Three in one Tone Generator

Various tone generator circuit is already published in Now, here is unique tone generator circuit which produces three different type of sound according to input three different logic levels (i.e. 0&1, 1&0 and 1&1).

Circuit description

This circuit is designed around digital IC 7400 which is NAND gate. The working of the circuit is like the working principle of oscillator circuit, where frequency depends upon capacitors C1 and C2. The duty cycle of this circuit is 50%. The output is given to power amplifier circuit which further drive loudspeaker or head phone. For low frequency value of capacitor C1 and C2 must be high and vice-versa.

circuit diagram of three tone generator


Resistors (all ¼-watt, ± 5% Carbon)

R1, R4 = 1.2 KΩ

R2, R3 = 1 KΩ

R5 = 10 KΩ

R6, R7 = 47 KΩ


C1 = 100 kpF

C2 = 220 kpF

C3, C4 = 10 kpF


IC1 = 7400 (NAND gate)

D1, D2 = 1N4148

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


Electronics counter

Simple counting can be done by anyone but counting in interval up to large number is tedious and the chance of forget is maximum. As, we have already published Counter Circuit | Digital Counter. Now , here electronics counter is second project by dreamlover technology in the series of counting based project. Bothe the counting circuit published in this website counts up to 10,000 with the help of four seven-segment displays. The difference is previous circuit utilize CMOS ICs where the electronics counter use TTL ICs.

Circuit description

The entire circuit of electronics counter is divided into three main section :- input, display and driver or decoder section.

The input circuit consists of LDR following by negative square wave generator circuit build around Timer IC (NE555). A bulb is used here as light source focused on LDR. The property of LDR is that whenever the light focused on base of LDR is obstructed, it gives trigger and square wave is generated and given as input signal to counter circuit. So the objects to be counted are arranged in a row to move one by one in between the light source and the LDR.

 circuit diagram of ldr operator

IC2 shows any number between 0-9 according to input square wave given to pin no 14. After each negative pulse a carrying pulse is produced by decoder IC and given to another one (i.e. from IC2 to IC3, IC3 to IC4, IC4 to IC5 ). IC5­ and IC6 is BCD to 7-segment latch decoder driver. The reset switch SW1 is used to reset the electronics counter to 0000 states.

circuit diagram of electronics counter decade counter

Resistors (all ¼-watt, ± 5% Carbon)

R1 = 1 KΩ

R2 = 100 KΩ

R3 – R30 = 180 Ω

VR1 = 100 KΩ preset


C1 = 4.7 µF

C2 = 1000 µF/10V

C3, C4 = 0.1 µF


IC1 = NE555 (Timer IC)

IC­2 – IC5 = 7490 (Decade and Binary counter)

IC6 – IC9 = 7447 (BCD to 7-segment decoder)

IC10 = µA 7805 (Voltage Regulator)

D1 – D­4 = Display FND 507


Mic1 = Microphone

B1 = Bulb




Related Project

  1. Advanced LED Temperature Indicator use of a V/F converter in monitoring temperature in degrees Fahrenheit (0F).
  2. Counter Circuit | Digital Counter Counter using CMOS ICs , counts up to 10000
  3. Twilight Lamp Blinker indicate obstruction by blinking in adjusted time
  4. Multi-Mode Running Light used in ceremony, can operate in three different mode
  5. Digital Mains Failure/Resumption Alarm indicating AC mains fails or resumes by producing alarm sound

Versatile Digital Teste

It is difficult to detect the fault and troubleshooting digital circuits. Here is a simple and versatile circuit of digital tester for detection of condition of the components and also indicates the nature of defect.

Circuit description of versatile digital tester

This whole circuit of versatile digital tester is designed and fabricated around CMOS hex inverter buffer CD4049 containing six independent inverters (a – f). Where inverter (a) form basic integrator. Inverter B and C form the Schmitt trigger. Preset VR1 & VR2 is used to controls the frequency of the square wave oscillator and adjust the duty cycle to 50% respectively. The output of each inverter is fed to another inverter. Inverters d with e produce complementary output. A.C. output is obtained from complementary pair (inverter d and e) used to drive two LEDs (LED1 and LED2) where resistor R6 is used as current limiter of LEDs.

