Need help: Understanding RF remote control

Nov 30, 2005 2 Replies
K

I'm a newbie and am needing some help understanding how remote controls (RF in particular) work.



The device to be controlled: RS-232/TTL controlled mp3 player



Remote control: RF based with number 0-9, pause, mute, volume+ and volume- (very simplistic)



What I'm struggling with are the mechanics of how a keypress gets encoded into a specific data string, tranmitted to the receiver, decoded then sent via TTL to the player. Say I press #9 on the remote which translates to "Start playing MP3 #9." If I know the player expects 02h 09h 0dh to start playing mp3, how do I get button #9 to send this? Is this the function of the encoder/decoder? Does it need to be written into a PIC or a basic stamp? Is this button mapping done on the remote control (transmitter) or receiver? I see rf kits that include a remote control with RF encoder/tranmitter as well as a matched RF receiver/decoder but I'm not sure where the button mapping is done.



Also, I the RF chips I see reference channels - 2, 4, 6 and 8. How is a channel defined and how do I determine how many I need?



Any help would be appreciated, Kevin



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K

Wow, so DTMF as in telephone type sounds? Do most RF remotes work this way, assigning a sound to a keypress which then gets processed accordingly?

If this is the case (I've never looked at these encoders), is the keypress distinguished by a particular set of pin voltages since I am assuming there are limited input pins on the encoder? I'm guessing that a keypress simply closes a circuit which causes certain input pins on the encoder to go high or low based on some mapping ie key 1 = high|low|low|low, key 2 = high|high|low|low, etc..

Otherwise, thatnk you for your input. It has really helped quite a bit.

Kevin

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K

Let's assume you have a 16-key keypad with DTMF (or CTCSS) encoder, an RF module which will transmit that audio to a matching receiver, which can output the tones to a decoder which then passes on the keypress indication to a PIC or other device to generate the control signals for your MP3. Now all you need is for the PIC to accept the single keypress indication and translate to a string of characters which will be read by the MP3 player at RS232.

Depending on how far you want this to go you may be better off getting a universal remote control from a local shop and Googling a PIC-based remote control receiver circuit and then adopting a similar approach to above.

Cheers.

Ken

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