26-08-2013, 04:25 PM
8-digit code lock for appliance switching
8-digit code lock.pdf (Size: 117.92 KB / Downloads: 44)
This code lock is useful for appliances requiring exclusive or authorised use by those who know the preset code. If desired, the code can be changed. DIP switches. The code is set using DIP switches DIP3 and DIP4. Then these two
switches are hidden inside the assembly. With DIP3 and DIP4, up to 256 code com- binations are possible. The unlocking code is set by the user using DIP switches DIP1 and DIP2, which is compared with the preset code entered earlier via DIP3 and DIP4. If the two codes match, transistor T1 conducts. The codes are compared using two cascaded 4-bit magnitude comparator ICs (IC1 and IC2). If the input nibble pres- ent at DIP1 matches with preset DIP3 nibble, output pin 6 of IC1 (connected to input pin 3 of IC2) goes high. Now if
nibble present at DIP2 matches with the preset nibble at DIP4, pin 6 of IC2 also goes high. This high output drives transistor T1 and the appliance turns on via relay contacts.