LED Touch Panel
Shine and touch
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.
Materials
Gerber file
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Component list
Resistors
(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
Capacitors
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)
Inductors
L1 = 10µH 760mA (Taiyo Yuden CBC3224T100MR)
Halfgeleiders:
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)
Miscellaneous
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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