RE: [avr-chat] will an avr be fast enough...

[Derric Tubbs]

Hello, all, complete AVR newb here.

Looking at all this math, are we talking about a
legitimate scenario here?  I mean, can you possibly
fit 16 channels worth of 10bit ADC data down a 38khz
IR pipe???  Are you going to be processing this data
such that it gets broken down significantly?

Also, are you locked into using the MAX1031?  There
are AVRs with 16 channels of 10 bit A2D built in.

Sorry, but my "input" is more for my own learning as
you've raised my curiosity.  I can't offer much help
with my limited knowledge.

Tubbs

--- Robert Dunn <address@hidden> wrote:

> Whilst Im by no means an expert, 
> 
> 720KB/s is 5.76Mbit/s which is a lot of data for a
> little
> microcontroller to handle assuming a 20MHz clock.
> 20MIPS that's under 4
> instructions per bit, or 27 instructions between
> bytes recieved, which
> isnt a lot of time to do much. 
> 
> Assuming a minimum of the 10bits x 16 channels x
> 20kHz that's still
> 3.2Mbit/s (400kB/s) which is alot of data to handle
> at 20MIPS, around 50
> instructions between bytes received. 
> 
> Given that not all instructions are 1 cycle, Id say
> you would be hard
> pressed to handle that with one AVR, but there are
> plenty of other
> people on this list who probably have a much better
> idea than I do.
> 
> Robert Dunn
>  
> Electrical Engineer
>  
> Computer Engineering Ltd
> Room 1, Ground Floor
> Ports of Auckland Building
> Sunderland Street
> Auckland
> New Zealand
>  
> Mobile: +64 21 701317
> Office: +64 9 3794836
> 
> 
> -----Original Message-----
> From: Curtis Maloney [mailto:address@hidden 
> Sent: Friday, 3 June 2005 12:30
> To: Reza Naima
> Cc: address@hidden
> Subject: Re: [avr-chat] will an avr be fast
> enough...
> 
> 
> Reza Naima wrote:
> > So, I'm working on a project where I'll be taking
> data from an MAX1031
> 
> > 16-channel 10-bit SPI based A2D and need to stream
> the data out via an
> 
> > infrared link.  The max SPI clock of the MAX1031
> is 10mhz, and I need 
> > a sampling rate of around 20khz/channel.  Will any
> of the AVRs (I know
> 
> > there's a new small 20mhz one out) be fast enough
> to read the data, 
> > and a checksum byte, and somehow modulate an IR
> LED?  The reciever 
> > will be in close proximity, but going through a
> layer of opaque 
> > material.  It can be configured that minimal
> outside light reaches the
> receiver.
> > 
> 
> FYI - There's also a few Mega series AVRs at 20MHz
> now.
> (I wonder what happened to the 24MHz parts that
> showed up briefly on the
> Atmel 
> web site :)
> 
> Assuming it takes you 3bytes to issue a "read all
> channels" request,
> plus 2bytes 
> per channel, your bandwidth on the SPI is looking
> like:
> 
> 20kHz * ( 16channels * 2B reply + 3B request + 1B
> chk ) = 720KB/s
> 
> So, nothing too scary there, so long as you don't
> need to do masses of 
> processing on the data.
> 
> Depending on the modulation scheme you want for your
> IR, the timers can 
> alleviate a lot of CPU load.  If you're wanting to
> use IRDA, there are
> cheap 
> external chips that can do the modulation for you,
> straight from your
> UART, from 
> people like Microchip, Zilog, and Vishay.
> 
> If you haven't decided on your IR scheme, yet, you
> might want to look at
> a 
> remote control demodulator on the receiver (like a
> Sharp IS1U60) which
> gives a 
> TTL output for the presence/absence of a 38kHz IR
> signal.  Then you can
> OOK 
> modulate your UART output with a timer pin set to
> 38kHz.. I don't
> remember the 
> chip number, but there are some 8ping chips with and
> gates with driver 
> transistors... ideal for this use.
> 
> Of course, my calculations have been wrong before on
> this list.. :P
> 
> --
> Curtis Maloney
> 
> 
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