Inverter f is designed to detect logic state where LED3 and LED4 indicate high and low logic state respectively and is depends upon logic condition at probe P5 with respect to probe P6. Transitional point (where the LEDs just switch off) is adjusted by preset VR3.

Generated frequency from versatile digital tester is taken from probe P1 and P2 and is set by preset VR1 where frequency range of 10 Hz to 1 KHz in LF position and 1 KHz-70 KHz in HF position. The LF and HF position is decided by switch SW1­.

Probe P3 and P4 is used to test semiconductor and its direction (forward bias and reverse bias). The forward bias of semiconductor is decided with LEDs direction. Either glowing LED indicates functional order and polarity. Resistive component can also be tested through probe P3 and P4, glowing both LEDs indicate component is functioning.

Probe P5 and P6 is used to test logic state where probe P6 is connected to ground of the circuit under test. Supply voltage must be 6V.

digital all in one tester


Resistors (all ¼-watt, ± 5% Carbon)

R1,R5, = 10 KΩ

R2 = 8.2 KΩ

R3 = 18 KΩ

R4 = 330 Ω

R6, R7 = 560 Ω

R8 = 680 Ω

VR1 = 2.2 MΩ

VR2 = 2.2 KΩ

VR3 = 220 KΩ


C1 = 0.033 µF

C2 = 390 pF

C3 = 3.3 pF


IC1 = CD4049B


SW1 = Single pole double throw (SPDT) switch

SW2 = Push to ON/OFF switch

LED1 – LED4 = Different Color LEDs



Related Project

  1. Noise Meter measure the level of noise indicating by LED, warning alarm after crossing the safe level
  2. Ohm Meter measuring the low resistance range form 0 to 1 and and 0 to 10.
  3. Test a Diode | Zener Diode tests the diode as well as zener diode 
  4. IC tester tester for timer IC 555 And Op-Amp IC 741
  5. Timer IC Tester check IC NE555 whether it have fault or not

Duty Cycle Selector

Here is a unique project, duty cycle selector because duty cycle of pulse generated by this circuit can be varied from 10% to 90% in different 9 steps in the difference of 10%. The two complementary outputs and the sum of their duty cycle is always 100% make duty cycle selector more versatile.

Circuit description of duty cycle selector

The duty cycle selector circuit only two low cost CMOS ICS (CD4001 and 4017). The NAND gate N1 with N2 is configured as oscillator and generate frequency (ten times of output frequency) is given to pin 14 of IC2. IC2 divides the input frequency by a factor of 10. The output frequency is determined by oscillator and be in range between 0.1 Hz to 50 KHz.

The value of generated frequency is determined by the formula

F = 1/2.2R2C1.

This formula is only verified when R1 = R2 and the value of R1 is not less than 10 KΩ


Resistors (all ¼-watt, ± 5% Carbon)

R1 = R2 > 10KΩ

C1 = Determined by output frequency


IC1 = CD4001

IC2 = CD4017


SW1 = 9-way rotary switch

Digital Nocturnal Nuisance

Here is a fun project “digital nocturnal nuisance” which is quite amusing for both children as well as elder too. Digital nocturnal nuisance produces irritating sound in the absence of light.

Circuit Description of digital nocturnal nuisance

Digital nocturnal nuisance circuit is designed and fabricated around quad 2-input NAND gate IC and a timer 555 IC. LDR in this circuit is used as sensor.

Two trigger circuits of nocturnal nuisance are made from four NAND gates N1 & N2­ and N3 & N4 connected in series. Timer IC (IC2) is configured as oscillator and generate audio frequency.

High trigger due to low resistance (presence of light) of LDR at input of N1 switch on the transistor T1 as a result capacitor C1 discharge through R7. Due to this input at second trigger circuit becomes low. Similarly, when the low input due to high resistance across LDR (absence of light) turn of the transistor T1 and capacitor C1 get charged through resistor R7 and logic of second trigger circuit (N3 and N4) becomes 1 and high input is given to pin 4 of IC2 which produce irritating sound.

