Wiring & diagram Info

A very simple electronic key code lock circuit that require few external components can be constructed using this schematic diagram . This electronic key code lock circuit is based on a common 555 timer circuit and some other common components .

This low cost key code circuit use six switches that needs to be pressed to open the lock, but only two switches at a time. In many other , more expensive electronic circuits the key code is formed by pressing some switches one by one , not like in this case two switches . If you don’t like to press two switches in the same time you can eliminate one switch , but in that case the code can be more easy to guess by someone ells .Thus a total of three sets of switches have to be pressed in a particular sequence. (Of these three sets, one set is repeated.)

An essential property of this electronic code lock is that it works in monostable mode, i.e. once triggered, the output becomes high and remains so for a period of time, governed by the timing components, before returning to the quiescent low state.Pin 2 of 555 timer is the triggering input pin which, when held below 1/3 of the supply voltage, drives the output to high state. The threshold pin 6, when held higher than 2/3 of the supply voltage, drives the output to low state. By applying a low-going pulse to the reset pin 4, the output at pin 3 can be brought to the quiescent low level. Thus the reset pin 4 should be held high for normal operation of the IC.

Three sets of switches SA-SC, S1- S8 and S3-S4 are pressed, in that order, to open the lock. On pressing the switches SA and SC simultaneously, capacitor C3 charges through the potential
divider comprising resistors R3 and R4, and on releasing these two switches, capacitor C3 starts discharging through resistor R4. Capacitor C3 and resistor R4 are so selected that it takes about five seconds to fully discharge C3.

Depressing switches S1 and S8 in same time, within five seconds of releasing the switches SA and SC, pulls pin 2 to ground and IC 555 is triggered. The capacitor C1 starts charging through resistor R1. As a result, the output (pin 3) goes high for five seconds.Within these five seconds, switches SA and SC are to be pressed momentarily once again, followed by the depression of last code-switch pair S3-S4.

These switches connect the relay to output pin 3 and the relay is energised.
The contacts of the relay close and the solenoid pulls in the latch (forming part of a lock) and the lock opens. The remaining switches are connected between reset pin 4 and ground. If any one of these switches is pressed, the IC is reset and the output goes to its quiescent low state.

The below Simple Timer with Transistor Circuit Diagram is a simple timer that uses only two Darlington transistors and a capacitor base to generate a delay. When SW1 is pressed, the timer starts, the time setting is set by VR1. The duration of the timer is given by the values ​​of the potentiometer VR1 and the capacitor C1 that this schema is 220 pF. To reach other durations of time must change the values ​​of these two components.

This electronic schema is a very nice and simple alarm schema that is based on the 555 timer integrated schema. This alarm schema can be used with many types of sensors like : light or temperature sensors. As you can see below some types of sensors that can be connected at this type of alarm schema ( darkness , light , cold and heat sensor ).

If the sensor detects that the temperature or light is outside of the desired range the alarm will be activated .By turning the  potentiometer from the base of Q1  you will modify the sensibility of the sensor . When the alarm is activated the Q2 transistor acts as an audio amplifier and speaker driver for the 16 ohms speaker .

Dual Sensor 555 Timer Alarm Circuit Diagram

This alarm schema require a 12 volts DC power supply schema .