Subject:
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Re: IR tower question
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 2 Dec 1999 00:43:25 GMT
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Viewed:
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895 times
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Thanks a lot, Reimer, for answering the Ir question. This gives a starting
point for more playing around with the Ir. If only my palm had IR--maybe for
Xmas.
Really clever idea for creating the 38kHz carrier.
Mike
Reimer Mellin <davmel@primenet.com> wrote in message
news:FM2ryE.7KH@lugnet.com...
> IrDA turns 'on' the IR for every 0 bit and holds it upfor ~ 1/2 of the
> period of the transmission frequency.(more on http://www.irda.org)
>
> BTW: For these reasons its better to set the IrDA transmission frequency • to
> 2x38kHz=76kHz and send 0x55 or other similar bitpatterns. This will • generate
> a more acurate IR pattern in terms of timing of the single pulses on the
> receiving side. Your milage may vary though...
>
> On the IR tower side I understand that the (2400 baud) Tx line is basicly
> just 'NAND'ed to the the 38kHz LED driving line.
>
> Sending the bit pattern '10' generates the following IR pattern (ignoring
> start and stop bits):
>
> _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_- 38Khz carrier
> ________________---------------- Bit pattern
> ________________-_-_-_-_-_-_- resulting IR pattern
>
> Reading this via IrDA and @ 38kHz yields (again ignoring the important
> start/stop bits):
> 0x00 0x00 0xff 0xff
>
> Every 'IR tower' bit send will therefore generate 16 (38khz/2400) Ir • peaks,
> which needs to be read via IrDA.
> Lets assume we want to read this via IrDA and are using a 38kHz IrDA
> baudrate:
>
> 16 IR peaks @ 38KhZ have to be recognized and since IrDA requires a Start
> Bit only 14 data bits can actually be read. You then have to configure • your
> IrDA receiver to use:
> 1 Start Bits
> 1 Stop Bits
> 6 Data Bits
> Effectivly you use the first period of the 38kHz carrier as a (required)
> start bit on the IrDA side!
> Therefore you will effectivly receive two 6-bit values for every bit send • by
> the IR Tower
> If you want to use an IrDA freq. of 76 khz the start/stop/data bit
> distribution needs to be adapted...
>
> HOWEVER, Since the Tower sends NOTHING out during the transmission of a 1
> bit, you will have to use some timer device on the IrDA side to determine
> this! Remember IrDA requires Start Bits.
>
> The last point is IMHO really the killer for a Palm solution.
>
> It should be actually easier to send IR data from the Palm to the RCX: Use • a
> 76kHz transmission freq. and send 0x55 0x55 for every 0 Bit and 0xff 0xff
> for every 1 bit. Do not forget to include the start/stop bits for the RCX
> though! Since we use a 76Khz IrDA frequency, the sent out IrDA start Bits
> should be too brief to be recognized by the RCX, whereas the 2bit patterns
> in 0x55 should be recognized as one 38kHz carrier period.
>
> Corrections welcome ..
>
> Cheers
> Reimer Mellin
>
> Mike Kory <kory@advancenet.net> wrote in message
> news:FLEFJ2.6z5@lugnet.com...
> > Robert,
> > I hope an electronics person tells me I'm wrong, because this is where • I'm
> > stuck too. The serial port sets 2400 baud. But my understanding is that • we
> > have to get the Palm to generate a 38kHz signal. That is, pulse the IR • led
> > on/off at 38kHz.
> > So, someone tell me if I have this right: to send a '0' bit the Palm IR
> > needs to pulse on and off at 38kHz for 1/2400 of second.
> > Does the standard for IrDA just turn the IR on and off, or does it have • a
> > carrier frequency too?
> > Mike
> >
> > Robert Eddings <webmake@bellsouth.net> wrote in message
> > news:3833C702.F3E23CF0@bellsouth.net...
> > > I realize that the signal sent is 38 kHz at 2400 baud but isn't that • set
> > > by the serial port?
> > >
> > > Robert Eddings
> >
> >
>
>
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Message is in Reply To:
 | | Re: IR tower question
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| IrDA turns 'on' the IR for every 0 bit and holds it upfor ~ 1/2 of the period of the transmission frequency.(more on (URL) For these reasons its better to set the IrDA transmission frequency to 2x38kHz=76kHz and send 0x55 or other similar (...) (25 years ago, 1-Dec-99, to lugnet.robotics)
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