From: Spehro Pefhany
Subject: Re: PIC/Microcontroller recommendation?
X-Newsreader: Forte Agent 1.92/32.572
Date: Mon, 16 Dec 2002 21:11:02 GMT
NNTP-Posting-Date: Mon, 16 Dec 2002 16:11:02 EST
On Mon, 16 Dec 2002 17:18:54 GMT, the renowned Jonathan Kirwan
>I see three digital inputs:
> "extend" momentary pushbutton
> "retract" momentary pushbutton
> "stop" momentary pushbutton
>and three analog inputs:
> "extend limit" potentiometer
> "retract limit" potentiometer
> "arm position" potentiometer
>I assume the four outputs are for the motor control?
Yes, what's the deal? Are there two motors? If so, are they
run exactly at the same time? Why are there not just two
outputs- extend and retract?
For only 100 units, I'd suggest something like the PIC16F87x
series. There are cheaper parts, but that one is reasonable
($2.74 in 100 qty for the 870), supports the ICD (since much of
your cost will be development) and has an 10 bit ADC, which
will give you resolution of better than 1 part in 700. With
28 pins and 2K x 14 words of code memory you shouldn't be
worrying about running out of capacity.
>Whatever you pick, you should make sure that the ports support
>weak pullups, which is probably adequate for your momentary
>buttons, without the need for an external pullup or pulldown.
If you try this, better have some filtering on those inputs,
with only 50-400uA, long leads to the switches and those 1A
inductive motors being switched by relays...
I'd also mention that the MSP430 is limited to 3.6V Vdd and
(IIRC, could be wrong) is not offered in DIP package, only
SMT packages, which may or may not be an issue.
BTW, almost anything you could come up with would be overkill
for this application.
Another possibility would be to use the 18-pin PIC16F628, which
has no ADC, but it does have two analog comparators, which is all
you really need if you think about it. It costs $1.92 in 100's,
but no ICD (ISP, though, so you can do crash and burn
development if you like)
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