How can I effectively short a push button switch using electronics?

[benzun_1999]

Hello,

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?

-benzun

 

[montoyas7940]

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.

 

[benzun_1999]

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.

 

[montoyas7940]

Here is an example of a seal in circuit.

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

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.

 

[montoyas7940]

http://www.kelvin.com/Merchant2/merchant.mv?Screen=PROD&Product_Code=410006&Category_Code=ELPCRE

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?

 

[benzun_1999]

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. that's 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.

 

[montoyas7940]

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

http://forum.allaboutcircuits.com/showthread.php?t=16694

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.

 

[montoyas7940]

OK, I said it and it didn't even occur to me!

You can make your own scr from two transistors. You need one pnp and one npn
connect them like this.

http://www.radio-electronics.com/info/data/semicond/thyristor/thyristor_equiv_circuit.gif

Switch the gate.

 

[benzun_1999]

thanks a lot.. will try it out and let u know..

 

[berkeman]

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.

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.

 

[Phrak]

Hello,

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?

-benzun

It's impossible for me to tell what you're switch is switching. Ground, a digital signal, RF signal...?

 

[Proton Soup]

the time i needed something like this, i found a logic-level FET and it worked just swell.

 

[benzun_1999]

It's impossible for me to tell what you're switch is switching. Ground, a digital signal, RF signal...?

AN IC.. its a 5V digital signal

 

[Phrak]

AN IC.. its a 5V digital signal

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.

 

[berkeman]

the time i needed something like this, i found a logic-level FET and it worked just swell.

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.

 

[benzun_1999]

Currently i am at home and the circuit is with me, Since it is vacation i don't 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 can't i?