Simple IR audio link

john April 7, 2010 100 Comments

Description.

Here is a simple IR audio link that can be used to transmit audio signals up to 4 meters. The signal to be transmitted is applied to the base of Q1 via resistor R4.The transistor Q1 drives the IR transmitting diodes D1 and D2.The audio input will be modulated to the IR signals transmitted.
The transmitted IR signals will be picked by the photo transistor Q2.The emitter voltage of the transistor Q2 will change according to the sound modulated to the IR signal. The transistors Q3 and Q4 amplifies this signal to drive the speaker or headphone.C1 and R3 forms a filter to avoid interference from stray IR signals.

Circuit diagram with Parts list.

ir-audio-link-circuit

Notes

The circuit can be assembled on a general purpose PCB.

Use 9V PP3 batteries for powering the transmitter and receiver.

The phototransistor Q2 can be any NPN phototransistor like PNZ154, PNA1605F, BPW77NA or BPW85.

An 8 Ohm speaker or a headphone can be used to hear the sound.

Comments
  • saad
    April 17, 2015

    Kindly tell me that where is the base of photo transistor to be attached?

  • alok
    April 14, 2015

    Ye receiver circuit galt h audio play nhi hoga bus signals send hoge or plzz aise post daal k dusro ka time waste na kro

  • sen
    March 12, 2015

    can I use LDR instead of phototransistor? thank you 🙂

  • January 6, 2015

    how many watts will this circuit produce

  • sooraj
    December 4, 2014

    what does mean audio in & audio out.

  • ahmad
    August 4, 2014

    Hi,I want to use this transmitter and receiver to send a data,data is not sound and is straem of ones and zeros bits. is it possible?! and is it possible to use 5 volt for power.beacause I want to use it in usb system.thanks for ur answer.

  • Hassam
    August 4, 2014

    sir plz help me how to identify pins of 3 pin photo transistor? ?

  • naane
    July 14, 2014

    sir, can connect microphone directly to the audio input?

  • February 13, 2014

    sir, is the circuit above simulated on breadboard or in proteus? have you build it already? is it working?

  • girish
    January 18, 2014

    can i use tsop1838 phototransistor….please replay.

  • naane
    November 23, 2013

    sir,i have small confusion in the circuit that,i have 1 micro f 6.3V CAPACITOR AND 1 micro f 63V CAPACITOR and 1 micro f 100V CAPACITOR,which is the capacitor used in receiver circuit.

    • Seetharaman
      January 19, 2014

      iUf 63 volts can be used. tsop1838 cannot be used. use only the listed photo transistors

  • November 23, 2013

    is their circuit has 2 IR DIOD ? to transmit the signal ???? if its true then what is the value of ir Diod ?????????

    • Seetharaman
      November 25, 2013

      TIL38 IR diodes which are freely available can be used. Two are used for better radiation pattern.

  • October 16, 2013

    sir,
    how can we give the input to the circuit

    • November 23, 2013

      u can use popo3 9v transistor battery and the process of supply

      1) 1st broken a popo3 9volt battery for getting the lied of jack point of popo3 battery
      2) solar wire with this jack which u got by broken the battery and out a positive lid and a negative then
      3) other end of the were solder the wire into circuit ,
      4) and connect with another popo3 battery which this new jack which u made by broken and soldering wire by a popo3 battery

  • narasimha
    October 16, 2013

    sir is there any modifications in receiver part

  • Shaik Allabakshu
    October 11, 2013

    sir instated of using Q1 if we can use microphone

  • narasimha rao
    October 5, 2013

    sir can you please explain how modulation takes place.
    thanks in advance

  • narasimha rao
    October 5, 2013

    sir can you explain how the current moves in the transmitter circuit .thanks in advance

  • Ranzley
    September 17, 2013

    Can i used here 5v instead of 9v? because my power supply is 5v only.

  • venkatesh
    August 10, 2013

    sir, ihave small confusion in circuit that ,
    in the cicuit at the AUDIO IN can i place microphone and at the AUDIO OUT can i place 8 OHMS loud speaker . then that this circuit works?

  • eng_sarah
    June 30, 2013

    i have mini project and i used simple RF with IR led’s ,, ihave a question regard the 2_ir
    why they are connected in this way ? i mean there is one photo transistor
    the second question how i can simulate this circuit using pspice program
    thank you

  • June 19, 2013

    This is awesome. Very simple to make. Thanks a lot!

  • Avinash
    June 18, 2013

    sir plz …reply……..in my area the give Q2 TR is not ablebal plz tell me which new TR i will use in this place…. MY ID – avinashkumar20rock@gmail.com plz reply

    • November 23, 2013

      use BPW77NA , u got its from good hobi and project making shop where u got all pair parts , i bye it 2 days ago, its price is 50 rs

  • Tuyen
    March 5, 2013

    If i do not have Transistor BC 548. What kind of transistor can i replace it with?
    One more question, what kind of filter are you using in this project?
    How can we compute the cutoff frequency of this filter?

