This circuit can be used for the safety of precious and valuable items. The low-cost electronic lock is suitable for use in homes and banks for lockers etc.The circuit consists of three thumbwheel switches, three DIP switch sets (each having eight switches), three inverter ICs (7404), three quad-AND gate ICs (7408), one quad-NAND IC (7400), one timer IC (555), few diodes/transistors and other passive components.
Circuit diagram :
Low Cost Electronic Clock Circuit Diagram
The Dip switches are supposed to be hidden and the actual code to be set on the thumbwheel switches must match the Dip switch settings, which will result in enabling of all AND gates (G1 to G11). The high output of the last AND gate is used for energising relay RL1 via DPDT switch S1, which in turn results in energisation of solenoid coil from mains supply via its N/O contacts. This causes the steel rod of the solenoid to be pulled against the spring tension and the lock gets opened. If the code selected via thumbwheel switches does not match the DIP switch settings and DPDT switch S1 is put on, the low output of AND gate G11 will result in setting of latch formed by NAND gates N13 and N14 as well as sounding of buzzer through transistor T2 which gets forward biased. Resetting of buzzer as well as the latch is possible by momentary depression of switch S2. It is therefore desirable to install switch S2 also in a hidden place.
For proper operation of the circuit, switch S1 is initially kept in off position and desired code is selected with the help of the dip switches. This is followed by resetting of latch by momentary depression of switch S2. Now the system is ready for operation. Switch S1 is to be put on only after correct code is selected with the help of thumbwheel switches for opening of lock (for energisation of solenoid), else it will result in sounding of alarm (buzzer), as explained earlier. Diode D2 prevents the positive voltage present at pin 1 of NAND gate N13 (when switch S1 is off) from reaching transistor T1 base and energising relay RL1 and the solenoid. A lock using solenoid coil can be easily fabricated even if it is not readily available. If required, the solenoid used in electrical gong type of bell may be used for the purpose.
Copyright : EFY
Post a Comment