Schematic & Wiring Diagram

The agenda lock apparent beneath uses 4 accepted argumentation ICs to acquiesce authoritative a broadcast by entering a 4 chiffre cardinal on a keypad. The aboriginal 4 outputs from the CD4017 decade adverse (pins 3,2,4,7) are gated calm with 4 digits from a keypad so that as the keys are depressed in the actual order, the adverse will advance. As anniversary actual key is pressed, a low akin appears at the achievement of the bifold NAND aboideau bearing a aerial akin at the achievement of the 8 ascribe NAND at pin 13.

The cursory aerial akin from pin 13 activates a one attempt ambit which applies an almost 80 millisecond absolute activity beating to the alarm band (pin 14) of the decade adverse which advances it one calculation on the ascent edge. A added monostable, one attempt ambit is acclimated to accomplish an almost 40 millisecond absolute activity beating which is activated to the accepted point of the keypad so that the adapted NAND aboideau will see two argumentation aerial levels back the actual key is apprenticed (one from the adverse and the added from the key). The astern alarm beating (negative going) at pin 12 of the 74C14 and the absolute activity keypad beating at pin 6 are gated calm application two diodes as an AND aboideau (shown in lower appropriate corner). The achievement at the alliance of the diodes will be absolute in the accident a amiss key is apprenticed and will displace the counter.

Back a actual key is pressed, outputs will be present from both monostable circuits (clock and keypad) causing the displace band to abide low and acceptance the adverse to advance. However, back the keypad beating begins hardly afore the clock, a 0.1uF capacitor is affiliated to the displace band to adjournment the displace until the astern alarm arrives. The ethics are not analytical and assorted added timing schemes could be acclimated but the alarm arresting should be hardly best than the keypad beating so that the alarm arresting can affectation out the keypad and abstain resetting the adverse in the accident the alarm beating ends afore the keypad pulse. The fifth achievement of the adverse is on pin 10, so that afterwards four actual key entries acquire been made, pin 10 will move to a aerial akin and can be acclimated to actuate a relay, brighten an LED, ect. At this point, the lock can be displace artlessly by acute any key.

The circuit can be continued with added gates (one added CD4011) to acquire up to a 8 chiffre code. The 4017 counting adjustment is 3 2 4 7 10 1 5 6 9 11 so that the aboriginal 8 outputs are affiliated to the NAND gates and pin 9 would be acclimated to drive the broadcast or light. The 4 added NAND aboideau outputs would affix to the 4 actual inputs of the CD4068 (pins 9,10,11,12). The ambit will accomplish from 3 to 12 volts on 4000 alternation CMOS but alone 6 volts or beneath if 74HC genitalia are used. The ambit draws actual little accepted (about 165 microamps) so it could be powered for several months on 4 AA batteries bold alone alternate use of the relay.