Electronic Master combination lock: Construction Explained

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In the previous article we have learnt the construction details of the electronic master combination lock circuit. Here we will deal with the remaining and the final part of the article regarding the functioning and the testing procedure.

Functioning And Testing

You can refer one of previous article on ‘the pin designation of IC 4017’ to get a better view of the present circuit. Their we have seen that when a clock signal is applied to pin 14 of the IC 4017, its out put sequentially change state, i.e. a logic hi out put is shifted sequentially from a starting point( pin 3 ) to an end point( pin 11), where it is reset back to the starting point and the cycle repeats. The process takes place serially in the following order of its pins : 3,2,4,7,10,1,5,6,9,11.

The readers should know that a clock signal is nothing but an alternate creation of a logic hi and a logic lo. This can also be manually generated by toggling a positive signal through a push-to-ON switch.

Getting back to the circuit of the electronic combination lock, the functioning can be explained as follows:

  • Assume that the code number of the electronic combination lock is set as ‘4 7 1 0 2’.
  • Initially as soon as the supply is switched ON , capacitor at pin 16 charges and resets pin 15 of the IC ( power-ON reset ), so that a stable logic hi appears at the starting pin 3 of the IC.
  • As per the diagram of the electronic combination lock, the first code (no.4) is connected to this pin, so obviously on pressing this key (code 4) a logic hi is sent to the base of the transistor connected to pin 14 of the IC.
  • It instantly conducts and pulls pin 14 of the IC to ground. On releasing the key the transistor stops conducting. This means, at this instant a logic hi is restored back at pin 14 through resistor 1 M.
  • The IC takes this as a clock pulse and the logic hi from pin 3 is shifted to pin 2 of the IC.
  • Again we will find that the next code (no.7) of the electronic combination lock is connected to pin 2 of the IC. On pressing this key, the above whole procedure is repeated, and we go on till we finish pressing the last key (code no.2), when ultimately a logic hi settles at pin 1, and the output stage is toggled ON through a relay. This out put may be used to grant access to whatsoever is connected to it.
  • Pressing of any key other than the coded ones will immediately reset the circuit, so getting access by trial and error will never succeed, making the whole system of this electronic combination lock perfectly foolproof.

Please refer the master combination lock circuit diagram in the Part 1 Section.