[mythtv-users] Re: Homebrew PVR Multi-Circuit

Gert van der Knokke gertk at xs4all.nl
Tue Jun 22 15:48:06 EDT 2004


Steven White wrote:

> It looks like there's enough interest in this project, so I'm 
> definitely going to proceed with it.  Now, I just need choose the 
> interface(s) for the design....dual serial, single serial, one 
> serial-one parallel, etc. (see my previous questions in this 
> discussion about LIRC).  It's probably a good idea to leave one serial 
> port free for other devices.

If you are going to add a microcontroller then it should be quite easy 
to implement a simple terminal like protocol. If an IR command is 
received convert it to ASCII and send it to the RX data pin of the 
serial port. If data comes out of the TX data pin convert it to  format 
suitable for the LCD display, this should be quite easy. As for turning 
the computer on with IR. Most BIOS-es can do something like 'wake up on 
ring' so when the power on IR command is received just pull the RING 
line of th serial port and the PC should start up.
The protocol for sending and receiving can be made as complex as you wish.
I would opt for some simple command for the display like:

- clear screen
- home cursor
- cursor up, down, left, right

The good old printer codes could be used so you have simple 7 or 8 bit 
characters and control codes. By using Escape codes you can implement 
lots and lots of other functions.

On the receiving side just decode (for example) RC5 and add 32 to the 
keynumber so you have displayable output code (button 0 is ascii 32, 
button 1 is ascii 33 etc etc)

This way you can test your circuit through a simple terminal emulator 
(minicom for example)

Button presses of the onboard buttons can be implemented in a similar way.

I once did some similar circuits for my car mp3 player, one was PIC 
16C84 based (including a alphanumeric 14 segment FT display from a VCR) 
and one was 8051 based with a LCD display.
Both  display units  had only two buttons  but  that was by design, not 
circuit limited :-)
Output was RS232. I can dig up the sources if you like.

Gert



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