need help explaining how my circuit works.

Discussion in 'The Projects Forum' started by aleminio, May 8, 2007.

  1. aleminio

    Thread Starter New Member

    May 8, 2007
    4
    0
    I have the following circuit
    http://img412.imageshack.us/img412/6742/vffml7.jpg
    the receiver is connected to the computer, the software randomly lights up 7 leds when you press the switch on the transmitter.

    but i need cpecific details about how the circuit works.
    i mean, what the 555,324,74hct244 do and the like .

    thanks a lot.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Well, the 555 oscillator seems to flash a LED that is picked up by another LED and amplified by the LM324 op amp stages. The pulses are fed into a computer's parallel port, whereupon the program causes the other LED's to be lit.

    All the devices have data sheets available. This looks like a great opportunity to begin your education with rspect to electronics. What goes on in the computer will remain a mystery, though.
     
  3. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    The LM555 is a timer and is used in the astable configuration there. Its only purpose is to flash a LED (this specific circuit seems to be separated from the rest).
    The LM324 is a operational amplifier (pack of 4) (I prefer these instead of using LM741). Both first and second have negative feedback. It seems the first is being used as an amplifier, and the second as a voltage follower. The third is being used as comparator (as far as I can tell), so the output will be digital. The 74HCT244 is a tristate buffer, and it is used to drive the LED's throught the paralel computer port.
     
  4. aleminio

    Thread Starter New Member

    May 8, 2007
    4
    0
    thanks for your help.

    there is something i don't understand, if 555 is a timer, what does it suppost to delay in this circuit? all the transmitter does is sending a signal to activate the receiver, isn't it?
     
  5. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    By the way i see it, the timer does not do absolutely nothing, since it is connected to no other parts except the LED. I can't figure why the timer is there if not as "On" indicator.
     
  6. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    Well from what I can see..... It looks like the first stage of the LM324 is a pre-amp / cpmparator, the second stage is just a buffer that feeds an R,C filter so that the system only responds to a certain extent to what the 555 transmitter sends. The last stage is a comparator.Daniel.
     
  7. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    The 555 timer drives an IR Led that goes to the photo diode input of the comparator circuit. It is essentially creating a pseudo-random time constant that comes out of pin-11 on the DB25 connector.
     
  8. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    It is interesting that the switch is used to connect power to the LM555 for as long as it is pressed. Then upon release the LM555 is no longer powered.

    I guess this is the pseudo-random aspect of the clock source. It is interesting that the LM555 is powered by 9V. It is as though it is a hand-held device that is used to activate the dice simulation over the IR link remotely.

    hgmjr
     
  9. aleminio

    Thread Starter New Member

    May 8, 2007
    4
    0
    well lol i am a little confused, what i have is this circuit split into 5 pieces.
    the 555 transmitter, each of the lm325 stages and the last part, what i need is to explain what each part does or how it works.
    English isn't my native tongue therefore i am trying but can't really understand sentences like
    "pseudo-random aspect of the clock source"


    (by the way, what does H.P.F and L.P.F mean?)
    i have a rectangular integration and it says
    photo diode ->H.P.F -> amplifier -> buffer- >L.P.F -> comprarator

    i also don't understand why do i need a comprarator here.
     
  10. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    H.P.F. stands for high pass filter
    L.P.F. stands for low pass filter


    Pseudo-random is used to describe a random number that is created using a digital circuit or software. It is referred to as pseudo because even though it is a random sequence of numbers, this random sequence can be repeated over and over again by beginning with the same "seed" number.

    Now that I think about it, if there is any pseudo randomness to this circuit it is most likely contained in the software program.

    The LM555 is used to generate a clock source in such a way that the number of clock cycles is not predictable. That is done to insure that the outcome of each roll of the dice is unpredictable.

    hgmjr
     
  11. aleminio

    Thread Starter New Member

    May 8, 2007
    4
    0
    ok thank you
    and yes, the software picks the number.

    Now i just don't get it, why do i need all this stuff if all i need is sending any signal to the leg 11 of the connector.
    to activate the software which does all the work
     
  12. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    You don't need all that stuff. You don't even need pin 11. You could just write software to generate psuedorandom numbers.

    But...

    If you want a remote controlled set-up which lights up external LEDs, you do need all that stuff.

    Another way of looking at it: why do you need the computer? Why not just drive a ring counter with the LM324 o/p?
     
  13. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Greetings Aleminio,

    Here is my attempt at an explanation of the dice rolling circuit you posted.

    I hope it gives a little more insight into the basic function of the circuit.

    hgmjr
     
  14. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    hgmjr,

    There was an error opening your attachment ... It could be me since I've tried it twice.
     
  15. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I don't seem to have a problem opening it. Try right-clicking on the filename and using the "save target as" onto your local machine to see if that will work for you. If you continue to have a problem, pm me and I will gladly email you a copy of the write-up.

    hgmjr
     
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