555 timer bistable mode – Flip flip basic circuit

Bistable mode, also called flip flop, 555 timers hold their output (pin 3) either high or low depending on which input, trigger (pin 2) or reset (pin 4 ) was last given a low signal.



Assortment of commonly used integrated circuits (IC). I made a lot of videos with them

Schematic

Bistable 555 timer circuit schematic dagram by electronzap electronzapdotcom
Bistable 555 timer circuit schematic dagram by electronzap electronzapdotcom

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Circuit description



White version of the oscilloscope that I use in many of my recent videos.

  • Trigger pin (called set pin in this circuit) with a low signal sets the output high. Unless the reset pin also has a low signal, in which case output stays low.
  • Reset pin sets the output low no matter what, as long as it is pressed. after it is released, the output stays low until there is a low signal to the trigger/set pin.
Pull up resistor example circuit schematic diagram by electronzap electronzapdotcom
Pull up resistor example circuit schematic diagram by electronzap electronzapdotcom
  • Pull up resistors hold the set/reset inputs high (Vcc) until a direct connection to 0V is made. Don’t leave input pins floating, they will pick up weak electromagnetic signals that surround them.
  • Output LED headed to ground lights up when the output is high.  High output voltage is however close to the positive supply voltage that the 555 outputs.
  • Output LED headed to the positive supply (Vcc, 5V, etc.) lights when the output is low. Low 555 output is almost connecting directly the 0V/negative supply rail voltage.

Video



Power supply I use in my videos.
555 timer bistable flip flop mode basic circuit with alternating LEDs electronics by electronzap

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