    • manu
      July 7, 2013

      u can use BC546, BC548, BC107, BC148, BC147

  • Happysmile
    January 31, 2013

    I wanna ask what kind of filter are you using in the receiving circuit. And what is its cutoff frequency

  • sara
    November 19, 2012

    the microphone in this circuit isn’t working (although when checked separately its in working state) what should i do?

    • manu
      July 7, 2013

      there is no microfon in this circuit, so u can connect the pre amp out of the audio as the input of this circuit

  • Dude
    November 14, 2012

    This circuit is garbage. Q1 is not biased at all. If the Audio IN signal is AC, Q1 will only turn on for those portions of the signal that exceed 0.7V, resulting in severe distortion.

    Whoever designed this must think that transistors are self-biasing amplifiers, like op-amps: just add power through a load, and your input, and it’s good to go.

    Another problem is that Q1 has no emitter resistor at all. The circuit is aiming for maximum gain. Unfortunately, not only does that mean lots of nonlinearity, but also suboptimal input impedance. Basically the input impedance is just the 1K resistor plus the base-emitter junction’s ESR. That may be too low to be driven by some sources.

  • Goldwin
    July 18, 2012

    Hello Sir Seetharaman, May I ask about C1,What Kind of Capacitor will I used? and the number code of Capacitor?

    • manu
      July 7, 2013

      electrolytic capacitor

  • Devi krishna
    July 13, 2012

    Hai sir any replacement for Q1

  • Seetharaman
    June 24, 2012

    Hi Nilanjan Roy if the transistor is quite cheap, you can use it after painting its body with black paint.

    • Goldwin
      July 18, 2012

      Thanks for the information, seetharaman, it really helps me, making my project!

    • November 23, 2013

      mins what u talk , i did not get u ???

  • June 24, 2012

    npn transistor not found can instated npn transistor 1KL3B

  • oscar
    May 7, 2012

    what type of capacitor is used in the circuit?
    please reply back

  • Freeze
    April 30, 2012

    What is the purpose of using two LEDs?

    For biasing, do we need to connect Q1 base to Vcc? For example, in case where the input signal goes below zero, how will the Q1 be biased if it is not connected to Vcc?

    Many thanks.

  • Seetharaman
    April 25, 2012

    Hi Badri please read about RC filters you will understand.

  • badri
    April 24, 2012

    Use 470PF ceramic disc in parallel with the input and an isolation capacitor 0.22uF ceramic disc between input and Q1 base.

    my question:how do you calculate this value of capacitor? and what is the value of resistance in RC filter?
    Best Regard

  • badri
    April 24, 2012

    i see in oscilloscope after transistor Q1 in side collector, the signal is cutting in up side .why?

  • Seetharaman
    April 23, 2012

    Hi Freeze Use 470PF ceramic disc in parallel with the input and an isolation capacitor 0.22uF ceramic disc between input and Q1 base.

  • freeze
    April 23, 2012

    thanks Seetharaman
    During the application design I found noise.
    I think put the capacitor in audio IN but how much value of capacitor

  • Seetharaman
    April 22, 2012

    Hi Freeze to list afew IR323, QEC112,113, IR-204, CQY37N, IR333C, OP297AB.
    Hi Ali anything between 10 to 20 Deg

  • ali
    April 21, 2012

    can i have more material about this circuits?

  • ali
    April 21, 2012

    sir. may i know the viewing angle of the phototransister?

  • freeze
    April 21, 2012

    i want ask about D1 & D2, what the number model of this component

  • Seetharaman
    April 17, 2012

    Hi Kiran it is from the transmitter. the current through the standard market IR LED is around 10mA, through R1 there will be a drop of 10volts which is not possible hence low current will flow through LEDs and Q1. Each LED requires 1.3 volt at 10mA a drop of 4 volt is required. 4 / 0.01 is 400 ohms reduce R1 to 390 ohms and add a resistance of 22K between collector and base of Q1. add an isolation capacitor of 0.22uF ceramic disc from input to Q1 base. It looks your audio input is of very low impedance you are facing the distortion problem. The above modifications will cater to your requirement.

  • kiran
    April 16, 2012

    hi sir thanks a lot i made it and its working but with some noise.can u tell me how to reduce it?

  • kiran
    April 6, 2012

    hi sir,i want to add a led to indicate that its working.can u please tell me where can i add in the transmitter and receiver.

  • Seetharaman
    April 1, 2012

    Hi Salman the receiver will get damaged (Q4), if the the load resistance connected to output is less than 470 ohms.

