I had recently asked a quiestion here: Will this circuit for quiz buzzers work? and I got this answer.

I am trying to understand the circuit and I have understood most of it but there is only one part that I am not able to understand.

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I don't understand electronics in theory properly so can you explain in simple english why this ground and resistor have been connected?

  • \$\begingroup\$ I think that without that resistors, the tension of the base is not fixed and probably will float when the keys/buttons are open. \$\endgroup\$
    – user41342
    May 4 '14 at 21:52
  • \$\begingroup\$ @Luis What is the meaning of 'tension of base'? \$\endgroup\$
    – Kartik
    May 5 '14 at 0:51

Strictly speaking, they aren't required, but those resistors help speed up the turn-off of the associated transistors, and also help with noise immunity by pulling the base connections all the way to ground when the switches are open.

  • 2
    \$\begingroup\$ The standard term for this configuration is "pull-down resistors". \$\endgroup\$
    – keshlam
    May 5 '14 at 4:37

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