It was standardized when the dual-tone multi-frequency signaling (DTMF) system was developed in the Bell System in the United States in the 1960s that replaced rotary dialing originally developed in electromechanical switching systems. Note: Use button “R” (Reset) for deactivating the relay or to re-enter the password in case you entered an incorrect password.A telephone keypad using the ITU E.161 standard.Ī telephone keypad is a keypad installed on a push-button telephone or similar telecommunication device for dialing a telephone number. You can rearrange the wiring of the buttons at pin numbers 3, 2, 4, 7 and 10 of IC 4017 and don’t change the number order on the keypad which is illustrated on the keypad layout diagram. The default password is “21345” only if you match the push button’s number on the circuit diagram with the keypad layout’s number. To change the password, you need to make changes to your circuit setup physically, since there no involvement of microcontroller or software. How to set a new password / change password: In conclusion there are two layers of security, the first one is password that must be entered in the correct sequence only then the relay gets activated, the other layer is decoy buttons.Įven when someone is able to guess the first few numbers correctly, pressing any one decoy button will reset the IC which makes the first few correct pin numbers useless. When an unauthorized person tries to guess the password there is a very high probability that he / she may press one of the decoy buttons while guessing which will reset the IC. The above mentioned process works only if the correct buttons are pressed in the correct sequence, otherwise the relay will not turn ON. When you press the button connected to pin #10, which is the last digit of your password, the output Q5 – pin #1 turns high which turns on the transistor and triggers the relay ON.
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