i am designing radio transmitter and reciever

[bhuvaneshnick]

parts i have : antenna wire,magnetic wire,toroid core, 23 mhz crysrtal oscillator,some transistors ,resistors,capacitors....

i want to design circuit to simply on and off the led by radio waves.

could u sugest me simple circuit with to do this.. plzz.thank you in adavance

 

[Nigel Goodwin]

As what you're wanting to do is illegal in any civilised country (and probably in the un-civilised ones as well) it's unlikely you will get many suggestions.

Most countries have specific licence free areas you can use, although you need to either use approved and tested modules, or submit your own for testing (along with a big pile of currency).

It's pointless coming up with excuses - it's illegal, end of story - NO excuses.

 

[bhuvaneshnick]

i heard this frequency is legal in india.that why i come up with this

 

[Nigel Goodwin]

i heard this frequency is legal in india.that why i come up with this

It sounds unlikely, and as it can travel thousands of miles it's not just an India problem

Google doesn't find any suggestion that such is the case, and even assuming it was your device would probably require sending away for approval testing.

 

[zcc-China]

I think it have to be lawful if yours is localized ,and you can find out a circuit diagram,it's too easy.

 

[cowboybob]

I think it have to be lawful if yours is localized ,and you can find out a circuit diagram,it's too easy.

My emphasis.

Ah, there's the rub.

Achieving "localized" transmission is extraordinarily difficult with RF. Maybe (and I emphasis maybe) you can accomplish this by very low power (milli-watts) and a very directional antenna. Maybe not.

What is your intended range for this signal to control the LED? Perhaps you might consider an infrared link, like a TV controller (short range, but perfectly legal).

 

[ramuna]

Hi bhuvaneschnick,

Your question is similar to one asked nine years ago in this forum, on Radio Controlled cars:

https://www.electro-tech-online.com/threads/r-c-toy-car-transmitter-circuit.14925/

The opinion of the respondents then (one of whom is also a respondent to your current question) was that it would be far cheaper and safer to buy a ready-made unit (compliant with RF emission regulations) than it would be to try to build one of your own. What was true then is even more true today. A quick Google search produced this result:

https://www.oznium.com/remote-switch

which I presume is legal in ITU Region 1 (USA), although the operating frequency is unfortunately not mentioned. India is in ITU Region 3 and will have different frequency allocations for Low Power devices (although the 4th customer reviewer for the above product, was located in Australia, which is also in ITU Region 3, and appears to have gotten away with using his device).

But since you can disagree with the consensus advice and search out a transmitter circuit and construct it regardless , I would suggest that instead of 23 MHz, you use the nearby frequency of 27.120 MHz. This is bang in the centre of the ISM (Industrial, Scientific & Medical) frequency allocation in the 6 metre band in India (see item IND10 on page 151, here : **broken link removed**

Indeed, the above ISM frequency band is free of licencing requirement, worldwide:
https://en.wikipedia.org/wiki/ISM_band

You can construct an unlicenced transmitter at that frequency provided that its under 5 watts, which should be easily achievable. I would strongly advise you to use a crystal controlled TX design, with the crystal frequency of 27.120 MHz and to use one of the several Remote Control transmitter circuits in the 27 MHz region, which are available online. Such crystals are both widely and cheaply available, eg:
https://uk.farnell.com/txc/7m-27-120meeq-t/quartz-crystal-27-12-mhz-smd/dp/2101321