On Tue, 7 Mar 2000, Mark Newland wrote:

>     I have a project that stores both calibration info and data logging
> information on it.  The product will be firmly fixed inside the cab of
> 18 wheelers.  The information will only be accessed once per month.  The
> options are:
>
> 1) Run a 200 foot extention cord out to the unit once per month.  No, I
> can not leave the cord laying out accoss the middle of the parking lot
> for hundreds of trucks to run over it.
>
> 2) RF Link:  Plausible but too expensive when talking about 20-100
> trucks per fleet.
>
> 3) Have the customer buy a laptop and run it out to the truck whenever
> they need to and plug it in.  Customer said "NO!".  They would prefer a
> small handheld unit that will capture the information and can then
> download it to their PC.
>
> 4) Build my own PDA and use whatever IR communication protocals I want.
>
> 5) Buy someone else's PDA (like a Palm Pilot, Handspring, etc.) and just
> program it.
>
> The last option sounds the best but have no idea how to interface to
> it.  What is the spectrum frequency of the IR emittor and detector
> (IrDA)? What is the baud rate on the transmission? When I want to send
> the letter "A" to the PDA, what does the waveform look like?
>
> Unconfirmed info that I have found so far is that it uses 9600 baud and
> it sends a packet of 64 bytes at a time.
>
> Writing the program for the PDA is the easy thing.  What do I do on the
> PIC side to make it compatible??

The palmpilot implements a good portion of the 'IrDA stack'. If you send
the letter 'A', you're in fact sending a whole lot of additional
information. IrDA is a specification that describes the various layers to
a communication protocol that's ultimately based upon infrared receivers
and transmitters. It's not like your TV remote where there's a one-to-one
correspondence between key presses and waveforms that are produced.

The pilot is capable of 115.2 kbaud and the packets can be as large as 512
bytes.

Now as far as pic compatibility, I'm not sure what you mean here. Scenix
has an appnote that implements IrDA (I believe it goes up to to the IrLMP
layer). You may want to take a look there to see how complex this really
is. It probably be easier to store the information on the pilot (that is
in the truck) and then transfer it to a PC either through irda or the
hotsync port. There may even be cheaper ways to store the data (you didn't
say how much data there is). An 'F877 has fair amount of program memory
flash that may be suitable for storing your data - unless you're talking
about kbytes or Mbytes...