Help me find a 95 MHz transmitter for wireless headphones

• Nov 15, 2005

• #1

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abishek

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most of u will know a wireless headphones has a transmitter and a receiver...
any radio receiver can be used as the reciever only that it needs to tune in to the frequency of the transmitter....

am trying to build a transmitter to transmit at some frequency say 95 mhz....if anyone of u can suggest a good circuit for the trasnmitter with circuit details and an easily available IC......

thanks guys
cheers

 

• Nov 15, 2005

• #2

ramy gad

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Re: wireless headphones

here is the tx
the inductor in the circuit is made from 4 to 5 winding of wire around a pen
it is too easy to made
if you did n't find the transistor in the circuit use any rf npn transistor for example
bf199

 

• Nov 15, 2005

• #3

ramy gad

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Re: wireless headphones

for the the receiver i advice you to use the tda7000 fm receiver chip

 

• Nov 15, 2005

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abishek

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Re: wireless headphones

what xactly is the electret microphone ...how sensitive is it?...
i need something that fits both in an rf socket/mic socket
.....

 

• Nov 15, 2005

• #5

ramy gad

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Re: wireless headphones

simply any condenser mic you may use the one found in your mobile phone ,
the one found in your computer mic , there are two types 2 legs and 3 legs
use the 2 legs if you didn,t find it use the 3 legs use the middle leg with any one of the other two legs
to test this circuit you need an FM Radio

 

• Nov 16, 2005

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abishek

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Re: wireless headphones

doesnt an fm transmitter require a modulation/high frequency carrier??
and how will a condensor help....sound from a tv/audio system needs to go to the transmitter without coming out of the speaker of the system......
if u can xplain the circuit or if anyone can ....will be of great help
thanks in advance
cheers

 

• Nov 16, 2005

• #7

ramy gad

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Re: wireless headphones

the circuit is an oscillator that works at approx.. 100Mhz when we sound signal is injected to the base of the transistor it causes changes in the capacitance of the transistor which in turn change the frequency ==> FM modulator

the sound signal is taken from the condencer mic and amplified then go to the modulator/oscillator

you can remove the mic and get the sound signal from the output of you walkman/tv/(any thing you dream of) and connect it to your circuit
this circuit can be modified to form a telephon bug

good luck

 

• Nov 16, 2005

• #8

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seadolphine2000

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wireless headphones

If you want TX and RX chips, check this site.
https://www.linxtechnologies.com/in...cts&category=rf_modules&subcategory=lc_series

 

• Nov 17, 2005

• #9

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Sceadwian

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wireless headphones

Try https://www.sparkfun.com if you don't want to build the transmitter/receiver yourself and want modules instead. They sell a wide variety of ready to use RF modules.

 

• Nov 17, 2005

• #10

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abishek

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Re: wireless headphones

thanks ramy gad...hope the circuit works...will tell u once i rig it up

also tell me about the telephone bug.....

 

• Nov 21, 2005

• #11

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abishek

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Re: wireless headphones

will any radio receiver work with this circuit
or do i have to have the fm chip that u specified
.1micro henry inductor also works right?(instead of the pen)...less bulky thats y....
thanx

 

• Nov 21, 2005

• #12

ramy gad

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Re: wireless headphones

0.1micro henry inductor is good solution but it is not available in my country so
i have to wind my own inductors

you can use any FM receiver for this circuit
you can use the TDA7000 i tested it and it is too easy for beginners

 

• Nov 22, 2005

• #13

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abishek

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Re: wireless headphones

hey ramy
i rigged up the circuit.....i aint able to catch the signal....

only that at around 98.2 mhz theres noise in the receiver....

what was the xact frequency u recieved it at?

i tried outputting from a pc/mp3player...both dont seen to work

please help me
thanx

 

• Nov 23, 2005

• #14

ramy gad

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Re: wireless headphones

sorry for being late in replying

the frequency of the circuit f =1/(2*pi*√(L*C))
where L = 0.1µH and c is var. adjust c to change the frequency
for testing the circuit i advice you to use a mic first
if you want to use any audio sourse try to make the audio level low(make the volume low) to avoide destortion
you tell me that you receive a tone at a certain frequency are you sure that it is from the tramsmitter ?
turn the power of the transmitter off and chech is there a tone?
if there is a tone then these tone is from the noise of the power supply
try to use batteries they have no noise.(&the cricuit is woking)
i have a circuit called rf prob it test the existance of any rf source it may help you
note : Don't build the circuit on any bread board it will not work
plz reply

 

• Nov 24, 2005

• #15

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abishek

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Re: wireless headphones

hi ramy
have used batteries ony
but have built it on a breadboard only...where else do i have to build it???
and for the C i used a trimmer(variable capacitor)....

plz help
thanks

 

• Dec 4, 2005

• #16

ramy gad

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wireless headphones

sorry for being late in replying
you have to build it on vero board(i have the spelling is write) and soldier your component

don't build it on breadboard as the have many parasits capacitance

Lesson number one in RF don't build any thing on breadboard
plz reply

 

• Nov 28, 2009

• #17

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elockpicker

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Re: wireless headphones

Hi ,I have simulated your FM transmitter is PSPICE and I think there must be a sinusoid on the collector of the modulator transistor ,but I see nothing just 9 volts.
Why is that ?

thank you very much

 

• Nov 29, 2009

• #18

Audioguru

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Re: wireless headphones

elockpicker said:

Hi ,I have simulated your FM transmitter is PSPICE and I think there must be a sinusoid on the collector of the modulator transistor ,but I see nothing just 9 volts.
Why is that ?

Click to expand...

The signal from the mic is only 5mV and the collector of the transistor will amplify it about 64 times if it was biased better.
I calculated that with a new 9v battery the modulator transistor is saturated with a collector voltage of 0.2V. When the battery voltage runs down a little then the modulator transistor will begin to work but become cut-off as the voltage drops more.

It is a horrible circuit that drifts its frequency all over the place. It doesn't have pre-emphasis so it will sound muffled when heard on an FM radio. It is mono, not stereo.