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FINGER TOUCH ACTIVATED SWITCH

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adrian22

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Hi,

Anyone has the circuit call FINGER TOUCH ACTIVATED SWITCH. Its like touch on a pad and it will activate, when u remove it will switch off. Anyone has the circuit which is simple for me.(maybe using resistor and transistor)

Regards
Adrian
 
There are mayn ways of doing this.

One is resistive this senses resistance between two plates.One is capacitive whith senses chages in capacitance in a plate.And one is radio wich senses a chage is the power pf radiovaves recived,this dose not work in a desert becose there are no radio stations there.
 
no easy

hi,

if you want to use only one plate it is not easy as you asked. you can search and get the idea from these circuits:


http://www.discovercircuits.com/C/capacitance-sw.htm#top

but if you use very close two plates, like the "Someone Electro" said this can be made more easily, not again one transistor of course! At least you need a circuit to drive the triac??

also there are ready ICs, like LS7232ND, you can find the datasheet and sample circuits. I am adding the pdf also.
 
The simplest way to do it is to use one of the QPROX chips. You can get them from digikey. Their single touch point chips are simple and from what I remember about $2.00.

The datasheets explain the setup and usually require a couple capacitors for setup, but that's it.

I have one here that I setup, but it was a year ago, and it never went anywhere passed just playing with it on a test board. Seemed pretty cool, but never found a practical use for it.
 
Maybe two plates is better, but i am just a newbie here so I am also weak in electronics. So is the circuit going if i use resistance. A finger has resistance so we can use resistance right? :roll:

Regards
Adrian
 
Yes, with twao plates you look for resistance change, and capacitance change in one plate. But you must protect the circuit to spikes and overvoltages.
 
The simplest way I can think of a touch switch is simply enclose in a fixture two plates that are nearly touching and cover the top plate with some rubber sheet that would be touched by the finger and apply the postive voltage to the bottom plate and the negative to the top plate. By depressing the rubber the plates will contact and the OP will be insulated by the rubber thus making a N/O contact into closed contact. This would work on any low voltage DC supply.

Cheers Bryan :D
 
Connect a pic output pin via a 4k7 or so resistor to an input pin.Connect the touch plate to the input pin. Change the state of the output, and in the next instruction determine the state of the input pin. If the plate is touched it will take longer to charge , and the state of the input will not change in the available time. Further code will take care of debounce, time delays,etc.
 
you need a sensitive amplifier.

Harry's homebrew pages has some amplifiers for you to build.

Just replace the input speaker with your finger. Your finger is now a resistor to the circuit.
 
you can turn a FET on by just touching a wire connected to its gate... it generally will stay on afterward for some time however, but with a sufficiently large resistor between the gate and ground you should be able to get it to turn off afterward but still respond to a finger.

and the best part is that you only need one plate, not two contacts.
 
spuffock said:
Connect a pic output pin via a 4k7 or so resistor to an input pin.Connect the touch plate to the input pin. Change the state of the output, and in the next instruction determine the state of the input pin. If the plate is touched it will take longer to charge , and the state of the input will not change in the available time. Further code will take care of debounce, time delays,etc.


Hi,

So how the circuit gose i am to blur with this project so sorry for the inconvi

Regards
Adrian
 
Doing it whith two plates it easy.You just need 2 transistors(and a reley if you want to swicth big loads.)
 
Someone Electro said:
Doing it whith two plates it easy.You just need 2 transistors(and a reley if you want to swicth big loads.)

Hi,

I just need switch a small load. So how it the circuilt going to be? What are the two transistors?

Regards
Adrian
 
There are two NPN transistors wired up as an dirgalitron.Giving it a huge gain.Then you have one plate coneted to the base and one to the positibe suply.So wen you toch bouth plates your figer will conduct a tiny curent from the 1st to 2nd plate.And that curent will thurn on the transistors wich thurns on the reley wich then thurns on the load.

Its so simple you cod design it your self.
 
Hi,

Is it connected like this ?

So what are the parts no. for the two transistor?

Regards
Adrian
 

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The transistor can be any small transistor.Just use what you have at hand.They can also be each difrent.
 
hi,

so what are the parts no. because i have not strudy about transistor yet so sorry i don't know anythings about transistors.

how is it connected then?

Regards
Adrian
 
Adrian, that's not a darlington configuration. A darlington is when the emitter of the first resistor is connected to the base of the second transistor.
 
then the 2nd transistor collector connect to the collector of the 1st transistor? but what the parts no.

Regards
Adrian
 
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