About the article

Code Lock with One Button


Code Lock with One Button
The unusual feature of this code lock is that it can be operated with just one pushbutton. In situations where a tamper-proof solution is required this circuit has a great financial advantage: only one robust pushbutton needs to be bought. The disadvantage of this solution is that it takes a little longer to enter the code.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD 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.

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Extra info, Update
The circuit diagram should be modified to show a common-cathode (CC) display in position LD1. A suggested type is the LITE-ON LSHD-5503. Supply decoupling capacitor C1 is not shown on the component overlay and may be fitted at the underside of the board.
R1-R8, R11 = 1k
R9 = 100
R10 = 6k8
C1 = 100nF
D1 = LED, green, low-current
D2 = 1N4148
IC1 = PIC16F84 (programmed, order code 040481-41*)
LD1 = 7-segment display, red, common-anode (e.g., Kingbright Sc56-11SRWA)
T1 = BC547B
JP1 = 3-way SIL pinheader with jumper
K1 = 3-way PCB terminal block, lead pitch 5mm
Re1 = relay, 5V coil, (e.g., Omron G6A-234P-ST-US-DC5)
S1 = switch, 1 make contact, tamper proof (see text)
X1 = 4MHz ceramic resonator
PCB, ref. 040481-1
source and hex code, ref. 040481-11
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