PLC?



IIRC about all the controller can drive would be an LED, works with SSR's but would need a driver transistor for a 4PDT relay coil. I kinda like TIP120 transistors, something like 3A output capable with a current gain of at least 1000. A ~1K Ohm resistor, TIP120 NPN Darlington transistor and 1N4001 diode should make a nice relay drive... or a lower power SSR could do the job.
IIRC the Basic Stamp outputs can sink or source. I think they can handle a little more current sinking than sourcing, though it's been years since I played with them.
RogerN
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On Mon, 7 Dec 2009 21:00:58 -0600, "Karl Townsend"

Specs are on their website. You'll need drive transistors to operate relays. Someone suggested TIP120, a good suggestion. Holler if you want some help with that.
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Roger, a decent PID algorithm accommodates changes in conditions, and "learns" the lead/lag characteristics of the system. Most of the even most-basic PID controllers (ready made) have that capability.
LLoyd
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On Tue, 08 Dec 2009 09:23:49 -0600, Lloyd E. Sponenburgh wrote:

Yup.
Not unless it's adaptive -- a plain jane PID algorithm isn't adaptive, but can be tuned to be more or less robust to changes in the characteristics of the system.

The ones that I know of aren't adaptive -- they're autotune, which means they'll stimulate the system and come up with a tuning on operator command, but they won't do it all the time.
I don't think things have changed much -- you don't see much hoopla about adaptive control anymore, and the definitive texts that I have read include cautions about when adaptive control won't work (like, blind).
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I agree, except that many commercial PIDs now offer it as a user-selectable option. But you need to understand the difficulties it may impose.
LLoyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

It's been a while since I messed with my Basic Stamp but IIRC they used 8 bit integer math. My Basic Stamp 1 had only about 16 bytes ram, I'm not sure that would do a PID control, maybe. I think the BS2 has about twice that amount of ram. I'm not to great at working with integer math, especially 8 bit.
RogerN
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On Tue, 08 Dec 2009 21:08:33 -0600, RogerN wrote:

Ouch. That's pretty restrictive. You'd need at least 16 bits to do PID in this sort of thing, and mo is better.
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Tim Wescott wrote:

'splain why?
The timing is closer to hours than milliseconds. A real time interrupt (external 555?) for the long delay?
8 bits of temperature is 256 value spread.
The AtoD function can be external hardware, or an external mux if an internal AtoD is there. One bit to select from two sources, two bits for 4.
Motor control is one bit for direction, one for Go. An eight bit count for run time to position the vent.
Too much bloatware in the world today.
What we need are more Assembly Programmers!
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wrote:

Are you volunteering to assist?
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Don Foreman wrote:

Well, maybe...
If I got a "development system" for christmas?
:)
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I talked this project over with my crop consultant today. He said I should apply for a research grant and thinks I'd probably win. In that case, this device needs better EE than I can do. A ways down the road, but would you like to help design phase two?
Karl
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Karl Townsend wrote:

Sure Karl,
You get some grant money for research and development, I'm your geek.
It would be fun. I haven't done a control project in ages.
I have a little CMOS Z80 controller board worked up that should run on about 25 milliamps (not counting off board I/O interfaces, of course).
Personally, I'd go that way and just write in Z80 Assembly, or Tiny C, or as fast as this thing would run maybe even BASIC. Once it's up and running, anybody could then tinker with the software quite easily.
It would be a little overkill, but if I'm writing code, I'd prefer to do it on something I already know.
Fewer surprises.
And, like Roger pointed out, the little controllers are, well, little(!)
Richard
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On Wed, 9 Dec 2009 06:13:30 -0600, "Karl Townsend"

Sure! I have development systems and C compilers for PIC and Atmel AVR. Cavelamb is probably more competent, so include us both!
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On Wed, 09 Dec 2009 10:11:34 -0600, Don Foreman wrote:

So long as you each buy a copy of my book.
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Tim Wescott wrote:

I was afraid you were going to over complicate things, but your articles are pretty clear and readable.
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On Wed, 09 Dec 2009 14:21:09 -0600, cavelamb wrote:

You want things just complicated enough -- in my life I've unwound innumerable vast snarls of kluges that were wound around core functions that were just too simple. When you can double the complexity of the core, make it work _right_, and as a consequence take out five times as many lines of code and/or circuitry from the periphery, then you understand that there is such a thing as _too_ simple.
This is why I'm kind a torn in Karl's case -- he may well be able to get it working with a simple state machine implemented with hysteresis and timing. Unfortunately, the only way to know for sure is to try it out. But fortunately, if he starts with a processor that can absorb the necessary algorithms then he can also start out simple and see how it goes without being married to a too-simple core algorithm from the outset.
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Tim Wescott wrote:

Copy that!
That's what I was referring to re: the small controllers like PICs and Stamps.
And - the reason I still prefer the Z-80 for control work. It has the room and power to expand, a very flexible instruction set (Like 16 bit math, for instance) and decades of practical experience to fall back on.
I really do hate painting myself into a corner.
"Things should be as simple as possible -- and no simpler" Albert Einstein
Richard
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wrote:

Do some of the PIC's have the ability to use external memory(pins used as address and data)? I thought maybe the 17CXXX had that capability, I thought I read it in the specs but never looked at the detail.
Years ago I bought a PIC Servo chipset and built a nice servo control on my solderless breadboard. Once it was tuned correctly it was awesome. The chipset used one PIC to read the encoder and another did the 32 bit math, PID, and trajectory control. It was supposed to be capable of tracking a 500 line (2000 counts in quadrature) at up to 15,000 RPM. And today PICs have a lot more RAM, and program memory.
I have a PIC 16F877 and a PICBASIC PRO compiler, I need to start playing with, maybe make my own robot similar to the BOE BOT my son's getting for Christmas.
RogerN
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On Thu, 10 Dec 2009 05:50:54 -0600, RogerN wrote:

Not many PICs have external memory, but there are some PICs with multiple kilobytes of RAM -- which would be a reason to go beyond a Basic Stamp.
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...

Roger, if my prototype works out, I need to use a less expensive chip than the basic stamp. I assume the compiler you have uses a less expensive chip. What will I have to do to transfer a program? Start all over? Is there a learning curve here? I ask because I have time to learn in the winter, not in the summer.
Karl
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