Electronic Code Lock
Published in issue 305, December 2001
Nowadays, electronic code locks are usually based on microcontrollers. However, if you like your electronics discrete, you will enjoy the battery-operated circuit shown here. Since the circuit automatically switches off after the door has been opened and draws no current in the idle state, three alkaline batteries (mignon, AA or R6 cells) are good for around 5,000 door openings. The main advantage is that the door opener can also be powered from the battery, so it’s not necessary to run any extra cables.
Resistors:
R1,R2 = not fitted
R3 = 220kOhm
R4,R5 = 1MOhm
R6 = 220kOhm
R7,R9,R10,R17 = 100kOhm
R8,R12,R14 = 2MOhm 2
R11 = 560Ohm
R13,R15,R20 = 1kOhm 5
R16 = 100kOhm
R18 = 120Ohm
R19 = 10k
R21-R24 = 3Ohm 3
R25-R35 = 22kOhm
Capacitors:
C1,C6,C7,C8,C10 = 100nF
C2,C3,C5 = 10nF
C4 = 1µ F
C9 = 330nF
C11 = 47µ F 16V radial
Semiconductors:
D1-D9,D11,D13,D14,D15,D17,D18 = 1N4148
D10,D12 = zener diode 1V2 0.4W*
D16 = 1N4001
D19 = LED, green
D20 = LED, yellow
T1 = BC327
T2,T3,T4 = BC337
T5 = BD140
IC1 = 4017
IC2,IC3 = 4069 or 40106
Miscellaneous:
JP1 = jumper
K1,K2 = 12-way pinheader or wire links
K3,K4 = not required (ribbon cable )
K5, K6 = 2-way PCB terminal block, lead pitch 5mm
S1-S12 = pushbutton with make contact
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Click below to download a PDF copy of this article from Elektor magazine. Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.
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