DIY Touch Sensor

by giladlotan

193K27678

Intro: DIY Touch Sensor

This is a short instructable on how to use the Qprox IC (QT113G) as a touch sensor. Using this IC, you can essentially turn any object into a touch switch. This simple circuit may be hooked up to a microcontroller (in this case I used the MAKE controller board).

STEP 1: Gather All the Necessary Parts

1. QT113 - can be ordered at Digikey DigikeyDigikey. Each one costs around $2.
2. 10mF capacitor
3. Wires
4. LED
5. breadboard or perfboard (if you choose to perf, you will obviously need a soldering iron and some solder)

STEP 2: Build Your Circuit

wire up your circuit according to the following diagram:

pin 1: Power (3.3-5V)
pin 2: Output (in this case I used a red LED)
pin 3: Ground
pin 4: Power
pin 5: Power
pin 6-7: 10 micro Farad capacitor. These pins also connect to the input wire.
pin 8: Ground

STEP 3: Input Wire

Strip the tip of the wire and embed it into or behind an object or the surface which you want to act as a touch switch. when connected to a conductive metal sheet, or mesh this works really well. When doing multiple switches, it is important to make sure the surfaces are surrounded by ground, so as to protect each distinct touch surface.

You can see how the light turns on and off when my finger touches the wire.

STEP 4: Connect to a Microcontroller

In this case I used the MAKE controller - connected the output wire from Step 2 (which was an LED there) into the 4th Input pin of the controller board. When touched, the pin goes low, otherwise its state is high.
In this example, I used the NET connect software to create a flash animation that changes its shape according to a user's touch.

Good Luck!

77 Comments

Mark Collins 8 years ago

https://www.instructables.com/id/TouchWire/ This is way more better than this cuz it does not require any hardware except an wire and an arduino...

didgitalpunk 8 years ago

no, because you can't make your arduino the size of your thumb nail, not only that,
but using a pin on your arduino and some of it's memory for such a simple task isn't worth it. also, your arduino is hardware, and it's way more expensive than this little chip, or any field effect transistor and some caps/resistors.

splud 6 years ago

I can understand your perspective with respect to a full-on Arduino board perhaps, there are a variety of bare AVR microcontroller ics that are actually MUCH less expensive than the original IC used for this project (when it was still available). To top it off, many of those natively support capacitive touch. I use ATTiny13A uCs in a number of projects, and those can be sourced for less than US$0.50 apiece in single unit quantities, and can drive your logic. ATTiny85 uCs are documented to support 3 QTouch channels:

http://www.microchip.com/wwwproducts/en/ATTINY85

The ATTiny13A is listed as one of many supported devices on a QTouch informational page, although its own datasheet makes no mention for such support. I don't personally use it for capacitive touch, so I can't say one way or another for QTouch library support, but it would certainly support a more direct approach to capacitive sensing.

The package size for the 8 pin ATTiny devices solidly qualifies as smaller than your thumbnail. They're commonly programmable using the Arduino IDE.

Note that capacitive touch can be used for more than simple on/off buttons - sliders and dials can be implemented using it - mostly via a carefully constructed PCB pattern.

While I haven't tried to make this particular project (esp since the IC is NLA), one can readily find ICs with similar functionality, such as the AT42QT1012-MAHR (there are a host of devices in the ATxxQTxxxx line - AT for Atmel and QT for QTouch. which is capacitive sensing), which is about 1/5 of the price mentioned for the original IC employed here.

Mark Collins 6 years ago

Ah, this comment is pretty ancient.. It was from a period where I just started learning electronics. Now my knowledge on the matter is quite a lot compared to that time. I would recommend using something like the MPR121 if you needed alot of inputs and have a separate micro-controller IC. Although if a low amount of inputs are required I would go with something like the ATTiny85 just as you suggested (Also I thank you for introducing me to QTouch although I have moved on to the ESP8266 and RPi Zero W development after that point)..

jblackwood 7 years ago

I wonder if this can be used for paddle shifters? I want to use a pair of titanium D shaped rings rigidly mounted behind the steering wheel and use capacitive sensing to switch whenever a hand (or a gloved hand) approaches the D ring. I tried the NXP demo board, wiring it to the D rings instead of the small pads on the board but it was too sensitive and I got a lot of crossover interference between the two circuits. Tried a Turk flat prox under the mounting plate hoping that transferred capacitance might work but all that did was switch the prox on. Anybody got any ideas how a simple arrangement might work? I have a 5v supply and need logic level inputs going high on activation. The simpler the better as long as it works reliably.

Jim

Abhi909 8 years ago

great project

can i place your project on my website.

i'm working on a website which is related to electrical projects.

i also mention your name, link and other info.

plz reply

salto 8 years ago

You can check AT42QT1010 (1 channel) chip for project like this.

JetMechanic 8 years ago

QT110, QT113 not widely available in North America as of November 2015.

awesomevicky 9 years ago

What is the use of micro controller?where i can get it?and how to use it in this project? Please help

awesomevicky 9 years ago

What is the use of micro controller?where i can get it?and how to use it in this project? Please help

awesomevicky 9 years ago

What is the use of micro controller?where i can get it?and how to use it in this project? Please help

awesomevicky 9 years ago

What is the use of micro controller?where i can get it?and how to use it in this project? Please help

leo_oto 12 years ago

Hi All,

I'd great results with AT42QT1011 ( 6 cm of detection) but i have some issues.
Is it possible to connect the chip to the sensing plate with 1 metre cable and avoid interference?
Which method should i use (gnd shield, driven shield)?

slopes 13 years ago

Is this the same Touch switch IC as sold here?

http://www.hobbytronics.co.uk/manufacturer-hobbytronics/touch-switch-ic

lasermaster3531 12 years ago

no, that one is actually a little bit better. It has two inputs, so you can control two devices with one IC.

teche 12 years ago

if you put a relay where the led is placed you can put 240v put 240volts through it and use it to turn off your lights at home :)

lasermaster3531 12 years ago

only problem is that the ICs can only handle 2mA at 5 volts. that isn't enough to power the most anorexic relay, so you will need it to drive a feild-effect transistor (FET) to drive the relay. not too complicated but make sure the FET is there otherwise you may burn the IC out.

kthunt 12 years ago

I was looking at Digikey (which seems like about the only source for this line) and Atmel. It looks like they have mostly discontinued this chip set and replaced it with the QT1010-12.

The QT1010 and QT1011 work like the QT113 in basic mode. Only on while touched. The difference is the 1010 has a stuck key timer. These are good for keyboard, switch use.
The QT1012 only operates as an on/off toggle, like for lamps and such.

Also, the default output level has been changed to active-high so you don't have to invert the signal any more.
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