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Five Band Graphic Equalizer electronic Circuit

Equalization is the process of adjusting the balance between frequency components within an electronic signal.In the graphic equalizer, the input signal is sent to a bank of filters. Each filter passes the portion of the signal present in its own frequency range or band. The amplitude passed by each filter is adjusted using a slide control to boost or cut frequency components passed by that filter. The vertical position of each slider thus indicates the gain applied at that frequency band, so that the knobs resemble a graph of the equalizer’s response plotted versus frequency.here we see 5 band graphic equalizer circuit.

five band graphic equalizer using IC

This circuit uses a single chip, IC BA3812L for realizing a 5 band graphic equalizer for use in hi-fi audio systems.The BA3812L is a five-point graphic equalizer that has all the required functions integrated onto one IC. The IC is comprised of the five tone control circuits and input and output buffer amplifiers. The BA3812L features low distortion, low noise, and wide dynamic range, and is an ideal choice for Hi-Fi stereo applica-tions. It also has a wide operating voltage range (3.5V to 16V), which means that it can be adapted for use with most types of stereo equipment.

The five center frequencies are independently set using external capacitors, and as the output stage buffer amplifier and tone control section are independent circuits, fine control over a part of the frequency bandwidth is possible, By using two BA3812Ls, it is possible to construct a 10-point graphic equalizer. The amount of boost and cut can be set by external components.

The recommended power supply is 8V, but the circuit should work for a supply of 9V also. The maximum voltage limit is 16V.

The circuit given in the diagram operates around the five frequency bands:

  • 100Hz
  • 300Hz
  • 1kHz
  • 3kHz
  • 10kHz


The transmitter for the wireless headphones is built around a CD4046 CMOS phase-locked loop, coupled with a driver transistor, and a pair of infrared LEDs.
Although the CD4046 is comprised of two phase comparators, a voltage-controlled oscillator (or VCO), a source follower, and a zener reference, only its VCO is used in this application.


Wireless Ir headphone Transmitter


Audio input from PL1 frequency modulates the VCO section of a 4046 PLL chip. The VCO output drives Q1, a switching transistor. Q1 drives two IR LEDs. The signal produced is around 100 kHz, FM carrier VCO sensitivity is around 7.5 kHz/V.

Sawtooth Wave Generator

What is sawtooth wave generator?

The sawtooth wave (or saw wave) is a kind of non-sinusoidal waveform. It is named a sawtooth based on its resemblance to the teeth on the blade of a saw.

Click the image to enlarge…..

Sawtooth wave generators using OP-Amp are very common. But the disadvantage is that it requires a bipolar power supply.

A sawtooth wave generator can be built using a simple 555 timer IC and a transistor as shown in the circuit diagram.

The working of the circuit can be explained as follows:
The part of the circuit consisting of the capacitor C, transistor,zener diode and the resistors form a constant current source to charge the capacitor. Initially assume the capacitor is fully discharged. The voltage across it is zero and hence the internal comparators inside the 555 connected to pin 2 causes the 555’s output to go high and the internal transistor of 555 shorting the capacitor C to ground opens and the capacitor starts charging to the supply voltage. As it charges, when its voltage increases above 2/3rd the supply voltage, the 555’s output goes low, and shorts the C to ground, thus discharging it. Again the 555’s output goes high when the voltage across C decreases below 1/3rd supply. Hence the capacitor charges and discharges between 2/3rd and 1/3rd supply.

Note that the output is taken across the capacitor. The 1N4001 diode makes the voltage across the capacitor go to ground level (almost).

The frequency of the circuit is given by:

f = (Vcc-2.7)/(R*C*Vpp)


Vcc= Supply voltage.
Vpp= Peak to peak voltage of the output required.

Choose proper R,C,Vpp and Vcc values to get the required ‘f’ value.

Intercom using Transistor

What is Intercom???

An intercom (intercommunication device), talkback or doorphone is a stand-alone voice communications system for use within a building or small collection of buildings, functioning independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles. Intercoms can incorporate connections to public address loudspeaker systems, walkie talkies,telephones, and to other intercom systems. Some intercom systems incorporate control of devices such as signal lights and door latches.

here we are going to see about how the intercoms are made using transistors..Circuit diagram is given below

Click the image to enlarge…

The circuit comprises a 3-stage resistor-capacitor coupled amplifier. When ring button S2 is pressed, the amplifier circuit formed around transistors T1 and T2 gets converted into an asymmetrical astable multivib-rator generating ring signals. These ring signals are amplified by transistor T3 to drive the speaker of earpiece.
Current consumption of this intercom is 10 to 15 mA only. Thus a 9-volt PP3 battery would have a long life, when used in this circuit.
For making a two-way intercom, two identical units, as shown in figure, are required to be used. Output of one amplifier unit goes to speaker of the other unit, and vice versa. For single-battery operation, join corresponding supply and ground terminals of both the units together.
The complete circuit, along with microphone and earpiece etc, can be housed inside the plastic body of a cellphone toy, which is easily available in the market. Suggested cellphone cabinet is shown.

Base-treble tone Control circuit

Click the image to enlarge

The LM1036 is a DC controlled tone (bass/treble), volume and balance circuit for stereo applications in car radio, TV and audio systems. An additional control input allows loudness compensation to be simply effected. Four control inputs provide control of the bass, treble, balance and volume functions through application of DC voltages from a remote control system or, alternatively, from four potentiometers which may be biased from a zener regulated supply provided on the circuit. Each tone response is defined by a single capacitor chosen to give the desired characteristic.


  • Wide supply voltage range, 9V to 16V
  • Large volume control range, 75 dB typical
  • Tone control, �15 dB typical
  • Channel separation, 75 dB typical
  • Low distortion, 0.06% typical for an input level of 0.3 Vrms
  • High signal to noise, 80 dB typical for an input level of 0.3 Vrms
  • Few external components required

Note: Vcc can be anything between 9V to 16V and the output capacitors are 10uF/25V electrolytic.


Infra Red Headphones

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Using this low-cost project one can reproduce audio from TV without disturbing others. It does not use any wire connection between TV and headphones. In place of a pair of wires, it uses invisible infrared light to transmit audio signals from TV to headphones. Without using any lens, a range of up to 6 metres is possible. Range can be extended by using lenses and reflectors with IR sensors comprising transmitters and receivers.
IR transmitter uses two-stage transistor amplifier to drive two series-connected IR LEDs. An audio output transformer is used (in reverse) to couple audio output from TV to the IR transmitter. Transistors T1 and T2 amplify the audio signals received from TV through the audio transformer. Low-impedance output windings (lower gauge or thicker wires) are used for connection to TV side while high-impedance windings are connected to IR transmitter. This IR transmitter can be powered from a 9-volt mains adapter or battery. Red LED1 in transmitter circuit functions as a zener diode (0.65V) as well as supply-on indicator.
IR receiver uses 3-stage transistor amplifier. The first two transistors (T4 and T5) form audio signal amplifier while the third transistor T6 is used to drive a headphone. Adjust potmeter VR2 for max. clarity.
Direct photo-transistor towards IR LEDs of transmitter for max. range. A 9-volt battery can be used with receiver for portable operation.