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karthikeid

Fm transmitter

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The LM2936-5.0 will work down to 5.2V.

The LM7805 will work down to about 6.5V with a low current load.

while considering LDO regulator with 9V battery, i fear the  reason that even if the battery comes to 6V or so, LM2951 would regulate-- is not justified. A 9V battery discharged  till 6V can't deliver any useful load. thus 5.2 as Input from a 9V battery  imagining to serve the circuit  can well be forgotten

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while considering LDO regulator with 9V battery, i fear the  reason that even if the battery comes to 6V or so, LM2951 would regulate-- is not justified. A 9V battery discharged  till 6V can't deliver any useful load. thus 5.2 as Input from a 9V battery  imagining to serve the circuit  can well be forgotten

True a 9V battery with an open circuit voltage of 6V can't produce much current, however when the regulator is connected the open circuit voltage is unimportant. For example, suppose the battery is discharged to the point where its open circuit voltage is 7V but when you connect the transmitter, the voltage drops to 6V; if you were using an LM7805, the voltage to the oscillator will drop below 5V causing it to drift but if you used a LDO regulator, it would stay at 5V.

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Look at the graph of voltage and discharge time for an Energizer 9V alkaline battery at a load of 53mA (my FM transmitter's current).
In about 2.5 hours the voltage drops to 7V where a 78L05 fails to regulate. But it still can power a low dropout regulator for an additional 11.5 hours.

post-1706-14279143972383_thumb.png

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is there any other substitute to overcome this ???


Ideally you need a 5V regulator with a drop-out voltage <1V@50mA will do.

As I said before you could use the LM7805 which has a typical drop-out of 1.5V@50mA but the battery will only last for about 8 hours.

You can buy the LM2931AZ-5 from Futurlec which is based in Thailand and ship globally.
http://www.futurlec.com/Linear/LM2931AZ-5pr.shtml

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Look at the graph of voltage and discharge time for an Energizer 9V alkaline battery at a load of 53mA (my FM transmitter's current).
In about 2.5 hours the voltage drops to 7V where a 78L05 fails to regulate. But it still can power a low dropout regulator for an additional 11.5 hours.

After that point of reaching 7V, I doubt that the said battery would have have capacity to drive the output transistor , through it might still drive the small needs of the LDO output load.

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After that point of reaching 7V' date=' I doubt that the said battery would have have capacity to drive the output transistor , through it might still drive the small needs of the LDO output load.[/quote']
The RF power stage shouldl work at 7V, it just won't be quite so powerful.

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I got a question here: There are commercial FM-transmitters (e.g. from Apple) which send a few meters.
I'd like to build such one and don't want to bother others on the highway by hearing crazy music from my ipod in my oldschool car radio :D
Does somebody know about a schematic to this kinda FM-transmitter?
This transmitter looks nice to me because of the easy way to build inductors :D http://w1.859.telia.com/~u85920178/tx/bug5.htm
but up to 1km range is quite a bit too good for me ;)

Sry for my English

Greets, Br4in

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The modern FM stereo transmitters made for transmitting an MP3 to your car radio have an attenuator at their antenna to reduce their range. You might be able to remove or to bypass the attenuator.

The lousy old BA1404 FM stereo transmitter IC had terrible performance so it was replaced about 10 years ago by the modern ones (BH141x) that work extremely well.

Silicon Chip magazine had a project about The Micromitter that uses the BH1417 IC. It is a kit in Australia. Look at the line of ICs at www.rohm.com .
Here is the Micromitter project:
http://electronics-diy.com/schematics/BH1417_fm_transmitter.htm

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Well, I'm interested in making one myself @Sasi, but to be honest the Micromitter project posted by audioguru is way too big for me...
Is there a way to make an easier transmitter which works fine, or rather is the BA1404 really as bad as you say, audioguru?

Thx for your help!

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Is there a way to make an easier transmitter which works fine, or rather is the BA1404 really as bad as you say, audioguru?

The BA1404 is obsolete. It has not been made for 10 years. Where will you buy one? But some kits still use it.

There are reviews about it on the web. Don Lancaster says it was a terrible transmitter that drifts its frequency so much that a modern digital tuner cannot receive it. Another review say its stereo separation was poor and its 19kHz pilot is a square-wave with many harmonics that causes whistling noises. It has hiss. It has severe distortion. In the 80's (yes, 25 years ago) it was the only FM stereo transmitter IC available.

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A condenser mic needs a 48V supply. Instead, why not use an inexpensive electret mic that has the 48V built-in? The electret mic meeds to be powered through a 10k resistor from a voltage of 3V to 12V that is filtered.

The simple transmitter circuit needs to have an electret mic preamp circuit for a mic to be used.

The simple circuit will sound bad because it is missing pre-emphasis that all FM radio stations have. The de-emphasis in all FM radios will sound like your stereo with its treble tone control turned all the way down.

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Simple circuits never work well because important things are missing.
This one also needs to have a regulated power supply because it is tuned by voltage. Without a regulated voltage the frequency will change as the battery runs down.

With a regulated power supply and a mic preamp with pre-emphasis then the circuit will not be small.

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Why don't you just use the circuit from the datasheet?

Always read the datasheet very carefully before implementing the circuit.

As you've realised, you need a pre-amplifier so why not just look up non-inverting amplifier on Wikipedia and change the resistor values to get the required gain?

To figure out the gain look at the datasheets for the transmitter IC and the electret mic.

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what will be range of transmission...will this be a better transmitter ???

You didn't post a better transmitter.

The MAX2606 has a low supply voltage and a low supply current so its output power is low. Its range might be a few hundred metres to a very sensitive home stereo tuner or car radio with nothing in between or across the street to a cheap clock radio.

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