Home     Contact     Projects     Experiments     Circuits     Theory     BLOG     PIC Tutorials     Time for Science     RSS     Terms of services     Privacy policy  
 Home      Projects     Experiments     Circuits     Theory     BLOG     PIC Tutorials     Time for Science   

Bistable relayAuthor
April 2, 2013

Supplied with 12 Volt DC this basic circuit drives a relay by a momentary button. The coil takes about 2,5 Volt when the button is pressed and 5 Volt when the button is released and the transistor conducts. In other words the circuit uses the coil hysteresis.
By pressing the button both transistors conduct but the coil keeps off due to the low voltage.
With released button Q2 transistor keeps on for a short time, while the relay switches on.
By pressing the button again Q1 conducts, discharges the capacitor and causes a power fall on the base of Q2, while the relay keeps on.
Once the button is released Q2 would switch on with a very small delay, because the capacitor has to charge. Since the relay is faster the circuit backs to the start condition.
Unlike the mechanical bistable relay this circuit backs to the start condition when you cut off the power supply.


N.1 relay 5V DC - 125 ohm
N.5 diodes 1N4007
N. 3 resirtors 8,2K
N.1 resistor 18K
N.1 resistor 82
N.1 resistor 180 (0,5W)




  Email (shall not be published)


Notify me of new posts via email

Write your comments below:
BEFORE you post a comment:You are welcome to comment for corrections and suggestions on this page. But if you have questions please use the forum instead to post it. Thank you.


  • At 18 May 2013, 14:44:08 user Cleiton wrote:   [reply @ Cleiton]
    • Hey, thanks for your great projects
      but i cant completely understand the schematics you posted
      and this is different of other projects you have, you
      havent put a list of materials too
      maybe you could update this for our better understandings

      thanks guy, great project!

  • At 9 April 2013, 11:49:57 user Andrea wrote:   [reply @ Andrea]
    • @msnehhumam
      It's a nice solution since it works with basic components and without using the relay contact.
      Basically, if it works with a lamp, then it should also work with a coil.
      Maybe you have to modify the value of some components.

  • At 9 April 2013, 3:56:33 user msnehhumam wrote:   [reply @ msnehhumam]
    • Always exist advantages and disadvantages
      between one and another circuit

      is necessary to verify the possibility that the other
      work with a relay instead of a lamp
      but I think it can work and it seems to be
      something much simple

  • At 3 April 2013, 14:53:17 user Andrea wrote:   [reply @ Andrea]
    • Hi Giorgos
      The circuit is very simple and works fine, but the duration has to be tested. It may fail if the coil response increases due to the long time use of the relay.

  • At 3 April 2013, 5:49:58 user Giorgos Lazaridis wrote:   [reply @ Giorgos Lazaridis]
    • Welcome back! Nice and solid solution.

    reddit this Reddit this

     HOT in heaven!

    NEW in heaven!

    New Theory: AC electric motor working principle

     Contact     Forum     Projects     Experiments     Circuits     Theory     BLOG     PIC Tutorials     Time for Science     RSS   

    Site design: Giorgos Lazaridis
    © Copyright 2008
    Please read the Terms of services and the Privacy policy