  • salman
    March 31, 2012

    Sir, is this circuit is restricted to only 9v pp3 battery only? My circuit damaged when i used an adaptor as power supply! Also how to add a amplifier at output?

  • kiran
    March 23, 2012

    sir can i turn this into wireless communication by connecting a mic at [transmitter] and a pre amp to the output[receiver] then to a speaker.Is this possible???

  • kiran
    March 22, 2012

    thanks sir

  • Seetharaman
    March 22, 2012

    Hi Kiran see the notes it indicates clearly that you can use any NPN photo transistor. There is nothing called most powerful photo transistor, for higher sensitivity use darlington photo transistor with additional external optical lens.

  • kiran
    March 22, 2012

    hi sir,
    can i use any other NPN photo-transistor.please reply
    thank-you

  • kiran
    February 25, 2012

    hi
    which is the most powerful photo-transistor as all the types are available.
    thank-you

  • kiran
    February 20, 2012

    thank-you anish

  • kiran
    February 20, 2012

    sir,
    is there a condition that the Transmitter should point the receiver or from any where it can reach.

    thanks

  • Anish
    February 3, 2012

    Hi kiran,
    Leave the base terminal(do not connect it in the circuit)

  • mcleja
    February 2, 2012

    I just made this and it works!

  • kiran
    January 28, 2012

    dear sir,
    where should I connect the base of the Q2 photo-transistor?

    thanks

  • mcleja
    December 24, 2011

    Thank you.

  • seetharaman
    December 23, 2011

    Hi Meleja you can use these transistor for all the transistors (Q1,2, 3&4)

  • mcleja
    December 22, 2011

    Hi, would these transistors work?

    http://au.element14.com/fairchild-semiconductor/pn3643/bipolar-transistor-npn-30v/dp/1163522

    Im thinking that i will need them because i can only find 100ma 1.5v ir leds.

  • seetharaman
    December 21, 2011

    Hi Meleja yes they are 1.5 volt 20mA IR LEDs(IR emitters)

  • Aniket
    December 21, 2011

    thanx a lot sir !!!!!
    u replyng so fast thats so great of u !!!!

  • mcleja
    December 21, 2011

    Are D1 and D2 1.5 volt IR emitters?

  • Seetharaman
    December 19, 2011

    Hi Aniket any one of the following can be used BPX43, BPW85, L14F1, BP103, BPW17, BPW20, BPW77, BPW78, BPV11,

  • Aniket
    December 17, 2011

    sir they are not giving me any photo transistor if i asked they are asking for the number of transistor so plz tell me number of any npn silicon transistor which is generally available any where !!!!

  • kiran
    December 12, 2011

    dear sir,
    thanks for speedy reply.your advice information always helpful to beginner like me.Sir do you know what technology is used in IR helicopters [small].If you know please reply me.

  • Seetharaman
    December 12, 2011

    Hi Kiran to avoid line of sight problem,use RF transmitter and receivers to control your helicopter (normally the rc is supplied as part of equipment by the toy supplier and not available in the free market).

  • kiran
    December 12, 2011

    dear sir,
    i wanted to apply this idea to make a transmitter and receiver for my micro rc helicopter which i have made.Can you please help, I think we have to slightly change the circuit.Can you please tell where and what to connect.

  • Aniket
    December 9, 2011

    Thanx sir !!!

  • Seetharaman
    December 6, 2011

    Hi Aniket any silicon NPN photo transistor could be used.

  • Aniket
    December 6, 2011

    The above photo transistors are not available plz tell me other phototransistor which i can use

  • virender
    December 5, 2011

    Thanks a lot! Dear seetharaman. Can you please send me more information regarding “home made photo-transistor” by mail me to: “vrndrsngh85@gmail.com” Your reply shall be hightly appreciated.
    With Regards!

  • Aniket
    December 5, 2011

    What audio input shud i use ? ? ?
    should i usee general purpose mic or anythng else ? ? ?

  • Seetharaman
    December 4, 2011

    Hi Virender if you have a old optical mouse from which you use. or you can prepare one by using a bc108 or 2N2221. by filing the edge of top portion of the transistor remove the top disc. clean internals with pure alcohol dry and then fix a small transparent plastic disc in the top hole with suitable adhesive. you photo transistor is ready.

  • virender
    December 4, 2011

    Hi all, can anyone please let me know how to change Q2 in the receiver side. I could not find any NPN phototransistor like PNZ154, PNA1605F, BPW77NA or BPW85 in our area. Any reply shall be highly appreciated.
    Plase mail me to :vrndrsngh85@gmail.com. Thanx in advance.

  • sumya
    December 1, 2011

    nice brooooooooooo.

