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The Learning Circuit
Documents 555 Timers - How Bistable Mode Works -- The Learning Circuit 70
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  • Author Author: tariq.ahmad
  • Date Created: 14 Apr 2020 7:08 PM Date Created
  • Last Updated Last Updated: 8 Jan 2020 8:24 AM
  • Views 4443 views
  • Likes 8 likes
  • Comments 13 comments
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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

 

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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

 



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Top Comments

  • jw0752
    jw0752 over 5 years ago in reply to fmilburn +5
    Hi Frank, I couldn't find my schematic of the two different circuits until just now. Here is what they look like. John
  • jw0752
    jw0752 over 5 years ago in reply to fmilburn +2
    Hi Frank, I don't know if they never got properly inserted or what. I can't edit the original post so I will insert the pictures here. The pictures add a little color but are probably irrelevant as they…
  • makerkaren
    makerkaren over 5 years ago in reply to aswinvenu +2
    Yeah, since I've made so many videos about 555 timers, I was trying to not repeat myself too much. Looking back there are a few times I should have kept in details such as this. Those editing choices get…
  • miles90
    miles90 over 4 years ago in reply to makerkaren

    Thank you.

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  • makerkaren
    makerkaren over 4 years ago in reply to miles90

    Yay! You are very welcome.

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  • miles90
    miles90 over 4 years ago

    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.

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  • jw0752
    jw0752 over 5 years ago in reply to beacon_dave

    Hi Dave,

    You are right. I must have tried to edit out of the mail box window. When I bring up the full thread the edit option is there.

    John

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  • beacon_dave
    beacon_dave over 5 years ago in reply to jw0752

    "...I can't edit the original post..."

     

    If you were still inside your 'Inbox' when you tried to edit, then it doesn't usually give you the option to do so.

     

    Instead if you click on the main document title, or your comment timestamp (e.g. '2 Months')

    https://www.element14.com/community/docs/DOC-94845#comment-256064

    to open the document outside of your Inbox, then it should then give you an Actions option, under which there is the Edit option.

     

    However you may have found another anomaly... image

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  • jw0752
    jw0752 over 5 years ago in reply to fmilburn

    Hi Frank,

     

    I couldn't find my schematic of the two different circuits until just now. Here is what they look like.

     

    image

    John

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  • makerkaren
    makerkaren over 5 years ago in reply to aswinvenu

    Yeah, since I've made so many videos about 555 timers, I was trying to not repeat myself too much. Looking back there are a few times I should have kept in details such as this. Those editing choices get difficult when trying to keep the videos under 10 minutes.

    Thanks for the feedback!

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  • aswinvenu
    aswinvenu over 5 years ago

    Really great video. It would have been complete if you can talk about the RS flip-flop inside the 555 timer.

    I fear that people may get confused why the output state is preserved even if you release the button. If it's just comparator then as soon as you release the button it should flip the state back.

     

    Regards,

    Aswin

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  • fmilburn
    fmilburn over 5 years ago in reply to jw0752

    Thanks John,

     

    I wasn't aware there were two methods and just wanted to make sure I am not missing something else :-).  They do show how neat your work is, even on a breadboard.

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  • jw0752
    jw0752 over 5 years ago in reply to fmilburn

    Hi Frank,

     

    I don't know if they never got properly inserted or what. I can't edit the original post so I will insert the pictures here.

     

    image

     

    image

     

    image

     

    The pictures add a little color but are probably irrelevant as they don't really show much.

     

    John

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