Re: TI-H: More AVR Qs
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Re: TI-H: More AVR Qs
Greetings,
This is a consolidation of several replies and my responses to my questions
about AVRs. There are a couple more questions at the bottom.
Thanks for your input everyone!
Nick wrote:
>[Timing precision and accuracy depend] on what you're using as a clock
>source. if you're using a high-grade crystal with some bullet-proof wiring,
>the spec sheets for the part can be extremely accurate (i know that the
>higher-end pics can meausre down to 10 nanoseconds or so..)
For my data logging project I will be needing accuracy and not much
precision. I'd like a drift of less than a second or two over a month. I'll
probably be running it at 4Mhz (or slower, power conservation is more
important than speed). The times I record only need to be precise to about
a second or so.
Would the internal RC clock get me that kind of accuracy (withing a couple
of seconds a month)?
For my timing project I'll be measuring durations of around 25 seconds, with
precision of better than 1 millisecond. I figure I'll run that one at 12
Mhz. Does this sound like a reasonable goal?
Grant wrote:
>You should use the 8515 for digital logging and 8535 for analogue logging.
>They both have 512bytes of SRAM.
512 bytes is way small for my data logging application, which could require
up to 8Kb per sensor channel if left unattented for a month or so.
The analog inputs would be nice (ie, cheaper), but for now I'm sticking with
digital sensors (I happen to have some on hand). I'm thinking the One
Wire(tm) sensors from DalSemi would be nice, but they cost too damn much. I
like them cuz I can put several on the same bus, and they are reasonably
small, so I can stick them at the end of probes and such.
>Use a Mega103L if you need 4k.
Cost and size are important factors here, I'm using the SOIC version of the
AT90S1200, the Mega versions are both too big and too expensive.
>All memory bus AVRs can use an external 64kbyte of SRAM.
What is a memory bus AVR? Does that apply to the 1200?
>EEPROM would die in a few hundred thousand accesses.
PerErik wrote:
>Thats true... better with a SRAM and a Battery.
For my data logging application it would typicaly be cleared every month or
every week at the most, so that won't really be a problem. The timer
project won't need any memory for data storage (results will be sent
directly to a computer via serial port).
Grant wrote:
>Your AT90S1200 has built in EEPROM.
Unfortunately the 64 bytes of EEPROM on the 1200 is next to useless for my
data logging.
From: PerErik Klarenfjord <el8klap@cse.kau.se>
> AT90S1200 do instructions very fast and have 32 registers... but i cant
see any
> "builtin" RAM. :-/
The 1200's don't have any SRAM, the 2313 and 2323 have 128 bytes, the 4414
has 256, the 4424, 8515 and 8535 have 512, the mega chips appear to have 4K.
You can check the spec sheets at Atmel for specifics.
> Do you know the price compared with 16F84 ?
The commercial versions in 20 pin DIP from insight electronics are:
AT90S1200 2.09
AT90S2313 3.09
AT90S2323 2.73
AT90S4414 5.72
AT90S4434 6.71
AT90S8515 7.45
Ok, now a couple more questions.
For now am locked into the AT90S1200 (I already have them).
Is it difficult to communicate with the computer via a serial cable? Since
my AVR will be using 5v, I presume I will need an RS232 level shifter (I'll
be communicating over fairly long distances). Is there AVR code available
somewhere that I can use for RS232 communication?
Is code available to do a PWM output?
Thanks,
DK
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