Frequency Shift Keying FSK Modulator Using IC 555

Frequency shift keying FSK modulator using IC 555 Gadgetronicx > Electronics > Circuit > Transceiver Circuits > Frequency shift keying FSK modulator using IC 555 Frank Donald August 2, 2013 12 Comments

Transceiver Circuits ic555

Frequency Shift Keying plays a great role in wide range of applications in the field of communication and was considered efficient one in data transmission of wireless modems.This above FSK modulator using IC 555 is capable of generating FSK signal with respect to the given input signal. The resistors Ra,Rb and C determines the frequency of the FSK modulated signal in the astable mode of operation. Also check out the matching FSK Demodulator using IC 565 circuit. Lets move into the working of this circuit.

WORKING OF FSK MODULATOR USING IC 555: The output frequency of the signal was based on the input digital signal given to the base of the transistor.When the given input was high that is of logic 1 the PNP transistor was Q is off and IC 555 timer works in the normal Astable mode of operation giving out the series of square wave pulses thus there will be no change in the frequency of the output signal.Here the resistors Ra, Rb and Capacitor C was selected in such a way to obtain output frequency of 1070Hz.The output frequency when the input was high was given by the equation f= 1.45/(Ra + 2Rb)C When the input binary data if logic 0, the PNP transistor is on and its connects the resistance Rc across resistance Ra.The resistors Rc is selected in such a way that the value of 1270Hz.Here the value of Rc added in addition to the Ra, Rb and C to contribute the working

of the NE555.This makes the charging and discharging quicker resulting in high frequency waves as output.The Ra, Rb, Rc and C values was selected in such a way to obtain output frequency of 1270 Hz.This was given by the equation f=1.45/((Ra || Rc)+ 2Rb)C Thus the resultant output FSK will give frequency of 1070Hz when input is high and frequency of 1270 when input is low.Thus by this way the FSK signal was obtained using NE555.

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Frank Donald Junior Network Engineer at Tata Communications

Frank Donald is an Electronics and Communication Engineer who loves building stuff in his free time. Video games, blogging and programming are the things he loves most ← Previous post Next post →

Ask your query 12 Comments on "Frequency shift keying FSK modulator using IC 555"

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7709071950 http://w w w .gadg

How I make the ASK modulator using ic-555

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2 months 16 days ago

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Frank Donald http://w w w .gadg

Hi, This might help you https://www.engineersgarage.com/electronic-circuits/ask-modulator-using-ic-555

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2 months 11 days ago

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Arjun http://w w w .gadg

Hello, I need some 200-300 Mhz output from 6-10 khz input. Is it possible to get from this circuit with resistors’ and capacitors’ values being changed??

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2 years 1 month ago

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Anonymous http://w w w .gadg

Are the Ra and Rc components resistors or potentiometers?

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2 years 3 months ago

Guest


Those are resistors, you can substitute with potentiometers if you need to alter the output frequency.

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Guest


so how can i change the circuit into an active high circuit with the f1 frequencies being higher then f2

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Manos ManolIs http://w w w .gadg

hello, what should be the mark and space frequencies if i want to apply digital voice input(at least at 8KHz), and how can i get them? thank you.

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Guest


As i said above you can alter the mark and space frequency based on your requirement by altering the component Ra,Rb,Rc and C values in the above circuit diagram. Only switching of the state between the mark and space frequencies will be rapid if you increase the frequency of the digital input.

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Guest


This circuit have 200Hz interval. I want 1KHz interval, Should i modify the capacitor C or C1 to obtain better result?

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Guest


200 Hz interval? Cant understand your point kindly brief a bit. The capacitor C1 was used to reduce to noise in the above circuit and there will be no impact in frequency due to this. If you are intend to change frequency you can alter the values of Ra, Rb and C above.

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Guest


You can use 2N2907 for the above circuit

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beat http://w w w .gadg

an what king of Q PNP can I use, is a lot of tipes on PNP

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Binary Frequency Shift Keying (BFSK) using 555 Timer 1 555 Timer, tutorials 8/09/2013 Frequency-shift keying (FSK) is a type of frequency modulation scheme in which the digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK (BFSK). BFSK transmits only the binary information of a message signal, zeros or ones.

Circuit Diagram

In Binary Frequency Shift Keying (BFSK) system, the carrier frequency is switched between two frequencies according to the binary input. The 555 timer functions in astable mode. The frequency of operation is given by the expression

Fo = 1.45/(Ra+2Rb)

If the resistor Ra varies, the frequency varies. When the input is at logic 1, the transistor turn ON and effectively resistance of Ra decreases, because transistor offers a resistance of a few ohms in parallel to Ra. This makes the frequency of operation less. The potentiometer Ra is used to fine tune the frequency. When the input is at logic 1, frequency of operation is given by the expression

Fo = 1.45/(Ra//R + 2Rb)

FSK Using 555-Timer

FSK Using 555-Timer

The astable multivibrator with selective frequency input gives FSK Frequency Shift Keying. We may manually change the frequency through a potentiometer, but if it has to be changed by a digital signal, this circuit can be used. By inserting a resistance in parallel to the existing timing resistors, the time period can be varied. This is done with the help of a transistor.

Waveform of FSK

This is not limited to a single parallel path, we can increase as many parallel resistors as required, provided there are enough inputs.

Pulse Width Modulation with modulating signal

Sinusoidal Pulse Width Modulation

The monostable multivibrator, with the modulating signal at the control voltage terminal, gives pulse width modulation according to the modulating signal. For this, the basic requirement is, pulse duration of mono-stable circuit should be far less than the time period of the modulating signal. The frequency of the Trigger input should be far higher than the modulating signal. This type of circuit is generally used in inverter design. Trigger input of about 20 KHz is used and the modulating signal will be sinusoidal at this power frequency. This is just a basic idea, but actual frequencies are obtained by lots of calculations to reduce harmonics and to produce the desired magnitude of voltage.

Sinusoidal Pulse Width Modulation

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Frequency Shift Keying FSK Modulator Using IC 555

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