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need help with my game show buzzer.

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conconn

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everybody. can you help me with this? i have to know the reason why whenever i push the button on one of the bistable units the other NE555's won't trigger. also, how does pushing the button trigger my 555? i tried to use my "analytic skills" but i'm new to this and only got very few experience. your answers would be of great help. thanks!

**broken link removed**
 
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That is by design. Note at each 555 output there is a resistor in series with a LED to indicate that 555 was triggered. Also note the position of the 1N4148 diodes. What happens to the trigger line when any of the 555 outputs goes high and illuminates its LED? After one 555 has been triggers the ability to trigger another is "locked out" till a reset happens. Again, pay attention to the action of the 4148 diodes and what they do.

Ron
 
what does happen if the output goes high? all i get is that it reverses the other 1N4148's but i can't quite get why it doesn't illuminate my LED. another thing, how does pushing the button trigger my 555?
 
and what is the importance of the resistor before the LED?

To keep the magic smoke in.

Look up the average operating voltage and current of a led, then figure out how it can be operated of a much higher supply voltage.
 
To keep the magic smoke in.

Look up the average operating voltage and current of a led, then figure out how it can be operated of a much higher supply voltage.

oh, thanks. i still have a lot of questions concerning my circuit though. it gives me headache sometimes.
 
When you look at a circuit like the one you have you need to understand what is behind the design. It is a typical game show type circuit where once a contestant hits their button all other contestant's buttons are locked out. The "Reset Line" is common to all the chips (contestant stations). That line is always held high through a 1 K Ohm resistor. Only when a master reset button is pressed do all stations reset and the outputs of all the 555 chips (pin 3) go to a logic low level. Since it is apparent you are not really savvy with a 555 chip configured as a bi-stable multivibrator we will keep this simple. Bi-Stable just means the output can have two (Bi) stable states (On or Off). With all outputs low or off following a reset any chip is waiting for a trigger to make it's output high (On). The way we toggle a bi-stable 555 circuit is to apply a quick logic low to the trigger pin (pin 2). When any contestant bangs their button the 555 is triggered. It only takes a quick momentary bang on their normally open button. When any button is pressed the 555 chip on that button will immediately have it's output go high (turn on) and it will remain in that state. The beeper or buzzer is common to all chips so the buzzer will sound but only the LED for the first chip triggered will light. When this happens the trigger line is pulled high through the 1N4148 diode and once that line is pulled high then any trigger button presses for the other chips will not work. Sort of first come first served. :) Trying to trigger additional chips pressing the trigger buttons will do nothing. Everything remains that way till a reset command resets the chip with the On output. The other chips will ignore that reset.

Ron
 
thank you. i understand a lot better now. so you're saying that the current flowing through the 1N4148 diode is greater than the current flowing down from other bistables when the other buttons are pushed which kinda gives the pin 2 a relatively high voltage? enlighten me please.
 
What I was saying is that once any of the 555 units goes high it pulls the trigger line high. When that happens no other unit can be triggered. The diodes serve as blocking diodes.

Ron
 
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