Preset VR1 is used to adjust the sensitivity and is so adjusted that the input of N1 are at logic zero when the light is off.

Capacitor C1 and C3 is act as time changing and tone changing component respectively of digital nocturnal nuisance.


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 4.7 MΩ

R2, R6 = 10 MΩ

R3 = 10 KΩ

R4, R5 = 1 KΩ

R7 = 100 Ω

R8, R9 = 20 KΩ

R10 = 150 Ω

VR1 = 47 KΩ


C1 = 100 µF/16V

C2 = 100 nF

C3 = 15 nF


IC1 = CD4011 (quad 2-input NAND gats)

IC2 = NE555 (Timer IC)

T1 = BC108



LS1 = 8Ω speaker

Multi-Mode Running light

Running light based project is very interesting and one of the most made project. We use this type of project in many ceremony. Here is a unique project “Multi-Mode running light” in the series of LED based project because it can operate in three different modes.

Circuit description of multi mode running light

The whole circuit multi mode running light is designed and fabricated around timer IC and BCD UP-DOWN counter IC.

IC1 and IC2 is used to generate vary low and low frequency square wave respectively where output of IC1 is connected to different point (SW1) and is used when running light is working in differential modes and output of IC2 is connected to input of BCD-up-down counter IC 4510B (IC3) for producing sequential BCD output.

Outputs from IC3 is given to input pin of IC4 (BCD-to-decimal decoder 4028B) in order to decode the output from encoder IC (IC3). The ten outputs from IC4 are obtained and each output is connected to base of driver transistor in order to supply gate current to triac.

Here in circuit diagram of multi mode running light we show only one triac firing circuit because of complicated design. But similar triac firing circuit can be connected to each remaining output.

Variable resistor VR1 and VR2 is used to control period of interruption and period of running respectively where the direction of running light can be changed by mean of switch SW2.

multi mode running light


Resistors (all ¼-watt, ± 5% Carbon)

R1, R2 = 4.7 KΩ

R3 = 10 KΩ

R4 = 270 Ω

VR1, VR2 = 1 MΩ

VR3 = 100 KΩ


C1 = 10 µF/16V

C2, C4 = 0.01 µF

C3 = 4.7 µF/16V


IC1 IC2 = NE555

IC3 = CD4510B (BCD up-down counter)

IC4 = CD4028B (BCD-to-decimal decoder)

T1 = BC109

D1 = 1N4001

TR1 = 4A/400V


SW1 (a, b) = 2-pole 3-way switch

SW2 = single-pole 2-way switch

B1 = Bulb

Clap operated Remote Control for Fans

Here is the circuit of clap-operated remote control fans is used to control not only switching properties but also control speed of fan. The main advantage of clap operated remote control for fan is, it can control up to ten-step speeds of fan where normally a fan has three to five step speeds.

Circuit description clap operated remote control for fan

This entire circuit clap operated remote control for fan is divided into four major section i.e. sound-operated trigger pulse generator, clock pulse generator, clock pulse counter and load operator.

Sound-operated trigger pulse: – The heart of this section is transistor T1 BC148, configured as class-C amplifier mode. The MIC1 is used to change voice signal into its corresponding electrical signal and is given to base of transistor T1 in order to amplify and increase its intensity.

Clock pulse generator:- This section is build around timer IC NE555 and configured as monostable multivibrator. The trigger pulse generated by transistor T1 is given to pin 2 of IC1 and time period (T) for output high is calculated by formula.

T = 1.1RC

Clock Pulse counter:- This section is build around decade counter CD4017BC which counts the clock pulse generated by timer IC (IC1). The output from IC1 is given to pin 14 of IC2. IC2 has ten outputs, viz, o, 1, 2, 3, 4…..9. Here we use only three outputs i.e. output 1, 2 and 3 from pin 2, 4, and 7 respectively. Output 4 from pin 10 is directly connected to reset pin 15.

Load operator:- This section is build around three transistor as relay driver to operate three separate relay. Output from each pin of IC2 is given to base of each transistor through 100Ω and LED as shown in circuit diagram. Output is taken from collector of transistor and is connected to relay. The three LEDs used to indicate gear or speed i.e. LED1, LED2 & LED3 indicates gear 1, gear 2 & gear 3 respectively.

