Device Switching Using Password

Posted on Feb 6, 2014

Here is a project Device switching using password by innovative group Dreamlover technology, lets the user to lock their device with password. The block diagram of device switching using password is shown in figure 1. As the circuit device switching using password send as well as receive data it is divided into two main section i. e. transmitter and receiver

Device Switching Using Password
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section (DTMF decoder and password setup section). Transmitter section: - The heart of the transmitter section (DTMF generator) is IC1 (UM91214B), the entire transmitter section is designed and fabricated around DTMF encoder IC (IC1). Cristal oscillator XTAL1 is used here for internal oscillation connected to pin 3 and 4 of IC1. The oscillated output is further converted into DTMF signal internally and as a result tone is obtained from pin 7 of IC1. ­ ­ ­ ­ ­ ­ ­ ­The 4 rows of keypad is connected to pin 15 to pin 18 of IC1, similarly 3 columns to pin 12 to pin 14 as shown in figure 2. Here, keys 1 through 9 is used to control the device, where key 0  is used to switch off the device and key *  is used to reset the circuit. The key #  is not used here. A unique pair of sine wave [i. e. dual-tone multi frequency (DTMF)] is produced whenever any key of keypad is pressed. The produced is of audible frequency range (i. e. 300 to 2400 Hz) but is so chosen that the possibility of interface with normal speech simultaneously is minimized. The produced tone is pair of lower frequency rows (697 Hz, 770 Hz, 852 Hz, 941 Hz) and higher frequency columns (1209 Hz, 1336 Hz, 1477 Hz or 1633 Hz) in order to minimized the problem of interface. We used here 11 unique combination of codes (tones) out of 16 allows by DTMF and are so chosen that none of the tones are harmonic in nature with each other. The output tone is available at pin 7 of...

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