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Blinking LED 555 Timer

  1. Dec 20, 2012 #1
    Hi guys, I figured I might try making a LED to phase on and off for around 1 second, to be perfectly honest I have NO idea what I'm doing really. But figured thats the best way to learn right :P. So I'm using a Timer 556 and connected it in a way that kind of made sense from the 555 IC timer wikipedia webpage. I created a schematic, but was wondering whether someone would mind checking it? is it right? is it wrong? is there any method to my madness, or am I just being silly connecting random stuff together haha. It will be very much appreciated,

    I haven't looked into too many other circuits (read: I didn't use search to find someone elses thread) of the same type as I'm trying to go about it more by myself then just copying someone else's circuit, I know that makes it easier to learn but I find I learn better when I just kinda try things :P. But yeah cheers!!


    Schem_Blink.jpg
     
  2. jcsd
  3. Dec 20, 2012 #2
    I know nothing, but pin 1 should be ground, pin8 is VCC +4.5-15V, I know there's a load of ways to hook them up, I don't know
     
  4. Dec 20, 2012 #3
    Really? I'm a bit confused about the pins especially the trigger :(, I did notice there was heaps of ways to hook them up as well. I'm hoping what I want is a monostable timer, just to give the impression of being high for 1 second then low for 1 second. I'm also putting VCC to 5V so hopefully its enough, it seems to be in your range that you stated :D
     
  5. Dec 20, 2012 #4
    Since your trigger pin is connected directly to ground( Trigger pin is the Negative terminal input to the comparator whose positive terminal is at Vcc/3 Volts, so In this comparator the positive terminal is always greater than the negative terminal so this comparator output is always 1 , this is connected to S terminal of rs flip flop whose o/p is IC output ....so you 'll get high output always...so your LED will always be on I guess.
     

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  6. Dec 20, 2012 #5
    Oh right, that makes sense, I was confused with the trigger part as I didn't really understand it too much from the wiki page. Would that mean i should connect it to VCC? I just saw your schematic now, is that the inside of a 555 timer? Since it looks really interesting, I've seen a bit about how flipflops work, so I might try going over mine again using the logic from your schematic.
    Cheers
     
  7. Dec 21, 2012 #6
    That is not the complete schematic of Timer IC, [I've not shown another comparator whose one input is threshold pin and a discharge logic using transistor]

    [If you connect trigger pin to Vcc the negative terminal of that comparator will always be higher than positive terminal so its o/p will always be low and so is the set input of flip-flop, then you cannot set the flip-flop which makes o/p to be low always ]

    You can make different type of connections to get phase on and off for around 1 second one way is short trigger and threshold and connect it to capacitor and connect other end of cap. to discharge pin. . .and adjust the resistor value (resistor through which cap. charges and discharges) to get 1 sec on and off time. . .

    PS. study the complete Internal structure of timer once, Then you can make all kinds of stuff using timer very easily
     
  8. Dec 21, 2012 #7
    Thanks so much for all your info mate, just found a page now explaining even more about the timer, and showing me the short between the trigger and threshold. From what I can gather I wanted the timer set as an astable and not monostable which I guess I should of guessed from the title of the circuit haha. But it did push me into looking more into the timer and how its built inside and the logic involved. I'm hoping to be able to remake the circuit with the info you've given me hopefully tomorrow. Just another question, in the monostable circuit I was under the impression that the

    time=ln(3)R*C

    But in the Astable circuit there is two resistors, plus the capacitor, so is the time variable still the same (albeit with R1+R2), or is it only dependent on one resistor??
    Here is the site I'm going off of http://www.555-timer-circuits.com/flashing-led.html
    Cheers heaps!!
     
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