-----Original Message-----
From: Olin Lathrop [mailto:olin_piclist@EMBEDINC.COM]
Sent: Tuesday, June 18, 2002 8:14 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: HT640 and HT648L encoder/decoder questions


>> I am trying to set up a circuit for an RF control of an LCD.  In setting
up
>> the circuit I discovered that I could only send about a byte a second
over
>> the RF link.  On removing the RF transmitter and RF receiver and
attaching
>> the encoder HT640 straight to the decoder HT648L I discovered the problem
is
>> not the RF devices, but the speed at which data is being encoded and
>> decoded.
>>
>> History:
>>
>> 1) The circuit is driven by a PIC16F877...  I can vary the delay between
>> changes to the pins on the decoder from a single "nop" statement to a
loop
>> of about a second.

>Is there a good reason you're not using the hardware UART built into the
>16F877?  I also don't understand how you "discovered" that the speed was
>about 8 baud when your code produces that timing.  Is there any reason you
>can't set the transmitter and receiver to 300, 1200, or higher baud?  I
>assume these are basic AM transmitter/receivers where the carrier is keyed
>on and off by the incoming signal?  If so, note that this type of system
>need to send a preamble so that the receiver can sense and adjust to the
two
>carrier levels.

I can see how that would be confusing...

The UART is being used to receive RS232 from my PC.

In the end, I would like a circuit that receives a signal from my PC, sends
it out over the RF devices, and drives an LCD.

I put close to a 1 second loop in my program between changes on the pins on
the encoder.  Anything much less than that and the encoder doesn't send the
information to the decoder (not all of it at least.  If I cut the time I
wait in half, then it sends about every other change....)

Again, if I take the RF device out, and directly attach the encoder to the
decoder, it is the same thing....

The RF devices as an FYI are Linx TXM-433-LC-R and Linx RXM-433-LC-S.

By the Way, Thank you for even reading the previous e-mail...  I will
attempt to get the Pic Code later today for any interested party.
Fowler



>*****************************************************************
>Embed Inc, embedded system specialists in Littleton Massachusetts
>(978) 742-9014, http://www.embedinc.com

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