basic wireless on/off switch

Hi!

I am given to design a basic wireless on/off switch to work over ~10m to switch a led on and off. And I am not allowed to use any transmitter/receiver modules.

I have read loads of articles about this, but have not found what I am looking for.

1) Is it possible to make a simple transmitter, consisting of an oscillator, rf amplifier and an antenna, which would radiate a single sine wave, which would then be received by a receiver, consisting of an antenna, rf amplifier and a band-pass filter, which would then switch the LED on?

2) What frequency should be used? I think it is better to use an UHF signal, but I can't find any useful information on designing UHF oscillators.

3) And how do you connect the antenna to the circuit? Can it be just a straight wire or a coil, with one end attached to the rf amplifier's output and the other end just "hanging in air" ? Or should one end be grounded always?

There is a lot of information out there, but it doesn't include the very basics.

Thanks!

If you take a cordless FM mike and open it (it is inexpensive), you can see the design and construction. this signal can be received on a fm receiver or you can make a simple one (little involved, not so easy).
The other approach would be to make an oscillator near 500 KHz and a radio am receiver (or o home made ckt) will work as receiver.

But frankly speaking both involve transmission and reception of RF signals in one form or the other.

Will it make sense to use something like a laser diode and if you point it toward the receiving diode, it picks the signal and this can be used to drive a LED.

Other possibility is to use a sound sourced and a sound detector (if needed some selectivity and filtering can be included), this will also allow you to make it.

From the nature of question it appears that conventional Transmitter, Receiver, Microcontroller approach is to be avoided.

UHF is bit hard for a begginer. You can easily construct a oscillator with crystals and cmos ic(you can find lot of them in the net).

So nobody can actually answer the questions, I suppose? That is the problem - everyone is so smart, but when it comes to the basics, nobody is able to give reasonable answers.

vitaxum said:

So nobody can actually answer the questions, I suppose? That is the problem - everyone is so smart, but when it comes to the basics, nobody is able to give reasonable answers.

Click to expand...

Actually your querry is very basic and the real problem is you expect everything in an instant. This is your second post in EDA board and you expect everyone to give you cooked food with spoon feeding. Rather you may let us know what efforts you have put in this regard and what problems have you faced till now so that some may try solving the problems.
Ok for a basic solution here is a cicruit using DTMF En/Decoders with FM transmitter as TX and FM receiver as RX section.
**broken link removed**
Cheers

pranam77 said:

Actually your querry is very basic and the real problem is you expect everything in an instant. This is your second post in EDA board and you expect everyone to give you cooked food with spoon feeding. Rather you may let us know what efforts you have put in this regard and what problems have you faced till now so that some may try solving the problems.
Ok for a basic solution here is a cicruit using DTMF En/Decoders with FM transmitter as TX and FM receiver as RX section.
**broken link removed**
Cheers

Click to expand...

I am not allowed to use any TX/RX modules, as I mentioned in my first post.

Are you allowed to use a micro controller?
If so, look at this page. At the least it will give you some ideas.
SIMPLE FM STEREO MULTIPLEX ENOCDER CIRCUIT

vitaxum said:

So nobody can actually answer the questions, I suppose? That is the problem - everyone is so smart, but when it comes to the basics, nobody is able to give reasonable answers.

Click to expand...

That kind of wisecrack will drive people even farther away. What you're asking for is not as simple as you may think. If you were a professional or an experienced hobbyist and needed help with specific details, then it will be easier for others to help you. But judging from your questions, you will have to be guided step by step through a long process and more experienced members have limited amounts of time and patience for that.

When you made the comment quoted above, you had not even responded to the two members who replied. What they said may not be what you expected, but it would have been good manners to reply and perhaps ask further questions. That way, the discussion will eventually evolve into what you need. Just answering your questions 1 to 3 will not help you much in building a usable RF remote control.

vitaxum said:

Hi!

I am given to design a basic wireless on/off switch to work over ~10m to switch a led on and off. And I am not allowed to use any transmitter/receiver modules.

I have read loads of articles about this, but have not found what I am looking for.

1) Is it possible to make a simple transmitter, consisting of an oscillator, rf amplifier and an antenna, which would radiate a single sine wave, which would then be received by a receiver, consisting of an antenna, rf amplifier and a band-pass filter, which would then switch the LED on?

Click to expand...

Yes, it's possible. For a range of ~10m, you may not even need an RF amplifier at the transmitter. The receiver is usually more complex than the transmitter.

2) What frequency should be used? I think it is better to use an UHF signal, but I can't find any useful information on designing UHF oscillators.

Click to expand...

There's no single frequency that should be used. In theory, any frequency can be used. Some frequencies will be easier to use but not necessarily better. Some will have less interference. Many frequency bands are restricted by law, and there are also restrictions regarding radiated power, frequency stability, etc for any frequency.

3) And how do you connect the antenna to the circuit? Can it be just a straight wire or a coil, with one end attached to the rf amplifier's output and the other end just "hanging in air" ? Or should one end be grounded always?

Click to expand...

There are different kinds of antenna and different ways of feeding them. There is no single method. A wire with one end hanging in the air is one option and is often used for portable transmitters.

There is a lot of information out there, but it doesn't include the very basics.

Click to expand...

That's because technology has progressed too far for many writers to bother with the basics. But there are plenty of literature on the basics of almost any subject. It's just that they often get swamped by all the other hits you get from a search. Consult books too instead of relying solely on the web. The more experienced members here have put in years of hard work to get to where they are now.

You need to first check which frequencies in your area/country you are allowed to transmit on without a license. I believe there are international ISM band frequencies which are license free. Have a look at the table on this website:

ISM band - Wikipedia, the free encyclopedia