S3193586 The art of capacitive touch sensor - PROJECT 4
From Physical Programming
Contents |
How the device operates
Touch sensor is a common type of sensor that had appeared for many years. It is practical and valuable enough to replace the mechanical switches because of the recent advances in mixed signal programmable devices.
The standard touch sensor’s cap is designed meant to be 3mm or less. It’s getting harder to sense the finger because the thickness of the cap is getting ticker. However, the process of tuning is getting easier. This is because the cap made out of glass so the user can see the underlying sensor pads clearly. It also has direct application in called ‘white goods’ (household appliances.)
In the middle part of the touch senor, there’s a set of conductors that interact with electric fields. What makes the touch sensor works is because of the human body. Conductive electrolytes can be found in the tissue of the human body, which covered, by a layer of skin.
To make a practical touch sensor, you have to design a set of printed circuit traces, which can direct the fringing fields into the active sensing area.
What’s fringing field?
Fringing field is the energy that spills outside the sensing area when you having a simple parallel plate sensor, which has two conductors, separated by a dielectric layer. Mostly the energy will direct between the plates.
If you place your finger near to the fringing fields, the conductive surface area will added to the touch system. Finger capacitance, CF, is the additional charge capacity from the finger. And for the CP, which is parasitic capacitance means the capacitance of the sensor without a finger present.
There’s a common misunderstanding about touch sensor is finger has to be the one to make it work. This is because a finger can hold the charge when the finger is floating or grounded.
What the device is typically used for
Touch sensor are widely used nowadays. You can found touch sensor appear in different categories such as
- Proximity sensing (personnel detection, light switching, vehicle detection)
- Measurement (flow, liquid, pressure level, thickness measurement)
- Switches (lamp dimmer, key switch, limit switch)
- Communications (wireless datacom, cell phones)
- Computer graphic input (x-y tablet)
liquid level
vehicle detection
wireless datacom
How it can be interfaced with the Arduino micro-controller
Using a touch sensor as a switch to turn on the light.
Step 1:Prepare the material
1) QT113
2) 10mF capacitor
3) Wires
4) LED
5) Breadboard
Step 2: Build the circuit
Set up the circuit according to the diagram below
pin 1: Power (3.3-5V)
pin 2: Output ( choose any colour you like)
pin 3: Ground
pin 4: Power
pin 5: Power
pin 6-7: 10 micro Farad capacitor. These pins connect to the input wire.
pin 8: Ground
Step 3:Input the wire
Make the tip of the wire and enter it into an object or the surface you proffered to act as a touch switch. This will the whole touch sensor works really well when connected to a conductive metal sheet. It is important to make sure the surfaces are surrounded by ground to protect different touch surface.
http://www.instructables.com/id/DIY-Touch-Sensor/step3/Input-wire/
Examples of interactive projects using this sensor technology
1) Tau' remote control
http://www.fierceiptv.com/story/ruwido-adds-capacitive-sensor-tau-remote-control/2010-07-12
2) Hidden input elements.
http://interactive-matter.org/2009/07/arduino-ad7746/
3) A Compact, Wireless, Wearable Sensor Network for Interactive Dance Ensembles
http://www.computer.org/portal/web/csdl/doi/10.1109/BSN.2006.1
References
http://www.instructables.com/id/DIY-Touch-Sensor/#step1 (for the question 'how to interfaced')
http://itp.nyu.edu/phsycomp/sensors/Reports/SoftPot
http://www.analog.com/library/analogDialogue/archives/40-10/cap_sensors.html
