[SOLVED] RF or Infrared Technology...simple and cheap is the goal. LED Lightup!

[xecman]

Hello ALL,


The Goal: I'm trying to make some sort of Proximity device that is constantly emitting a signal. Then I want another small object that when within a short range, will light up an LED. The one specific is, it has to be programmable, so an electromagnetic sensor would not work. I was thinking along the lines of RF technology, similar to a garage door opener. If the button was held down on the remote constantly, when it came within range of the RF receiver, an action would take place and the door would open. To translate to my need, If the remote was not a button to press but instead constantly emitting a signal, and the it came in range with the object(Receiver), I want to know the simplest way for there to be a receiver that would see the signal within a couple of feet, and translate that into making an LED either blink or stay solidly lit up.

I was also thinking IR technology. I don't know if you can channel or program that, but I was thinking similar to a TV. If a universal TV remote transmits a signal and then the TV reacts by turning on and lighting up an LED. I know the remote would need to be coded to my TV brand and model, so I was thinking it could be programmed...not 100% sure though.

Sorry for the vagueness, I'm pretty new with learning this stuff and therefore, probably not expressing myself properly. I hope you understand and are able to assist with any information possible.
:roll::roll::roll:

 

[KerimF]

Hi,

Let us assume you have an IR LED compatible with an IR photodiode.
You can drive the IR LED with continuous pulses of a relatively high frequency, in the range 20 KHz to 30 KHz for example.

At the receiver, you can follow the IR photodiode with a band pass filter centred at the TX frequency with a signal detector after it.

If you can get an IR receiver (it may look as a 3-pin TO-126 transistor with an eye) similar to those used in TVs and satellite receivers, you would only need to set the TX frequency at 38 KHz (a typical frequency but should be the same of the IR receiver). The IR receiver though very small, it has, besides the photodiode, an active BPF and the signal detector. Therefore it has 3 pins; Vcc, ground and output. When it receives the IR 38 KHz pulses, the output goes low (typical state). So if you connect an LED with a series resistor between Vcc and its output pin, the LED will be on when it senses the presence of the IR 38 KHz. To reduce the detection sensitivity, one may shift a bit the TX frequency away from the frequency centre (say 38 KHz). The more the difference is, the shorter the detection distance is.

Kerim

 

[xecman]

Thank you so much for such a detailed reply...

Do you think what you explained would be a better option than using RF?

 

[KerimF]

That depends on the viewing angle. IR is simpler but it covers a rather narrower angle in comparison to RF. So it depends on your specific application.

 

[xecman]

Angle is no issue...The object would be lined up at a close distance. My biggest factors are price, and size...The receiver needs to be about the size of a quarter...is that going to be possible at all with either technology? And price point needs to be minimal. You are the man, and I really appreciate the guidance. You definitely seem like you know what your doin!

 

[KerimF]

I guess the IR is better in term of cost and size mainly at the receiver side (if not on both sides).

You may get the small 3-pin IR receiver from a repair shop who might have a defective sat receiver or TV which likely has a small IR receiver (to receive the IR signal from the remote unit). On my side, I buy it (sometimes in quantity) from the local market since it is rather a standard product and even offered as different types.

If you will be able to get one, and you don't succeed to make it work we can always go on together till it works the way you like.

Obviously an IR diode is also needed. It will likely be driven with 555 timer.

Good luck.

Kerim

 

[xecman]

OK great. Thanks for letting me pick your brain. I think I might go down the IR road only because of size and probably less parts needed. I think i'm done hounding you for a while...haha but thank you again, your a great help and resource!