you want to make a code lock system in your home or office.
The circuit is actually a transistor switch; the switches from S1 to S5 are connected in series between the transistor base and the positive supply. The switches from S6 to S10 are connected in parallel across the base and the negative supply. The relay will only switch ON when all the switches from S1 to S5 and ON and from S6 to S10 are OFF. If any switch between S1 to S5 is OFF then the relay will not be activated and also if any switch between S6 to S10 is ON then the relay will still be in OFF condition.
After completing the circuit arrange the switches in a 0 to 9 number keypad manner. The operating voltage of the circuit is 5V to 12V DC. A power supply can also be used to operate the circuit. A relay switch should be of same voltage value as the supply voltage.
Here is a very simple and interesting project of simple one transistor code lock circuit. This circuit is using only few components, which are one transistor, two resistors, relay, diode and 10 switches. Although the circuit is based on few components but it performs very well and it is ideal if
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