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

From: Doug Sutherland <>
Date: Sun, 7 Jan 2001 11:25:16 -0800

Matt Carlson wrote:

>> Maybe it's just that it gets back to 4.7v between the fast 
>> signals and your multimeter is too slow and gives you the 
>> integral.

> I thought the same thing.. I might need to start looking at
> ebay again for an oscilloscope

Yeah, the IR decoder is sending logic level voltages of 0-5
volts, but it's doing it really fast, too fast for a mulimeter.
I too need to get an oscope. According to the application notes 
(BasicX) for interfacing the IR detector the baud rate (893)
was determined empirically by connecting an oscilloscope to 
the output pin on the IR detector. Here are the app notes:

http://www.basicx.com/appnotes/Code_Examples/IRserial_BX24.zip
http://www.basicx.com/appnotes/Code_Examples/IR_BX24.zip

BTW Matt I tried attaching the IR decoder to a DB9 connector
and plugged it into my wearable, then wrote a simple routine
to configure the port for 893 baud and listen. It did not 
work. I was hoping this would allow you to test the IR data 
from Visor. But it's the wrong signal (TTL 0-5 volts not 
+/- 10 volt RS232 levels). I have a bunch of MAX232 chips 
and the necessary capacitors here, so I will try the same 
test routing the IR decoder data output through MAX232 to my 
wearable RS232 port and see if it works. It may still not 
work because of the funky baud rate but it would not take 
very long to test. The BX24 microcontroller allows its Com3
serial port to point to any IO pin, and also allows for 
arbitraty baud rates. In my setup the BX24 reads the IR 
decoder at 893 baud, but sends the data to the CPU at 
19200 baud (it uses buffered queues). I still recommend 
putting a microcontroller in between, even if it works on 
the PC serial port, so you can multiplex other devices.

  -- 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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