About the article

LED Touch Panel

Shine and touch

LED Touch Panel

A touch panel can be made in several different ways. Although the method described here has been known about for a substantial number of years, it is rarely used in practice. Despite this, it is very interesting and it’s certainly worth experimenting with. The theory: Two IR LEDs transmit light. When a finger is above them the light will be reflected off it, which can then be detected by a third IR LED that has been configured as a detector at that point in time.

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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.

Controller Board
(all SMD 0805)
R1 = 300kOhm
R2,R9,R23,R33 = 1.5kOhm
R3–R7,R10,R11 = 2.2kOhm
R8,R18 = 10kOhm
R12 = 330Ohm
R13–R17,R19,R20,R21,R24,R25,R26,R28–R32 =33Ohm
R22 = 1kOhm
R27 = 4.7kOhm
R34,R35 = 27Ohm
C1 = 22µF 6.3V tantalum (Kemet shape C)
C2,C5,C6,C8,C10,C12,C13,C14,C16,C17,C20,C21,C23 = 100nF (SMD 0805)
C3,C27 = 33µF 16V tantalum (Kemet shape D)
C4,C7,C25 = 1nF (SMD 0805)
C9 = 1µF 16V (XR7 SMD 0805)
C11,C15 = 4.7µF 10V tantalum (Kemet shape A)
C18,C19 = 10pF (SMD 0805)
C22 = 33pF (SMD 0805)
C26 = 10nF (SMD 0805)
C24,C28 = 15pF (SMD 0805)
L1 = 10µH 760mA (Taiyo Yuden CBC3224T100MR)
D1 = 3.3V 0.25W zener diode (SOT23)
D2 = LED, red, 25mA (SMD 1206)
T1 = BC857C (SOT23)
IC1 = LM1117MP-3.3 (SOT223)
IC2 = OPA2340UA (SO8)
IC3 = AT91SAM7S256-AU-001, programmed
IC4 = HCF4067 (SO24)
IC5,IC6 = A2982SLW-T (SOIC20)
IC7 = ULN2803AFWG (SOIC18)
X1 = 18.432000MHz quartz crystal, HC49/4H_SMX
S1,S2 = SMD pushbutton, 6.5x6.5mm (e.g. Panasonic EVQQQ2503W)
K1,K2,K3,K5,K6 = 8-way pinheader receptacle, lead pitch 2.54mm
K4 = Mini-USB-B chassis socket SMD (e.g. Molex 675031020)
PCB # 070588-1

LED Board
D1–D64 = IR LED, 5 mm (e.g. Vishay TSUS5202)
K1–K4,K6 = 8-pin pinheader, lead pitch 2.54mm
PCB # 070588-2
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