3 Input Mic Mixer Circuit

Here is a simple 3 input mic mixer circuit using the popular uA 741 ICs. Four 741s are used here.IC1, IC2, IC3 are used as preamplifiers. They produce a gain of around 40 decibel to the individual input signals. The IC4 is wired as a summing amplifier to add the signals from three preamplifiers.IC4 also gives a gain of around 5decibel to the final output signal. Total gain of the system is around 45decibel.

Notes.

• Assemble the circuit on a good quality PCB.
• A +15/-15 V DC dual power supply is needed for powering the circuit.
• All inputs and output must be connected with respect to the ground.
• ICs must be mounted on holders.
• Electrolytic capacitors C1, C2 and C3  must be rated 10V and other capacitors  must be 30V.

Musical Bell (UM 66)

This circuits uses very few component and gives melody sound. It uses 3 terminal IC UM66 and can be build small enough to be placed inside a greeting card and operated off a single 3V flat button cell.

There is not much to the circuit. The UM66 is connected to its supply and its output fed to a transistor for amplification. Any common speaker can be used or a “flat” piezoelectric tweeter like the one found in alarm wrist watches. If you use the piezo, then it can be connected directly between the output pin 1 and ground pin 3 without the transistor.

The UM66 looks like a transistor with 3 terminals. It is complete miniature tone generator with a tune. Now they come with wide variety of different tunes.

For amplification we have used a NPN transistor which is BC548. Here BC548 makes a common emitter circuit. For limiting the base current we have used a resistance of 220 Ohms so that transistor will not get damaged by excess current.

PROCEDURE :

1. Draw circuit diagram on ply board and make hole with compass or broader for component pin insertion.

2. Identify emitter base collector of transistor and pin no. of IC UM66

3. Solder all parts according to the circuit. You will need soldering iron, Soldering flux and flexible wire.

4. Make sure all points are well soldered according to the Circuit Diagram and no dry solders. Wrong connection of IC may heat up and get damage.

5. After loading battery power ON the circuit. Now you can check the function of the project.

OR

• D400 - 1
• UM66 - 1
• 1k - 1
• speaker - 1

With an integrated series UM66TXX can get different melodies that are attached to the table.

The Universal Timer

Now, a day automation task is necessity not only in industrial sphere but even in the domestic sphere.

The project universal timer in this website is unique because it offer an ultra wide range of time period having pin point precision anywhere (i.e. not affected by ant physical factor) from one – tenth of a second to hundreds of hours. Due to feature “auto latch” facilities and low power consumption CMOS IC used plus such a low current consumption on that most multimeter would fail to detect it. The above facility with low costlier and familiar design make the circuit “The Universal Timer ” more versatile.

Circuit description of universal timer

High frequency signal of several kilohertz is generated by IC1 CD4060, and VR1 is used to remove device imprecision errors. The internal frequency divider of IC1 divides the base frequency by a factor of 213 times i.e. 16384 times.

The output frequency of 10 KHz from pin 3 of IC1 is simultaneously divided by set of five CD4017 counters (IC2 – IC6) by 10, 6, 10, 6, and 10. Here IC2 to IC6 is configuring in maximum mode and divided-by-six decimal mode respectively where output is selected by range selector switch SW1.

The output time period from range selector of universal timer switch is 0.1 second, 1 second, 0.1 minute, 1 minute, 0.1 hour, 1 hour respectively given to two serial connected counter CD4017 (IC7, IC8). The outputs from range selector provide precise master clock frequency, counted by IC7 and IC8. IC7 and IC8 counts one and ten master pulses respectively.

The timer section of universal timer is control by two rotator switch SW2 and SW3 as shown in circuit diagram figure 1.

NAND gate N1 is used to change the state of output from SW2 and SW3. The feedback diode D1 helps to latches the next NAND gate N2.

Lastly a relay driver transistor T1 is used to drive relay connected to collector of transistor T1. The relay contacts can be selected to switch the load ‘ON’ or ‘OFF’ after the preset time. Switch SW4 (Push-To-On switch) is used to reset the whole circuit. Power supply interruption also reset the entire circuit of universal timer.

NOTE: Connect a device to a timer and set it to short period, say a few seconds, and adjust VR1 till exactly that time delay is obtained. The accuracy on rest of the range will follow automatically.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R1 – R4, R10, R11 = 1 KΩ

R5, R6 = 10 KΩ

R7 = 47 KΩ

R8 = 24 KΩ

R9 = 100 Ω

VR1 = 4.7 KΩ

Capacitors

C1 = 0.0001 µF ceramic

C2 = 100 µF/25V electrolytic

Semiconductors

IC1 = CD4060

IC2 – IC8 = CD4017

IC7 (N1 – N2) = CD4011

T1 = BC547 NPN transistor

D1 – D3 = 1N4148

Miscellaneous

SW1 = Single–pole 6–way rotary switch

SW2, SW3 = Single–pole 10–way rotary switch

SW4 = Push-To-On switch

SW5 = On/Off switch

SW6 = SPDT (Single pole double throw)

RL1 = 300 Ω 12V relay

LED1 = RED

LED2 = Green

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