You only need 3 components.
A transistor, a resistor and an LED.
See the video below to see how I connected it. Or skip the video if you prefer to read how to connect it.
Connect the resistor and LED in series from the positive supply to the collector of the transistor. Choose a resistor that sets the current of your LED to around 20 mA.
Connect the emitter of the transistor to the negative terminal of the supply.
Now, create two wires with exposed ends – so you can see the metal.
One goes to the positive supply. The other goes to the base of the transistor.
This is all it takes.
Now, try to touch these two wires with your finger – and the LED lights up!
The reason is that your finger acts as a resistor and will give enough current to the base of the transistor to turn it on.
This is one of the circuits you will build in «Getting Started With Electronics». Along with other fun and simple circuits, to get you started in electronics. Get it here:
https://www.build-electronic-circuits.com/products/getting-started-with-electronics-ebook/
Keep on Soldering!
Oyvind
StarDust says
That’s more clearly even I know how to build it.
victor says
Pls explained the it wel ..I have never use vero board before so create a video on how to link components on vero board …pls that just i need for now…thanks
admin says
Veroboard is the same as a stripboard – check out this: http://www.build-electronic-circuits.com/stripboard/
Cheers!
Oyvind
jsrobson10 says
It’s nearly the same as a stripboard, just a little different.
https://goo.gl/images/ALQmeh
This image shows the breadboard and the black lines show where it conducts the electricity.
calvin says
good i wanna try it
joyce says
If i touch a wire with my right hand and the other with my left does the LED turns on?
admin says
Exactly =)
TR pooja says
I tried it in a breadboard but it doesn’t work .
Can u pls explain.
admin says
Hi,
It could have something to do with the LED and the resistor you use. Try a lower resistor value for R1, such as 100 Ohm.
Best Regards,
Oyvind
Hari says
Sir, please explain the application &use
N V S Akhil says
hello plz could u help me to build a simple touch circuit
Vishy the Fishy says
hey buddy ty for the idea
Rohan Indurkar says
Sir I need your help I want your email ID please mail it to me
Faseeh Haider says
SIR PLEASE GIVE ME ITS PLACEMENT ON PCB ,, I NEED IT BADLY
simo says
Hi thank you for your post. I would like to make a variation of your circuit to apply it to a problem I am currently working on: I want circuit A to send a signal when I switch it on by touching with my left hand, and circuit B when I touch it with my right hand. Now, those circuits have a common ground and in order to close circuit A for example I have to touch the common ground and the other branch of the circuit with my left hand. However when I tested it I detect a cross talk that I am not sure how to get rid of. Do you have any suggestions on how to make it work?
Axel says
Thanks for this fun little project. Took me a while to find a transistor that could do the job, but in the end I used an old BC237 that I had laying around.
The circuit is fun as I can see the led intensity change based on the wetness of my finger, ie how the base current controls the collector to emittor current.
samantha says
In your other transistor tutorial you use a battery to supply current to the base to turn the led on and off which makes sense to me. However I am still confused about how your finger is supplying the current. Is it because you are completing a seperate path for the electrons to flow from negative to positive? Thank you!
admin says
The current flows through my finger from plus to minus. Without the finger, there’s no path for the current to flow through the base. The finger acts as a resistor, allowing some current to flow from plus, through the finger, through the base and down to minus/gnd.