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e-Key Secure Access System

Based on iButton™ ICs

e-Key Secure Access System
In this day and age it is trendy to put the letter e (for ‘electronic’) in front of many words, names and concepts, for example, e-business, e-life etc. We jump the bandwagon and describe e-Key, a controlled-access system based on iButton integrated circuits from Dallas Semiconductor.The circuit described in this article allows two relays to be controlled with the aid of electronic keys. These keys are based on components manufactured by Dallas Semiconductors, and go by the name ‘iButton’.Designed in the first place to switch alarm systems on and off, the ‘iButton’ component can have many other applications like controlled access to a PC, electronic door openers, etc.
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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 = 5k 6
R2,R4,R6,R8 = 10k
R3,R7,R9,R10 = 1k
R5 = 100k
Capacitors:
C1 = 100µF 25V radial
C2,C3,C7 = 100nF
C4 = 10µF 10V radial
C5,C6 = 22pF
Semiconductors:
D1 = 1N4001
D2,D4,D5 = LED
D3,D6,D7 = 1N4148
T1 = BC547
T2,T3 = BC557
IC1 = 7805
IC2 = AT90S1200 (programmed, order code 000089-41)
Miscellaneous:
K1 = 2-way PCB terminal block, raster 5mm)
X1 = 4MHz quartz crystal
RE1,RE2 = PCB mount relay, 6 V, 1 changeover contact, e.g., V23057-B0001-A101 (Siemens)
K3 = 9-way sub-D socket (female), PCB mount
K4,K5 = 3-way PCB terminal block, raster 7.5mm)
Keys = Serial Number iButton™ DS1990A (Dallas Semiconductor, RS Components, Farnell # 790-461)
Optional: key support DS9093A
Contact Reader for iButton™ DS9092 (RS Components, Farnell # 790-473)
PCB, order code 000089-1
Optional: project source code files on disk, order code 000089-11.
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