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555 Timers - How Bistable Mode Works -- The Learning Circuit 70

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555 Timers - How Bistable Mode Works

The Learning Circuit | element14 presents |  Project Videos

 

 

Karen has been digging into 555 timers for a bit now. In a previous video, she did an overview of the 3 different modes in which a 555 timer can be used. In this video, Karen goes into further detail about one of those modes: Bistable. In bistable mode, signals at two inputs are used to manually set the output of the 555 timer high or low. For example, one button could trigger the output to turn a light on, while a second button could reset the output to turn the light off. This video goes over what is happening in the 555 timer internally to make this type of circuit work. Karen also presents a practical example on a breadboard to show using a 555 timer in bistable mode.

 

 

Bill of Material:

 

 

Product Name Manufacturer Quantity Buy KitBuy Kit
Breadboard, MCM 60 rows, ABS, 8.5mm, 165mm x 56mm Multicomp 1 Buy NowBuy Now
LM555CN - Timer, Oscillator & Pulse Generator IC, TTL Compatible, Astable, Monostable, 4.5 V to 16 V, DIP-8 On Semiconductor 1 Buy NowBuy Now
Ceramic Disc Capacitor, 0.01 µF, 100 V, ± 20%, 5 mm Vishay 1 Buy NowBuy Now
140 Pc. Jumper Wire Kit, 22 AWG, Solid, Assorted Lengths and Colors Twin Industries 1 Buy NowBuy Now
Through Hole Resistor, 220 ohm, 400 mW, ± 1% Vishay 1 Buy NowBuy Now
Through Hole Resistor, 1 kohm, 500 mW, ± 1% TT ELECTRONICS / WELWYN 2 Buy NowBuy Now
Red LED, Through Hole, 5mm, 20 mA, 2.1 V LED TECHNOLOGY 1 Buy NowBuy Now
Tactile Switch, 12mm, Yellow, Top Actuated, Through Hole, Round Button, 24 VDC, 50mA Omron 1 Buy NowBuy Now
Tactile Switch, 12mm, Red, 12 VDC, 50mA Multicomp 1 Buy NowBuy Now

 

Additional Parts:

 

Product Name
Desktop Power Supply

 



Parents

  • Thank you Karen.

     

    I could not understand why the output pin stays on when the first button is released. It stays on as long as the threshold pin’s potential is below two thirds of Vcc. So, for example,  it will stay on as long as the threshold pin is connected to ground.

     

    To be honest, I was scared by the details of the 555 timer. But now, thanks to you, this chip looks much less scary to me. You are doing a great job. Thanks again.

Comment

  • Thank you Karen.

     

    I could not understand why the output pin stays on when the first button is released. It stays on as long as the threshold pin’s potential is below two thirds of Vcc. So, for example,  it will stay on as long as the threshold pin is connected to ground.

     

    To be honest, I was scared by the details of the 555 timer. But now, thanks to you, this chip looks much less scary to me. You are doing a great job. Thanks again.

Children