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Touch-controlled Switch

With a PIC

Touch-controlled Switch
You don’t need special ICs when a capacitive (or ‘touch’) switch can also be realised with an inexpensive PIC controller. This article shows how it’s done.Over the past few years several manufacturers have come up with special integrated circuits for touch control switches. These ICs usually operate on the principle of capacitive change, work perfectly but are hard to obtain as well as relatively expensive. Fortunately, a capacitive switch may also be realised using ‘traditional’ means, i.e., a little physics and a microcontroller.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Resistors:
R1,R6 = 10kO (SMD shape 0805)
R2,R3,R4 = 100kO (SMD shape 0805)
R5 = 1kO (SMD shape 0805)
R7 = 470Ohm (SMD shape 0805)
Capacitors:
C1 = 470nF(SMD shape 1206)
C2 = 100nF (SMD shape 0805)
Semiconductors:
D1 = Chip LED, red, (SMD shape 0805)
T1 = BC847 (SOT23 case)
IC1 = PIC12C508A04/SO8, programmed, order code 030214-41
Miscellaneous:
K1 = 4-way mini PCB terminal block, lead pitch 2.5mm
PAD = sensor area (see text)
Disk, PIC source code file, order code 030214-11 or Free Download
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