Android Question Is it possible to generate RF frequency?

[Beja]

Hi all,

Is it possible to generate RF frequency and output it through the headphone jack?
android devices use ultra-high frequencies in the range of megahertz.. bluetooth
is all about RF.. so I thought there is a way to also be able to generate your own
frequency, then play with all kids of modulation.

 

[canalrun]

Hello,
I would have to say "very unlikely". But, people are finding new ways to achieve the seemingly impossible all the time.

The hardware you mention generating megahertz is dedicated hardware – dedicated Bluetooth chip, etc.

From what I understand the headphone jack output is connected directly to the audio subsystem. You can generate frequencies, I've done this in the past, but to accomplish this I create a wav file with the desired waveform. The audio sample rate usually goes up to about 44 kHz, sometimes higher. This is definitely not RF.

In the past, I have uploaded some small apps that output waveforms. Search for CanalRun.

There are also quite a few others, including one that outputs a waveform via streaming rather than using a wav file. Sorry I don't have the contributor's name available at the moment.

Barry.

 

[Beja]

Hi Barry and thanks for the valuable input..
Another question about the headphone jack:
What's the maximum current output of the jack? can it drive external IR LED without power supply?
If so then I can use IR instead of RF for the communication.
best,
Beja

p.s.
for some reason couldn't install your app directly from Google play. would you post the apk?

 

[canalrun]

What's the maximum current output of the jack? can it drive external IR LED without power supply?
If so then I can use IR instead of RF for the communication.
best,
Beja

That is a good question. I have never seen specs for the drive capability of a headphone jack on a cell phone, but I would expect it to be pretty small. You may be able to work backwards – that is look at a typical set of headphones and they may list the input requirements. Those would likely fairly closely match the output capabilities of a cell phone.

If I were to take a guess I would say that the headphone jack would not be able to sufficiently drive an IR LED. I remember an IR communications project I did many years ago – the LEDs required a little extra boost in current to make it communicate reliably.

for some reason couldn't install your app directly from Google play. would you post the apk?

Which app are you trying to install? The apps I spoke of earlier are included as Zip file attachments to posts within these forums. My apps on Google Play are different.

Did you have trouble downloading one of the apps from Google Play? Which one?

Barry.

 

[Beja]

Thanks, I was referring to the waveform project that you uploaded here but unfortunately I couldn't locate it.

 

[canalrun]

Thanks, I was referring to the waveform project that you uploaded here but unfortunately I couldn't locate it.

http://www.b4x.com/android/forum/threads/create-write-wave-file.11271/#post-63090

I guess I posted code directly as an example rather than including the project export zip file.

 

[Beja]

Yes you are right.. it is code instead of project..
I am now also thinking of using morse code... theoretically it should be easy if you store the tones, then
concatenate the required sequence at run time (from EdiTtext box or similar variables) and play the wave
files in the same sequence. In your controller you need to convert the morse codes back to their ASCII equivalent.

 

[canalrun]

Yes you are right.. it is code instead of project..
I am now also thinking of using morse code... theoretically it should be easy if you store the tones, then
concatenate the required sequence at run time (from EdiTtext box or similar variables) and play the wave
files in the same sequence. In your controller you need to convert the morse codes back to their ASCII equivalent.

Sounds like an interesting project. I did a communications link project using IR many years ago – around 1996.

IrDA was popular back then. I used a standard IrDA transmitter (IR LED chip) and IrDA receiver (IR receiver chip) along with standard UART transmit/receivers. Basically I replaced the serial cable with an IR link – similar to the way serial Bluetooth now replaces the serial cable with a Bluetooth link.

I wrote software to replace the standard IrDA software stack. I set the baud rate to a fixed value (19200) and did my own simple synchronization and error checking protocol.

In certain situations IR has an advantage over radio-frequency solutions since it has point-to-point security and immunity to electrical noise (but it is affected by strong light sources – like the sun in Mexico ).

If I had the B4A development environment and android devices back then, things would've been much easier.

Barry.

 

[Beja]

Regarding the strong sunlight you can put another LED beside the original to sense the ambient light then reject it.
You will then have something like a dual pipe hunt rifle (the 2 LEDS). Not a very difficult tech challenge I believe.