Clap switch



NOTE:-This circuit used to operate in 1st speed similarly, 2nd clap for 2nd speed, 3rd clap for 3rd speed and 4th clap to switch off the fan.


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 10 KΩ

R2 = 1.2 MΩ

R3 = 2.2 KΩ

R4 = 150 KΩ

R5 = 220 KΩ

R6 = 10 KΩ

R7, R8, R9 = 100 Ω


C1, C2 = 0.1 µF/16V

C3 = 4.7 µF/16V

C4 = 0.01 µF (ceramic disc)

C5 = 1000 µF/12V


IC1 = NE555 (Timer IC)

IC2 = CD4017BE (decade counter)

T1 = BC148

T2, T3, T4 = BEL187

D1, D2 = 1N4001 silicon diode


MIC1 = Condenser microphone 34LOD

LED1 = Green

LED2 = yellow


6V-0V-6V, 500mA secondary transformer

Twilight Lamp Blinker

It is very difficult to indicate any obstruction in day time. So to overcome this type of problem the team of dreamlover technology design a cirucit simple and inexpensive twilight lamp blinker,which blinks and can be used near obstructions.

Circuit Description of twilight lamp blinker

The entire circuit of twilight lamp blinker is designed and fabricated around LDR (Light Detector Resistor) and IC CD4093 (IC1). The preset VR1 is used to control brightness. For sensor LDR1 is used that has a high resistance during night (i.e. dark) and a low resistance at day time (i.e. light). The NAND gates (N3 and N4) of IC1 is used as oscillator where high input from NAND gate (N1) makes the output of NAND gate (N2) low and vice-versa. The high at NAND gate N2 result LED1 blinks by conducting transistor T1 where transistor T1 is the LED driver transistor. For more brightness more LEDs is connected parallel to LED1.


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 10 KΩ/10W

R2 = 1 MΩ/1W

R3 = 100 KΩ

R4­ = 100 Ω

VR1 = 100 KΩ


C1 = 0.68 µF/400V

C2 = 100 µF/40V

C3 = 10 µF/35V


IC1 (N1 – N4) = CD4093

T1 = BC547

D1, D2 = 1N4007

ZD1 = 5.6V/1W

ZD2 = 15V/1W


LED1 = Blinker

LDR1 = Light Detector Resistor

Battery = 4.8 V/500 mAh battery pack

SW1 = SPST (Single Pole Single Throw)

Digital Mains Failure/Resumption Alarm

AC mains fails when over load is connected and this problem is common in now days. Here is the simple circuit using optocoupler Digital Mains failure and resumption alarm, for indicating AC mains fails or resumes by producing alarm sound.

Circuit Description of digital mains failure alarm

The circuit digital mains failure alarm is build around optocoupler. The resistor R1, capacitor C1 & C2, with diode D1 &D2 provide sufficient voltage to glow internal LED of optocoupler. Here the IC2 CD4011 is used as oscillator to generate low frequency of 0.662 Hz to 1.855 KHz controlling with preset VR1. Audio sound is generator by timer IC NE555 (IC2). The generated frequencies from IC2 vary from 472 Hz to 1.55 KHz controlling with preset VR2. For sensing mains fails position of switch SW1 to point 1 and for sensing mains resumption change the position of switch SW1 to point 2.


Resistors (all ¼-watt, ± 5% Carbon)

R1, R4 = 1 KΩ

R2, R5 = 10 KΩ

R3 = 22 KΩ

VR1 = 50 KΩ

VR2 = 47 KΩ


C1 = 0.22 µF

C2 = 1 µF/16V

C3, C4 = 10 µF/16V

C5 = 0.04 µF

C6 = 0.01 µF

C7 = 100 µF/16V

C8 = 470 µF/16V


IC1 = MCT2E (optocoupler)

IC2 (N1-N3) = CD4011

IC3 = NE555 (Timer IC)

D1, D2, D3 = 1N4001


SW1 = SPDT (Single Pole Double Throw) Switch

SW2 = ON/Off Switch

LS1 = 8Ω/0.5W

9V Battery