Touch Sensor
Introduction
to DIY capacitive touch sensing
Edited by Lim Siong Boon, last dated 14-Jul-09.
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Topic Discussion Overview
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1. Touch sensor IC and products
Various capacitive touch sensor products
Quantum Research Group Capacitive touch sensor QT100, QT102, QT110, QT113, QT118H, QT220, QT240, QT1081, QT1103, QT60160, QT60168, QT60240, QT60248, QT60326, QT60486, QT411, QT511, QT1106
Capacitive touch sensor: QST108, QST1610, STMPE1208S Resistive touch sensor: STMPE811
Capacitive touch sensor: B6TS-04LT, B6TS-08NF, B6TS-16LT
Sensor Platforms Capacitive touch sensor: SSP1401, SSP1492
Analog Devices Capacitive touch sensor: AD7142, AD7143, AD7147, AD7150, AD7151, AD7745, AD7746, AD7747 |
The following circuit DIY touch
sensor will be focusing oncapacitive sensing method. In case you think that
capacitive is the only method to implement touch sensing, I have done some
searching and list down the possible method and technology to achieve
similar touch effect as the capacitive method. Just a short brief of the
various touch sensing technology available in the market for your reference. The various types of touch sensor. - Capacitive - Resistive "4 wire/ 5 wire/ 8 wire" - S.A.W "surface acoustic wave", Acoustic - InfraRed - Camera
Capacitive type are normally used in a simpler button switch interface, which are commonly available on portable gadgets like mouse, ipod, and the On/Off switch for your LCD monitor. This method senses the changed of capacitance when the user come in close contact on the switch plate surface. Capacitive touch sensor can be implemented using microcontroller with simple interfacing component. You may like to refer to Microchip or Texas Instruments website for implementing touch sensing using a microcontroller, mTouch.
PDF Article: Layout and Physical Design Guidelines for Capacitive Sensing PDF Article: Software Handling for Capacitive Sensing PDF Article: Capacitive Multibutton Configurations
PDF Article: PCB-Based Capacitive Touch Sensing With MSP430
Fortunately there are already integrated hardware solution in the form of IC chip, making it easier to integrate touch sensing into your gadget. On the left are some references for the various source of IC chip.
The following are some of the touch solution available.
SAW acoustic sensor
Cherry IR touch panel A simple IR emitter and detector for touch sensing.
Another method of detection using IR sensor, by sensing the lights that is being blocked (the IR component looks like a LED). http://web.ndak.net/jdgrotte/touchsensor/touchsensor.htm
IR sensor deployed in grid form,
creating a IR sensing touch screen.
Touch technology base on camera.
- IR camera.
more: http://www.instructables.com/id/How-to-Make-a-Cheap-Multitouch-Pad/1
- Whiteboard using the Wiimote.
http://uiui.mmdays.com/2008/03/29/johnny-lee/
- LED Multi-touch panel (click the picture for reference)
Comparison references for various touch sensing technology. PDF Article: Touch Screen Technology Comparison http://www.tvielectronics.com/Touch_Screen.html http://www.softtouch.co.in/compareTouch.htm
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| 2. Touch sensor circuit | |
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Simplest touch sensor circuit The illustration on the left shows a simple touch sensor circuit. It will light up the LED when a person gets in contact with the wire or metal connection to the transistor base. This touch circuit is cheap and easy to construct. All you need is a npn transistor, a resistor, a LED, a metal contact surface and of course the wire connection. It is so simple. NOTE: Interface the circuit will requires a bit further improvement to the design. Do not connect the ground reference to the earth. The LED will either not light up or will be very dim.
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Capacitive touch sensor circuit using QT100
Touch sensor schematic. (click for larger image)
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Using QT100
QT100 IC pin out |
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Various others touch circuit that I have found on other website:
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Testing out with my first touch
sensor prototype board. It is actually more sensitive than expected. The
sensor board can sense my finger at a distance of about 10mm. The
circuit is quite simple to setup with only a few passive resistor and
capacitor components. I am suppose to make the board a plate for sensing the capacitance, but I only wired the sensing plate in a form of L shape path. It is working well just like a rectangular sensing zone, even though the plate is actually a thin L shape path. One thing I found out. It is too sensitive. the sensor also detects if I place the board near my wooden table platform. You can actually fine tune the sensitivity by using a different capacitance component. Try reading the datasheet for further information on using QT100 touch sensor. You can find more tips on making your own touch sensing device. The following videos demonstrate the signal out put you can expect from QT100 touch sensor IC. Touch sensor is sensitive |
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Keyword: Touch sensor switch, proximity, capacitance, capacitive touch sensing, surface acoustic wave, resistive 4 wire 5 wire
Resistive touch sensor is commonly deployed in our touch
panel
LCD monitor.
Acroustic sound sensing,
by sensitive object.
