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Touch-2-Switch

Versatile capacitive switch in a wall box

Touch-2-Switch
This capacitive-detection dual wall touch-switch, designed to fit into domestic electric wall-boxes, uses analog technology throughout. A single multi-purpose version that you can configure as you wish to function as a simple on/off switch, a 2-way switch, or momentary button, on two independent channels. At low cost, modernizing your home electrics has never been so tempting.
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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.

Component List
Resistors (SMD 1206, 5%)
R1,R2 = 47Ohm 0.25W
R3,R9,R11,R12,R29,R30 = 470kOhm
R4,R19,R24 = 120kOhm
R5 = 330kOhm
R6,R7 = 2.2MOhm
R10,R13,R27,R28 = 10kOhm
R20,R22,R23,R25,R26,R31,R32,R33 = 1kOhm
Capacitors (ceramic, SMD1206, 20%) 
C2,C3 = 4.7µF 16V
C4 = 22pF 50V
C7,C8,C10,C12,C16,C17,C18 = 100nF 50V
C9,C13 = 4.7nF 50V X7R
C11,C15 = 1nF 50V
Capacitors (miscellaneous)
C1 = 470µF 25V, Panasonic EEEFK1E471AP, (1244419)
C5 = 100nF 305V, X2 Class, 15mm pitch, Epcos B32922C3104M (1112840)
C6,C14 = 100µF 25V, Panasonic EEEFK1E101AP (1244416)
Inductors
L1 = 22µH 0.11A, Multicomp MCFT000190 (1711917)
Diodes
D1,D5,D6 = BAT54 (9526480)
D2 = BZX84C12 (1902445)
D7,D8,D9 = LED, yellow, Kingbright KPT-3216SYCK (2099249)
Semiconductors
Q1,Q2,Q5,Q7 = 2N7002ET1G (2317616)
U1 = TPS62120DCNT (1864820)
U2,U3 = AT42QT1010-TSHR (1841593)
U4 = SN74HC74D (9591680)
U5,U6 = ZXGD3005E6TA (1904033)
Miscellaneous
F1-1 = fuse holder, Littelfuse 64900001039 (1271673)
F1-2 = fuse, 5A slow, 5x20mm, Schurter 0034.3124 (1360818)
J1 = 2-way PCB spring terminal block, 5.0mm pitch, Wurth 691414720002 (1841365)
J2 = 4-way PCB spring terminal block, 5.0mm pitch, Wurth 691414720004 (1841367)
J3-1,J4-1,J5-1,J6-1 = 10-pin pinheader, low profile, 0.1” pitch (1668506)
J3-2,J4-2,J5-2,J6-2 = 10-way receptacle, low profile, 0.1” pitch (1668102)
K1,K2 = relay, bistable, 12V, TE PE014F12 (9913459)
R8 = varistor, 300V, Epcos B72205S0271K101 (1004358)
GL1,GL2,GL3 = LED light pipe, Bivar PLP2-375, (2293497)
PCBs 130272-1, 130272-2, 130272-3 (elektorPCBservice)
(numbers in round brackets are Farnell/Newark order codes)
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