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Author Topic: swap mic component for headphone input  (Read 2037 times)

trials_modder

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swap mic component for headphone input
« on: May 22, 2006, 01:22:31 AM »

is it possible to swap an electret condenser mic like this one http://www.rpelectronics.com/Default.asp?Main=/English/OnlineCat.asp?Menu=/English/Content/Categories/CatM_70.asp%26Detail=/English/Content/Items/72-160-1.asp with a headphone jack style audio input in some circuit, like this one http://www.canakit.net/Default.asp?Contents=/Include/Template/MenuCat.asp&Main=http://www.canakit.net/Contents/Items/CK105.asp?
i'd rather have this thing broadcast my mp3 player rather than my voice.
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viridius

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Re: swap mic component for headphone input
« Reply #1 on: May 22, 2006, 02:54:41 AM »

You should be able to, there is a part of the circuit that will power and amplify the mic signal and another part that does the transmission.  Do you have a schematic?  Come to think of it, there are probably a few notes on the internet that Google could dig up about modifying a transmitter kit in the way you want.  Sorry if it's not much help, but I don't anticipate being able to communicate effectively for a few weeks; I'll be sunning it up on the Dalmatian coast.
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trials_modder

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Re: swap mic component for headphone input
« Reply #2 on: May 23, 2006, 12:25:51 AM »

ok, swapping the mic for a line in was successful! i can broadcast my mp3 player on the FM now. two things i'd like to do would be to:
a) replace that single wire antenna with one around 85 cm http://www.thesourcecc.com/estore/Product.aspx?language=en-CA&catalog=Online&category=Replacement+Antennas&product=2701402
and b) replace that inductor which is right now a coil of copper and a ferrite core with a better fabricated inductor like the one used here http://24.72.34.35/cgi-bin/twiki/view/Main/TetsuoFM?skin=dragon

so my questions are: will these changes upgrade or increase performance of the transmitter, and if so, where would i be able to get that inductor? (I don't think radio shack carries it)
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viridius

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Re: swap mic component for headphone input
« Reply #3 on: May 23, 2006, 04:15:24 AM »

The length of an antenna in relation to the frequency it is transmitting affects how well it can transmit.  Look for quarter-wave or half-wave equations on the internet.  It should be something like length(m)=237/frequency(MHz) or something like that.
Even the best inductor is just going to be a coil of wire with a permittive core, so upgrading it isn't going to do anything.  If you had a homemade inductor, you might get better stability, but I don't think it would be worth it even then.
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trials_modder

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Re: swap mic component for headphone input
« Reply #4 on: May 23, 2006, 10:20:04 PM »

Well I upgraded the antenna today, which works fine. I haven't replaced the inductor yet, but the reason for doing so is because the ferrite core inside does not fit snugly, so a slight jolt causes the circuit to broadcast on a different frequency. However, I do not know the inductance (measured in Henries or whatever) required for the circuit to broadcast on an appropriate frequency. Will any inductor do?
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trials_modder

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Re: swap mic component for headphone input
« Reply #5 on: May 30, 2006, 02:39:08 PM »

So I emailed CanaKit enquiiring as to what value of a permanent inductor could be used to give me an 88.1 Mhz broadcasting frequency. The person who replied doesn't know. I'm not sure if it is broadcasting correctly ATM, if I use an old fashioned tuning radio, I recieve a loud but slightly noisy frequency, followed by a quieter but clearer frequency just below it. I don't know much about how this thing broadcasts, so could it be due to a lack of voltage perhaps. I've got 1.5 v on it, the max it can take is 6v.
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viridius

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Re: swap mic component for headphone input
« Reply #6 on: May 31, 2006, 03:34:52 AM »

Your best bet is a variable inductor.  Did you wind your own inductor for the circuit?  If so, you can calculate the frequency here and then order a variable inductor in that frequency range.
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trials_modder

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Re: swap mic component for headphone input
« Reply #7 on: May 31, 2006, 09:25:48 PM »

the only problem is I tune the inductor by adjusting how much a ferrite core is within the coil. thus, the relative permeability inside the coil is not constant and I cannot use that link. i read somewhere there is a relation between what capacitor is in parallel with it.
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