# Key code lock switch circuit

This key code switch circuit is a type of electronic circuit that is created to replace conventional normal key switch. Without inserts a keys.
But you can press the number code instead of unlock keys. We do not have to carry a load key and do not worry about your keys are lost. We just must remember to commit to a code only.
Feature of this circuit
– For in this circuit uses a four numeric code number and this code number can be changed up to one thousand numbers.
– The case with other people to know our original code. They code can be changed easily.

The circuit is designed to have the reset system, immediately enter the wrong code. so can prevent pressing a random numeric code. Because in this circuit the switches are set to the ten numbers, be the code switch 4 pcs. and be reset switches 6 pcs.
The advantages of having a system reset, suppose we set the code number is 6583, If people do not know the code, they will press random from 0 to 9, It will be has one correct number is 6. But the press randomly in the second round. Not that he would press any number that not the 5, The circuit will reset a number 6 which was originally to be released.

So he will enter a code be correctly, just the first digit only. However, if as without the reset system. Even those who do not know the code, it can be opened is the random pressing in a fourth round only.

When he hit 0-9 from the first round he will correctly hit to the No.6. then he hit the second round will correctly is one no.5 as well. When the full four rounds, it would has a four code so the circuit is working. This difference is quite obvious. When talking about the advantages – and disadvantages, then to look at the circuit and how it works really well.

How it works

This circuit uses an 74HC4017 or CD4017 IC Number that is DECODE Counter model. It serves to change the code. In normal conditions, when we provide a power supply to this circuit be has a positive voltage output at pin 3 of IC1. When you press the switch A-S1, The positive voltage from pin 3 to pass switch to the pin 14 of IC1, which is an input pin.
Then when IC1 has the input is positive voltage, it will move the output from pin 3 to pin 2. so the next switch that must to press to be the switch B – S2 for has the positive voltage at the input of IC1 in next step. As you can see, if we do not press the switch B, it will not change any of the IC.
And if we push a switch wrong away, to press switch that be one of six options on the left hand side of this circuit. It is the positive voltage pass the switch to the input pin 15 that be reset of IC1, When does it matter the pin 15 is given the positive voltage, IC1 will change the output to at pin 3, so it is resetting switch A to restart new again.
If you press the correct always from ABC to D, IC will move output to Pin 10. Which is pin be connected through a diode, and R-10K to pin B of the Q1-2N3904, making the Q1 is conduct, Ry1-relays and LED’s are working together to relay, the light to this circuit work, then let us know. For the five diode that connected to the out of IC1 You are prevented Output is provided to prevent is disturbanced in the code that the two codes are the same as 5385 code.

The connection of keys code.
When we need any code, I provide a call from that number to switch positions, switch A is the first number you want. and The two codes are linked to the switch B, The third code to link to switch c, The four code to link to switch D, All switch the remaining 6 digits or S5 to S10, connect it all together at the N.

The parts of circuit
IC1___________74HC4017 or CD4017 ___DECODE Counter model
Q1____________2SC458 or 2SC1815 or 2N3904 ____45V 100mA NPN Transistor
RY1___________Relay 9V____one contact 5A
C1____________100uF 25V____ Electrolytic Capacitors
R1,R2__________100K_____ 1/4W Resistor
R3_____________10K______ 1/4W Resistor
R4_____________1K______ 1/4W Resistor
LED1___________LED any color 3mm.
S1-S10__________Switch Tactile ON OFF Single Pole, Single Throw Round Button

How to builds this project.
If you would to build this project can assemble them on universal PCB because fast and saving.
But you need to make the general PCB, please see on Figure 2 and all components layout. so easy to builds.
Note: Q1 you can use a lot of number that is NPN transistors but the position legs is different.

Figure 2 the PCB and All components layout of this project.

The creation and applications
You should to include a variety of devices to correctly the schematic. Should equipment installation is small before such as R, Diode, IC Socket, etc. followed by a large device. When installing the equipment Already, Check to see everything properly before inserting the IC1 into the IC Socket. Then to connects the power supply to this circuit, and to test with pressing code set, if the relays work will be as compatible.