No IC Touch Sensor For.....whatever You Want!





Introduction: No IC Touch Sensor For.....whatever You Want!

This Design uses one wire that you touch and turns the load on or off. What is cool about this is you can actually use it as a proximity detector, it is sensitive enough to detect something from about a foot away. I did bread board tests and built one that detected me a turned a buzzer on from ten feet! The nice part about this design is that there aren't alot of parts and they are not expensive.

This is the same technology used in those ovens that have the glass panel over the controls, but they use ICs. The principal is the same however, they both detect (I think) the small electrical signals that people give off and amplifies this to a useful level. If this is wrong correct me, but all I know is that this works.

(This design works great for LEDs. I am making a touch LED flashlight that runs off rechargeable batteries, but I am not sure what batteries to get yet.)

Step 1: Parts

-4 x 2N3906 PNP transistors or similar (note below about transistors)
-1 x 1N914 diodes
-1 x 10v 1000uF capacitor (keep the voltage below 10v / Caps rated voltage or it will  
-1 x Barrel jack
-1 x 9v 300ma adapter
-1 x 120 Ohm resistor (Brown, red, brown)
-1 x Ceramic capacitor
-some shield wire (I don't use it because I don't have any but if you do use it!)
-some copper clad is nice to have but not needed
-ugly perf board
-Breadboard/protoboard are handy as well

-soldering iron
-tin snips for copper clad and ugly perf board

*Note: The transistors I used are random transistors similar to 2N3906 but I live in Canada and can only get a package of transistors "similar" to 2N3906 so protoboards are good to test this out on. Mine are bi polar and let some electricity through one way all the time wether they are off or turned around let no electricity through when off. Test the different combinations to get the way that works best. 2N3906 should work fine in this circuit though I have not tried it.

Step 2: Circuit

The schematic is shown below.

The only reason the resistor is needed is because the last transistor always began to over heat after about five mins. but with the resistor there it does not overheat anymore. You could try a similar transistor to the 2N3906 but with better power ratings and the resistor would not be needed, but as I said earlier, probably, I live in Canada and the Source by Circuit City doesn't have a good selection so I have no choice. So if you live in the States (USA) or buy parts online (thats what I should probably do) then test different transistors.

I would also like to add in an indicator LED to the board that way it turns on whatever the load is as well as a visual que that it is working.

UPDATE! - The transistors are all 2N4403 except for the one connected to the resistor. It is a 2N3906. Also I think the arrows in schematic might be on the wrong side or pointing the wrong direction, but they are PNP transistors. I did label the Collector, Base and Emitter in the picture in case I did the symbol wrong.

Step 3: Solder

The title of this step speaks for itself.

Also you can do a way better solder job then I can, probably.

Step 4: Done

Now was that not easy? A simple single wire touch sensor without complicated ICs for under $5 (mind you that that is the Canadian dollar!) ;)

one project that would be cool is to remove an on/off switch and replace it with a locking relay. You can buy small relays that are like pens, when they are switched on they snap closed and they lock and when they are switched again they unlock, then add in the touch sensor to control the coil of the relay.

Have fun and mess around with this design all you want. Also if anything is wrong in my Instructable, message me to fix it.



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    I'm pretty sure capacitive touch panels work on the principal that your skin is mildly conductive, while we do theoretically send out electricity from the neurons in your brain firing it'd require a ton of amplification to begin to detect, however the reason you get shocked so easily when you accidentally touch the outlet in your house is because your skin is significantly more conductive than air and thus the electricity can ground through you

    I didn't mean the small signals that our brain gives off, I meant the small charges that we build up that leads to a static shock. If you take a plastic rod, rub it, then touch it, you are mostly made of water and we ground fairly well so we gain some negative charge from the rod, and that is what this I think is detecting. I tried this while rub my feet on the carpet and it works better as you pull your feet across the carpet but in between each shuffling foot, you can see it dim a bit. Therefore, I don't think this would work if you were continually grounded.

    yes, it would still work if you were grounded, and it has nothing to do with the AC wiring. it's simply a matter of capacitance. being near the "touch plate" of the sensor changes its capacitance a very small amount. if it were caused by static, it would not sense you even a millimeter away from it, after touching it, because you would have just neutralized any difference of potential.

    This circuit works because you're in a house that has electric wiring. If you ran an extension cord out to the yard, it would become far less sensitive. The AC wiring in the walls gives off a small amount of electro-magnetic force (EMF) and your body acts like an antenna to pass it to the touch plate. Imagine a coil of wire connected to an electricit source; it gives off magnetism (specifically, electromagnetism). Uncoil the wire and it still gives off a magnetic field, it's just not as concentrated. This effect is similar to the noise you hear on an AM radio when your car drives under a high-voltage power line.

    ceramic capacitor of that value is?

    Hi there
    how can i wire this into the input of a PIC?
    pic 12f629 to be exact


    Connect the Output load to the PIC. Was that so hard?

    Honestly, I have no idea. I avoid IC's because I prefer building an entire circuit from scratch. That, and I self teach myself everything I know, and haven't gotten into IC's much...Sorry. :(

    @SMOKEDASPHALT-in DELHI !..that's damn cheap for us... for a touch sensor...!!!

    Here , in india,it can be build in under 2 $(canadian )