Posts Tagged ‘Electronic lock switch’

Combination lock using PIC16F84

This is my electronic combination lock to use with an outdoor gate. The functionality is implemented in software. It turns on a relay (usually to open a door) for a few seconds if someone enters the valid code. Alternatively, it works as an ON/OFF switch, which toggles the relay each time the code is entered. This relay can operate a power-to-open type electric strike with a shorting contact or a power-to-hold type electromagnetic lock with a breaking contact (we need the relay because these locks usually work with AC, not DC). The code can be changed any time after entering the current code. Current consumption of the circuit is low, because the PIC sleeps most of the time, and wakes up only for processing key presses. If you don’t have a crystal, you can use the RC oscillator of the PIC16F84 as well, just check the PIC datasheets for details on oscillator configurations. The 16F628 already contains an internal RC oscillator, so no crystal is needed…
Read more source: http://jap.hu/electronic/combination_lock.html

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iButton DS1990A Lock

This electronic lock can be used with any type of iButtons you may already have, since the only thing needed is the internal serial number, that’s different for every iButton. The command used to read the serial number is the same for all iButtons. The iButton family code that goes with every iButton, can be anything and is calculated as part of the whole serial number. We must also notice that DS1990A series iButtons are the cheapest. This electronic lock designed to work stand-alone and it’s easy to construct. What the user sees (outside of the door for example) is a iButton socket and a led. ..
Source: http://www.electronics-lab.com/projects/sensors/001/index.html

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Simple Combination Lock by IC 4017 74C14

This simple combination lock accommodates codes from 1-9 digits long, with the only restriction being that the same digit cannot be used twice. The circuit shows strapping for a 4-digit code, in this case “2057″. Any unused switches are strapped to ground. When power is applied, the 330nF capacitor connected to pin 1 of inverter IC1a is discharged, holding it at a logic low level. The high output is inverted by a second gate (IC1b), with the result being a logic low on pin 4. This pulls Q1’s emitter low via D1, causing the transistor to conduct. The falling voltage on the collector then pulls the input of IC1c low, which in turn resets counter IC2.

On reset, output O0 (pin 3) of IC2 goes high, charging the 330nF capacitor via D2 and the 33k? resistor. If switch S2 is now pressed, Q2′s emitter will be pulled high and so Q2 conducts, applying a rising positive voltage to one end of the 1M? resistor. This resistor and the 33nF capacitor act as a switch “debounce” circuit, delaying the pulse through IC1e by about 33ms. After the delay, the output of IC1e goes low. However, counter IC2 does not increment at this stage, since it needs a positive-going edge at the clock input (pin 14). When the switch is released, Q2 turns off, IC1e’s output goes high after the debounce period and the counter advances to the next state (ie. O0 goes low and O1 goes high).
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Author: Len Cox – Copyright: Silicon Chip Electronics
Source: http://www.extremecircuits.net/

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