RF remote control introduction

[ikalogic]

hello,
it have been 2 day i am seeking the net for information about RF remote control..and i want to make sure if i correctly understood everything.

1- there are 2 devices the sender & the reciever which, in order to comunicate with each other have to be at the same frequency.

2- the frequency is set by adjusting the values a coil and a capacitor (in the most basic design).

my questions are:
1- how to give different orders from the same sender to the same device?

2- how the adjust the range of a RF remote system?

those couple questions are just to begin!

thx a lot

 

[Nigel Goodwin]

1- how to give different orders from the same sender to the same device?

You modulate the RF carrier, these days you would use a digital coded signal.

2- how the adjust the range of a RF remote system?

Increase the power of the transmitter, or the sensitivity of the receiver, or provide improved aerial systems at either end (or both ends). Or do all four!.

 

[ikalogic]

well about giving different orders, how to modualte the RF? if i change the frequency of the sender, the receiver wont recognize the signal!??

i want the most basic & old way to do it, i dont want digital stuff, most of time is get usefull in big projects only..

 

[dingo]

well about giving different orders, how to modualte the RF? if i change the frequency of the sender, the receiver wont recognize the signal!??

i want the most basic & old way to do it, i dont want digital stuff, most of time is get usefull in big projects only..

The most basic way would be "digital stuff" if you want the complex hard way then the old way would be the go. With just one encoder/decoder chip you will be replacing 50+ components using just transistors etc.

 

[mozikluv]

rf

hi,

i would like to recommend the following books:

1. RADIO FREQUENCY TRANSISTOR: PRINCIPLES & APPLICATION by DYE
2. RADIO FREQUENCY TRANSMISSION SYSTEMS by WHITAKER
3. SECRETS OF RF CIRCUIT DESIGN by CARR

 

[Nigel Goodwin]

well about giving different orders, how to modualte the RF? if i change the frequency of the sender, the receiver wont recognize the signal!??

You can either use AM (amplitude modulation) or FM (frequency modulation) - in the case of FM you only change the frequency slightly, so it's still within the bandwidth of the receiver. The usual way is to buy ready built radio modules, these are usually licence free and already have data inputs and outputs.

[/quote]
i want the most basic & old way to do it, i dont want digital stuff, most of time is get usefull in big projects only..[/quote]

As already mentioned, doing it any other way (the old way) would be very complicated and expensive. You can buy encoder/decoder chips ready made, Holtek are one of the manufacturers - or you can design your own using PIC's or similar.

 

[ikalogic]

well, to make sure, here is an example:

My sender and receiver are in the range 50 to 80 khz
Say i want to give 3 different orders, sending different frequencies from the transmitter, Then, i would use 3 bandpass filters in the receiver to diferentiate between the 3 orders, which are at 3 different frequencies.

am i on the right path??


thx

 

[Nigel Goodwin]

well, to make sure, here is an example:

My sender and receiver are in the range 50 to 80 khz
Say i want to give 3 different orders, sending different frequencies from the transmitter, Then, i would use 3 bandpass filters in the receiver to diferentiate between the 3 orders, which are at 3 different frequencies.

am i on the right path??

I wouldn't have said so, not in the 21st century!.

There are many ways to transmit remote control information, certainly using individual frequencies does work - and was used, back in the 1970's, but probably not since then. However, it's crude, complicated, and expensive. Using multiple bandpass filters is a particularly complicated way to do it, it would be better to use NE567 PLL tone detectors instead, they were often used for that purpose.

But far better is to use a modern, simple, cheap solution, and will provide better reliability and more channels than individual frequencies.

Here's a link to a Holtek encoder datasheet **broken link removed**, it's a LOT simpler than trying to use antique methods.

Also, you should be aware that the very low frequencies you mentioned for the RF link will have much less bandwidth than a higher frequency one, and are probably un-licenceable in most countries.

In any project you have to make design choices, is there a particular reason why you decided on such low frequencies, and complicated systems?.

 

[ikalogic]

there is only one reason why i chose this compilcated design and such low frequencies: Ignorance!

i am really beginner in the RF domain and have really no idea, so:

do you know a site which explains the use of the decoder/encoder ??
.. as it seems like the only logic solution!!

thx a lot

 

[ikalogic]

hello again!

well, i went to my prefered store and bought lot of electronic equipment, of which is a multiplexer and a demultiplexer along with lot of 555 timers which will be user as counters.

Again i made a lot of researches on the net, and, Again i want to make sure i correctly understant before i begin that project:

To send data, i will use a counter to switch between the 'select input' of the multiplexer which will output the state of all my data inputs, one after the other

To receive data, i will also use a counter to switch between the 'select input' of the demultiplexer which will output the received data to the selected pin at this instant.

If i am right, the counter of the receiver must be started at the same time as the counter of the sender, in other worder, the receiver counter will start when a first signal from the sender is received (i will send a signal from the sender just before begining my stream)

 

[Nigel Goodwin]

This still sounds very complicated and crude - the web page I posted above provides a cheap single chip solution, as would a micro-controller.

Using discrete IC's is going to be very complicated, and use lots of components - for an inferior result.