 15, 2009
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    Im not planning on building the power supply. I was just planning on connecting a 6.3 volt sine input to test the function of the circuit.
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In that case you can connect the 6.3 Volts AC to the circuit I gave you.
    The diodes will protect the input of the IC.
    For safety you can put a 1K resistor in series with the inputcapacitor.

    Greetings,
    Bertus
     
  7. stryker23

    Thread Starter Member

    Apr 15, 2009
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    Ok, in your diagram what are the 4k7?

    Thanks
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    That are two resistors to keep the DC at the input of the gate at about 1/2 Vcc.

    Greetings,
    Bertus
     
  9. stryker23

    Thread Starter Member

    Apr 15, 2009
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    Will the output frequency be correct in order to have the display increment each second or will it have to be divided?
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    If your main power has 60 Hz you will need to divide it by 60 to have second pulses.
    This can be done with the divide by 5 part of the 7490 and the both sections of the 7492 (divide by 2 and divide by 6).

    Greetings,
    Bertus
     
  11. stryker23

    Thread Starter Member

    Apr 15, 2009
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    If I connect it to a flip-flop it will decrease by 50%, from what I have found through searching. I can then connect it to multiple flip-flops to get an approximate 1Hz frequency. Is there an easier or more exact way? I'm not familiar with many ICs, but will a divide by six counter be a step in the correct direction? Would that be the equivalent of a 10Hz frequency?
     
  12. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I just added this line to my last post:
    This can be done with the divide by 5 part of the 7490 and the both sections of the 7492 (divide by 2 and divide by 6).

    Greetings,
    Bertus
     
  13. stryker23

    Thread Starter Member

    Apr 15, 2009
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    How do I connect the four outputs of one counter to another counter?
     
  14. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Here is the connection diagram of the 7490 and 7492:

    [​IMG]


    To make a 60 divider you will need to make the following connections:

    7490 pins 2,3,6,7 and 10 connected to GND : pin 5 to Vcc
    Pin 1 (input 5 divider)
    Pin 11 (output 5 divider) to pin 1 7492

    7492 pins 6,7 and 10 connected to ground : pin 5 to Vcc
    From pin 11 7490 to pin 1 (input 6 divider)
    Pin 8 (output 6 divider) to pin 14
    Pin 14 (input 2 divider)
    Pin 12 (output 2 divider) to the counter.

    Greetings,
    Bertus
     
  15. stryker23

    Thread Starter Member

    Apr 15, 2009
    13
    0
    I'm having a problem with the display. It seems to be changing every second, but it counts even and then it counts odd displaying E, L, P, and a - sometimes. It is a LN513RA Seven segment display. I need it to count to 8 and then hold at 8. Any idea what I have wrong. Is one of the IC possibly not working?
     
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