  • seetharaman
    November 27, 2011

    Hi Rio the additional cost is not going to give any effect on the receiver.

  • Rio
    November 27, 2011

    what happens if i put 2 phototransistors?

  • virender
    November 23, 2011

    Dear sir, can u plz. let me know how to replace Q2 phototransistor with IR LED. I mean I want to use IR LED by replacing phototransistor in IR Audio Link Circuit. It is possible? Any reply shall be highly appreciated. With thx.

  • alex
    November 7, 2011

    how can i get the complete inverter circuit

  • seetharaman
    November 4, 2011

    Hi Rajesh D1 & D2 are IR diodes. You have to take care of anode and cathode. transmitter and receiver should see each other line of sight is important.
    This circuit transmits mono signal only. For stereo encoder and decoders are required. The principle of operation is the communication through modulated IR signal. The audio source modulates the IR LEDs they transmit modulated IR beam. The IR transistor in the receiver receive the signal it is demodulated and amplified by Q3 and Q4. For stereo a simple way will be use two identical circuits for each channel. use polarizing glasses for each channel transmitter and receiver. Use vertical polarization for one channel and horizontal for the other.

  • sujeesh
    November 3, 2011

    Hai,
    is this circuit transmitt mono signal or stereo signal? If it is mono how can i make this stereo. What is the input voltage of audio signal in transmitter? Can you tell me how is this circuit transmitt and receives audio signals? What is the principle of working of this circuit?

  • rajesh
    June 1, 2011

    what a value of d1 &d2 in a ckt.it can work in any direction from trans to rece. i need urgent

  • Mobin
    April 28, 2011

    Hello seetharaman, I want to use this circuits in some different purposes – like Remote ON/OFF LED bright Light circuit . I want to use TV Remote in this purposes . If I pressed one time in any button of TV Remote then LED will glow and again pressed remote button LED will be OFF . I want to make this circuit with photo transistor . Please don’t say to use CD4017 and Relay . Because I cann’t use it . Because I have a LED light which have 20 LED’s and 4V 0.5Ah Battery which casing too small to establishe Relay and IC there .

    Please tell me how can I make such circuit with photo transistor ?

    And about this circuit – It for mono only ! How can I make it for stereo ? I don’t understand why most designer design their audio circuit as mono !! What is the problem with designer to make stereo ?? I really don’t understand !!

    Please reply …. I am waiting for your reply ……

  • Seetharaman
    April 14, 2011

    Hi Mohin the output of this circuit, to be connected to a bistable such that its output will go high with one push and with second push it will go lo.
    To make the above circuit suitable for stereo it will become a dual channel transmission, then you require an encoder to multiplex both the channel signals for sending and a decoder at the receiving end to convert into discrete channels. this will make the circuit complicated as there is no suitable IC available in the market for the same. we will try to develop a discrete circuit in the future.

  • Mohin
    April 13, 2011

    Hello seetharaman, I want to use this circuits in some different purposes – like Remote ON/OFF LED bright Light circuit . I want to use TV Remote in this purposes . If I pressed one time in any button of TV Remote then LED will glow and again pressed remote button LED will be OFF . I want to make this circuit with photo transistor . Please don’t say to use CD4017 and Relay . Because I cann’t use it . Because I have a LED light which have 20 LED’s and 4V 0.5Ah Battery which casing too small to establishe Relay and IC there .

    Please tell me how can I make such circuit with photo transistor ?

    And about this circuit – It for mono only ! How can I make it for stereo ? I don’t understand why most designer design their audio circuit as mono !! What is the problem with designer to make stereo ?? I really don’t understand !!

    Please reply …. I am waiting for your reply ……

  • Seetharaman
    March 27, 2011

    Hi Musthafa Audio input is fed to IR transmitter and the sound is transmitted as modulated IR ray. This ray is sensed by the photo transistor Q2 and converted back to audio signal. the out put can be suitably amplified and listened. This is a cable less audio link.

  • musthafa
    March 27, 2011

    what component used in audio in and audio out

  • ian
    January 22, 2011

    hi
    does this circut work, has it been tried and tested.

    thanks Ian

  • April 19, 2010

    Great site! I am loving it!! Will come back again – taking you feeds also, Thanks.

  • mike day
    August 13, 2009

    Hi i am wondering if anyone has got this circuit to work because when I tried it the two receiver transistor got a bit hot any the circuti did not work

    Mike

  • V. Hari Hara Prasad
    March 29, 2009

    I am very much interested in tracing circuits, though I do not build them. I like to see each and every circuit that I come across. I thank Mr.John for his circuits. Can I give some ideas, as expect any one in your group build them for me? kindly reply.

    regards

    v. Hari Hara Prasad
    v.h.h.prasad@gmail.com
    age 53, Male, India

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