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Shorting a switch elctrically

  1. Dec 26, 2008 #1

    I have a switch, which is a normal push button switch. It does not latch. I need to design a simple electronics circuit that can be used to short the switch electronically. Any suggestion? I have tried using a transistor switching mechanism but it is not working properly. Any suggestion???

  2. jcsd
  3. Dec 27, 2008 #2
    You could use a relay and make what is called a seal in circuit. Energize the coil of the relay with the switch and use a normally open set of contacts from the relay to carry current around the switch. I am looking for a good diagram to post but maybe this will help for now.
  4. Dec 27, 2008 #3
    the problem with relay is that it consumes too much energy. I am trying to short about 4 switches in a digital circuit. which is abt 5 v. and most relays need nearly 9v.
  5. Dec 27, 2008 #4
    Here is an example of a seal in circuit.

    http://claymore.engineer.gvsu.edu/~jackh/books/integrated/html/integrated-140.gif [Broken]

    At the bottom is the switch, relay coil (M) and the contacts around the switch. The extra stop switch is used to allow the circuit to be turned off.
    Last edited by a moderator: May 3, 2017
  6. Dec 27, 2008 #5
    http://www.kelvin.com/Merchant2/merchant.mv?Screen=PROD&Product_Code=410006&Category_Code=ELPCRE [Broken]

    Here is a 5v relay.

    I know I have seen the same thing done in a digital circuit using transistors. I will look around a little.

    What types ICs do you have?
    Last edited by a moderator: May 3, 2017
  7. Dec 27, 2008 #6
    i am basically using a microcontorller atmega8 to give the switching commant to a RF module.. the RF module IC is some chinese IC which has nearly no datasheet on the net. It is using some ASK mechanism. thats why i resorted to shorting the switch instead of trying to hack the ic. The main problem that i got when i used Transistor switching is that for different currents the circuit responded differently. this circuit is seriously confusing. When i short it using simple wire it works fine but when i use some transistors for switching.. it acts crazy and even jams the entire RF range.
  8. Dec 27, 2008 #7
    Yeah, it would be good if you could drive it full on; like an scr. I don't know with what you have available. There are many examples of digital latch circuits but most are Flip-Flop based. There is this one made without ICs


    It seems like overkill to me but I don't have any more ideas at the moment.

    Someone on PF is bound to have some better advice. Good luck.
  9. Dec 27, 2008 #8
  10. Dec 27, 2008 #9
    thanks a lot.. will try it out and let u know..
  11. Dec 27, 2008 #10


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    Staff: Mentor

    You should measure the voltage on each side of the switch when it is open, and then again when the switch is closed. I may be pulling up to 5V instead of down to ground, which would change the topology of the simple transistor switch circuit.

    Worst case, you could use an Analog Switch IC to short out the pins. There's no reason to burn all the current of a relay for this application.
  12. Dec 27, 2008 #11

    It's impossible for me to tell what you're switch is switching. Ground, a digital signal, RF signal...?
    Last edited: Dec 27, 2008
  13. Dec 27, 2008 #12
    the time i needed something like this, i found a logic-level FET and it worked just swell.
  14. Dec 27, 2008 #13
    AN IC.. its a 5V digital signal
  15. Dec 27, 2008 #14
    Hmm. Well, that sounds like the comes-outa, but what's the goes-inta? That's really insufficient.

    If it fit, you might say something like: you want to switch a digital output to a digital input pulled high with 10K ohm, or so, and the both are 5 volt CMOS technology. Or maybe you want to multiplex signals, I don't know.

    You could require a transmission gate or simply an And gate.
    Last edited: Dec 27, 2008
  16. Dec 27, 2008 #15


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    Staff: Mentor

    I agree with Phrak and Proton Soup on this. When I said to measure the voltage on the switch pins in both open and closed states, I should have said to do it with an oscilloscope and not just a DVM. The results of the measurement might simplify Proton's suggestion, but if there is some analog or digital signal going across the closed switch, then you'll want to use a FET or analog switch IC.
  17. Dec 28, 2008 #16
    Currently i am at home and the circuit is with me, Since it is vacation i dont have access to the lab where the oscilloscope is. So as berkeman advices once the college reopens i will check it out. Thanks for the advice. the reason i am stuck with this shorting problem is because of some crap chinese chip IC SC2262. If i can get the datasheet for this IC which is in english and which is clear. I will be able to work even without Shorting as i can easily give commants from the microcontoller to the IC. If it is an AND or OR and logical operation that the switch must perform i can easily do with the micro cant i?
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