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Re: Mobile Sensorium [was Re: Time for Serious GPS Application]

From: Doug Sutherland <>
Date: Sat, 6 Jan 2001 17:55:11 -0800

Matt Carlson wrote:

> I'm going to use my Handspring Visor's IR port instead 
> of the universal remote.

Okay then you will be using completely different parts 
and protocols. The Visor has an IrDA transceiver, which
has both transmit and receive channels, designed to 
carry streams of serial data just like an RS232 port 
but riding on infrared transmissions. The universal IR
remote is much simpler, for one thing the remote is 
only a transmitter and the radio shack IR decoder is 
only a receiver. The universal IR remote sends short 
bursts of unique codes, and the IR decoder simply reads
them and passes them to the microcontroller in a TTL
serial connection at 893 baud. The IrDA device OTOH 
is a complete serial communications port. 

> I have the Visor with me all the time, and I've always 
> wanted to find a way to control my wearable through it

Okay, then you have more work to do than simply attaching 
three wires to the radio shack IR decoder and opening a 
port to receive data. You need to interface an infrared
transceiver. I just checked the manual for my PCM-5822 
and discovered that it has a connector for this, yours 
might too, check the manual. If it has this port, you 
should be able to but a transceiver and plug it in, then
use standard drivers and APIs to interface. If it does
not have the port, you'll have to add a circuit to one
of your serial ports to convert the signals (there are 
schematics on the web for this). Your code will be much 
different than mine. All I do is receive a code and 
send it to the PC. Yours is a serial channel, it 
doesn't send anything unless you tell it to. You'll
have to write a small app on the Visor that sends some 
kind of codes or commands, then write the code for the 
CPU side that recives the codes and takes action based
on which are received. You will be effectively doing 
the same thing that I do for communication between 
microcontrollers along a 9600/8N1 serial line. In fact,
you could follow the same protocol that I just designed
using the ESC CTL-Letter [DeviceID][State] scheme. All 
you would need to do is generate these same codes on 
the Visor, and do what my microcontroller does on the 
wearable (watch for the ESC CTL code and process the 
associated command). Here are a couple of sites for 
info on the IrDA procotol:

http://www.irda.org/
http://www.us-epanorama.net/irda.html

And BTW here is info on remote controls (not IrDA)
http://www.us-epanorama.net/irremote.html

> I have some questions:
> I just went to radio shack and picked up an 276-137B IR 
> detector module. Where did you mount this thing?

This detector cannot talk to your Visor's IR port. All 
this one does is watch for the short burts of codes that 
remote controls for TVs and VCRs send. There are ways to
build your own tranmitters to generate these codes, but 
that doesn't make sense on Visor since it already has 
an IrDA port. Check the specs for your EM-350 and see 
if it has a connector for IrDA transceiver ...

> Where can I find a BX-24 for the best price?  So far 
> I've only seen them listed on the manufactuers web 
> site for $49.. although this isn't at all
> bad, I'm wondering if I can find it for better.

I have some bad news. Last time I checked the price was
up to $59 for individual BX24s. Also you need to buy 
the software. There is a kit for $100 that includes a
proto board, one BX24, serial download cable, and the 
software. More bad news: it only runs on windows. It 
is literally the ONLY peice of windows software I use. 

> This last one I need to do research on myself, but 
> I'll ask anyway. I've never programmed a microcontroler 
> before.  For this spacific one (the BX-24) where do 
> I find a website on how to build a programmer, and 
> what software am I going to need to use?

It seems that all of these basic microcontrollers
(parallax basic stamp, netmedia bx24, and protean logic 
TICkit) don't require hardware programmers. Instead you 
run software on a PC and download to the microcontroller
via serial cable. For other more traditional assembly 
and C based micros you often need a programmer. It may 
be cheaper to use the parallax stamps, but the netmedia
BX24s are much more capable. I don't think I'd even 
try these multiplexing tricks with parallax stamps. 
I also have some protean logic TICkits, they are also 
$59 each and the software is $35 so they are about the 
same price for approximately the same feature set. You 
could of course dive into C/ASM programming of PICs 
or Atmel microcontrollers, but I think that the basic
dialect is a good way to start, and they have quite an
impressive feature set for communications and all kinds
of interfacing.

  -- Doug

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  Grow your own Wearables: http://wearables.los-gatos.net
 What I'd like is to have you call me and my jacket answers
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