Android Question LED light for communication

[Beja]

The phone's flash light uses LED, which is fast switching because it is semi-conductor. therefore it can be used for communication by adding minimal hardware to it (current driver....etc),
Question is:
1- How fast B4A can switch the LED on and off? (the frequency)

Thanks in advance

edit:
talking about the mobile flash light (not the camera flash)

 

[Erel]

How do you want to flash it? With a notification?

 

[Beja]

Hi Erel,

Have no clue, and don't know which objects are available for the flash.. first time to think about this.
Sorry I didn't do my homework in searching.
if the b4a processing response is fast enough then this will be a great means of communication.. much
faster than BT.

 

[Beja]

Sorry, forgot to mention it is not the notification LED in front of the phone.. it is the flash light in the back that people
use it when the place is dark, just like the traditional flash light.
I want to generate 40kHz frequency then PWM it with my data and send it to an LED receiver.

 

[Erel]

On most devices there is only a single led which is the camera flash led. You can turn it on / off with CameraEx class. However you will not be able to generate a frequency of 40khz. Both the software and the hardware will limit you.

 

[MLDev]

Hi Beja,

Are you trying to send data to a 40KHz IR receiver? If so I'm not positive but I think the flash light won't work. You'll need an infrared LED. Also the theoretical maximum data transfer rate with a carrier of 40KHz is 20KHz. A lot less than BT.

 

[Beja]

Hi MLDev and thanks for stopping by..
Yes, 40k IR receiver, but not the module because it is slow.. I will use the naked IR LED and then take the input to shift registers
and latches before taking them to the MCU. I know there is big job ahead for data verification, but this should not be hard.
BT is RF but the signal is weak and travels very short distance. I have 500m and don't know how to solve the problem.

 

[MLDev]

Yes, BT is short range communications. I thought you meant speed. For a class project, way back when I was in college, I got a network of 5 IBM computers to talk to each other over IR. Each computer just had a IR LED and IR receiver attached to the parallel printer port. They also made pretty good remote controls too.

Just wondering. Why do you need shift registers and latches? Why not just hook the LED directly to one of the MCU pins?

 

[jag]

Some thoughts, ideas...
(These may/may-not be practical, but they might give you some inspiration)
- A laser pointer should go the distance (500m)
- Internet connection
- Plug the phone (through usb) into an external radio data transmitter
(eg: 433MHz), that does the sending
- This site www.futurlec.com has a collection of "Mini" and other boards.
Something there might be useful.

hth,
John

 

[Beja]

@MLDev
Thanks for the input..

Just wondering. Why do you need shift registers and latches? Why not just hook the LED directly to one of the MCU pins?

With this I only have the transistors' propagation delays (not +processing delays) then I tell the MCU take your time. the critical part is the
transmission, not the processing, because I have no control on the incoming data, otherwise I would have used a protocol for the sync.

@jag
Thanks jag for the valuable input.. If I decided to use the 433 (or 490) RF data xceivers then I don't need to use the USB, but bluetooth module with rs485
output connected to the RF radio, so I free the mobile instead of tying it to the radio by USB cable.. what do you think?

 

[jag]

Hello Beja,

> bluetooth module with rs485 output connected to the RF radio

Sounds like you've got it figured out. You'll want to make sure
that whichever rf module you use has the range you need. There's
an interesting discussion about a way to improve range, here:
http://openenergymonitor.org/emon/node/502

Let us know how you make out with your project,
John

 

[Beja]

Sounds like you've got it figured out.

Hi John,
Techwise there is no problem at all.. Also if I am in Europe or other parts of the world then there is no
problem using the 433MHz radios because these countries only need CE certification for RF xmitters, and
most 433, 490... have CE.
But in the USA the story is different.
FCC is required for any range further than a few meters (3 to 4 meters). So I either buy expensive
Motorola radios because they are FCC certified, or try to find another means of communication that's
license free.. that's why I am researching the cell phone flash light because it doesn't need FCC certification.
I hope it is more clear.

 

[Beja]

From the above reply you guess I am working on commercial app. otherwise for personal use
can use the 433 anywhere.

 

[cbal03]

you can buy radios for rc application. these have a 1/4 mi range and are certified. You also get several channels. You can use the older analog frequencies or the newer 2.4G with signal strength feedback. Personally I would go with the analog systems. They are much lower frequencies so passing through solid objects is quite a bit better.