Device Switching Using Password

Different security based project is published in Now, it’s time to be more secure. Here is a project “Device switching using password” by innovative group Dreamlover technology, lets the user to lock their device with password.

Circuit Description

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 section (DTMF decoder and password setup section).

block diagram of device switching using password

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 IC1, connected to point “A” of DTMF decoder circuit (IC2) as shown in figure 2.

circuit diagram of device switching using password

Receiver section:- The receiver circuit is further divided into two section i.e. DTMF decoder and password circuit.

The DTMF decoder:- For DTMF decoder we use here DTMF decoder IC KT3170 but we can also use MT8870 (IC2). A crystal oscillator is connected to pin 7 and pin 8 of IC2 for providing necessary clock for internal circuit of DTMF decoder. The binary output is obtained corresponding to the key pressed in the keypad of transmitter circuit.

Whenever any key is pressed in transmitter circuit a valid DTMF tone is received by IC2 which further decoded into 4-bit binary output available at pin 11 to 14 which further decoded into 4-bit binary output available at pin 11 to 14 of IC2. At the time of receiving tone pair delayed steering output (StD) pin 15 goes high which further pulse the clock pin of IC4 and IC5. Here, StD pulse is used to shift the data in dual 4-bit static shift register of IC4 and IC5.

Password Circuit:- The password circuit is build and fabricated by two dual 4-bit static register(IC4 and IC5) and EX-OR ICs (IC6 through IC9). Cross-checking or for checking whether the entered password is correct or not EX-OR gate is used (IC6 through IC9). The work of shift register is to store the password in binary form.

The setting of password is done by sliding the DIP switch (DIP1 to DIP4) connected to input of EX-OR gate.

When any key is pressed in keypad a binary code from IC2 is fed to shift register. Bit 1 to 4th bit is fed to shift register IC4 (A), IC4 (B), IC5 (A), IC5 (B) respectively. The shift register get clock from IC2 by StD pin 15 through AND gate N17.

The decimal number password is set by keypad where corresponding binary number are fed through the DIP switch. The password set by DIP switch along with data stored in IC4 and IC5, should result into a low output across the output of IC11 through IC13.

The output of gate N22 goes low when correct password is entered because the input of gate N22 is connected to output of gate N18 through N21 which further enable the demultiplexer (IC3) and appliance is turned on. As from the circuit diagram the output of gate N22 is connected to input of AND gate N17. As a result whenever the output of N22 is low the output of N17 is also low which further block clock to IC4 and IC5 (i.e. when password is correct no clock pulse is given to static register).

But when incorrect password is entered the output of N17 is high as well of N22 which pass the clock pulse to IC4 and IC5 and disable IC3 (demiltiplexer).

The first four digit entered is for password but fifth key is of appliance switch i.e. fifth decimal key is for the corresponding appliance, key 1 through 9 is used to energized relay RL1 through RL9 respectively. Key “0” is used to switch off the device where key “*” is used to reset the circuit.

Password Setting (Refer table): - Here is a method of password setting. Suppose if anyone want to setup the password “9765”. Digit 9, 7, 6 and 5 should press sequentially which further stored into shift register IC4 and IC5 in binary format.

1st binary digit (A bit) data stored in IC4(A) is 1101, so 1101 is set through DIP switch DIP1 by  making SW1 on (1), SW2 on (1), SW3 off (0) and SW4 (1).

Similarly, 2nd binary digit (B bit) data is stored in IC4(B) is 0110, so 0110 is set through DIP switch DIP2 by making  SW1 off (0), SW2 on (1), SW3 on (1), SW4 off (0).

3rd binary digit (C bit) data is stored in IC5 (A) is 0111, so 0111 is set through DIP switch DIP3 by making SW1 off (0), SW2 on (1), SW3 on (1), SW4 on (1).

4th binary digit (D bit) data is stored in IC5(B) is 1110, so 1110 is set through DIP switch DIP4 by making SW1 on (1), SW2 on (1), SW3 on (1), SW4 off (0).

Now, password is set and the circuit is ready to control appliance.

Password Setting Example


Decoder Output


Keypad No. Seq.





Register Output

























Reg. No.






 Fabrication: A single-side PCB design for "Device Switching Using Password" are shown below:

pcb design of devics switching using password

component layout of device switchining using password

pcb design of transmitter


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 330 Ω

R2 – R4 = 100 Ω

R5 = 330 KΩ

R6 – R14 = 4.7 KΩ


C1 = 10 µF/10V electrolytic

C2, C3 = 39 pF ceramic disk

C4, C5 = 0.01 µF ceramic disk


IC1 = UM91214B (DTMF dialler)

IC2 = KT3170/MM8870 (DTMF decoder)

IC3 = 75LS154 (4-to-16-line decoder / demultiplexer)

IC4, IC5 = CD4015 (dual 4-bit static shift register)

IC6 – IC9 = CD4030 (quad Exclusive-OR gate)

IC10 = 7408 (quad 2-input AND gate)

IC11 – IC13 = CD4072 (dual 4-input OR gate)

IC14 – IC15 = 74LS04 (HEX inverter)

D1 – D9 = 1N4007 (Rectifier Diode)

T1 – T9 = BC548 npn transistor

ZD1 = 3.3V zener diode


XTAL1, XTAL2 = 3.58 MHz Crystal oscillator

SW1 = ON/OFG switch

DIP1 – DIP4 = 4 way DIP switch


19 thoughts on “Device Switching Using Password”

  1. Thank you sir, for this project as i am student of diploma i don't have any concept of programming. I really appreciate because of your describing style.

    1. The project can mainly be used for basic locker systems and door locking systems.
      Beside these it can also be used on an array of different systems which requires devices to be accesed by only few members.

  2. Hi sir I am a student of MSc Electronics. i wana know that which type of devices i can controlled by this project because i wana make this project..

    1. The project used relay to switch devices.

      SO you can use it with preety much any device that can be swittched on and off.
      But for the purpose of demonstration , I suggest using it for door locking system.

  3. In the transmitter section the main IC used UM91214B is not available in my locality…. Can the circuiy be constructed using any other IC or in a different way

  4. Hi! Instead of the Demux, what should I use so that I can switch to device without it being off. So instead of having only 1 load being on, I can freely switch everything on and off. thanks.

  5. sir, can we also use it as a basic switch for a laser security alarm ,if we want to access our things that is in protection of it.

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