Sprinkler pump controller

PIC or Atmel -- I recommend the Atmel because of the readily available free C development tools and a reasonably inexpensive development kit that handles most of their chips. ($250 or so for the dev kit, or you can find programmers for less than $50 and go right to circuit) I dont know about PIC dev kits but I'm sure they are out there, as are cheap programmers :)

So its really more a question of what languages do you know, and what dev tools are out there for those languages, rather than what chip is best.... even the smallest 8 pin PIC will handle the application you described with I/O to spare (maybe use the left over pins for some status LEDs or a serial interface back to your PC for monitoring and remote control)

A small PLC would probably be simpler, but I don't think you are looking for dimpler. I'd look for an eval board to start with. Almost any small micro. AVR, MSP, ARM just about any would fit the bill.

Data books have become rare, although still nice to have. CDs, are thankfully, even rarer.

Robert

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I've seen systems that measured the moisture level in the soil and ran the pumps accordingly. Popular in Australia I believe.

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What kind of sensor do they use? I might want to use that as another condition to be examined by the micro controller I really don't want to buy a pre-manufactured system, I want to design and build one for educational and potential job related experience.

I guess that I need to go to their web sites to find out their specifications and if I think they would be a good learning tool. What is a popular one that would have the most relevance to many designs?

Do some companies still publish data books? How does one go browsing for parts these days?

I don't know, but a google search on "soil moisture sensors" threw up a bunch of interesting sites. Here are two of them.

which looks as if they rely on measuring conductivity - almost certainly with an AC-excited bridge.

which compares six different sensors - I didn't get much insight out of it, but I didn't read it carefully.

-- Bill Sloman, Nijmegen

The first order of business in a project like this is to FULLY understand the PROCESS you are trying to control. In your case this means you must find out more about agricultural irrigation and the various considerations that go into controlling its application from an agricultural perspective. You don't just jump in with a bunch of minutia about some "manifolded" buckets, pressure sensors, sprinklers, and other odds and ends that you can kluge together to realize your hazy and unsatisfactory idea of what should be good enough. I will give a hint and tell you right now that there is no such thing as an irrigation controller that works based on a "preset" number of days since last rainfall- that strategy is absurd to the point of warranting severe condemnation. You need to know 1) how much did it rain, 2) weather conditions following so as to stress the transpiration rate of the crops, 3) the soil moisture requirements of said crops relative to the integration of the estimated transpiration rate as a function of stage into plant growth development cycle, 4) most favorable time of day and location to apply water, sprinkling is one of the most inefficient means BTW, 5) soil type insofar as water absorption and retention rates,

6)...and host of other parameters related to *agriculture*. It is only *after* you have developed a *thorough* understanding of these requirements and a *thorough* understanding of the various doctrinal control methodology that have proved successful in practice can you even begin to *think* about an instantiation using your little collection of buckets, pressure sensors, and what-nots. Get it?

That depends on the kind of designs you are looking at. Personally I've defaulted to ARM variants as my starting point, they are readily available with a lot of variety and reasonable inexpensive in small quantities. They are also big enough in terms of available memory and processing power to takle quite a range of problems. foe specific jobs other processors may be a better choice to get some desired chara cteristic or peripheral (physical size, high res A/D, low cost, some specific obscure I/O etc...) I don't much like PICs but that's a personal quirk, some swear by them, some at them.

There are a few. Deutsch come to mind as one whose data book is much better than their web site, in their case mainly because of very poor PDFs. Most of the data books I get now seem to be from connector companies. For semiconductors you generally need to beg reps to get Data books, Sometimes they are available, often they are not. The last I got on a micro was a few years ago for a 80C196 variant, the rep had a couple printed out for me.

Browsing for parts is a matter of browsing web sites of the manufacturers and, especially if you are using small quantities, checking a few on-line distributers for stock.

Robert

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Most manufacturers have all their datasheets, selection guides, and app notes available on-line. Searching a distributor's website, such as Digikey or Mouser, can give you a good idea of what parts are actually available.

A google search for IC part number +datasheet will generally locate a datasheet (although you will often get several pay datasheet sites listed before the manufacturer's site)

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What I get is that you don't thoroughly understand that the more important consideration at this time is to learn how to utilize a micro controller and build a system that functions as intended. Your other considerations are of merit but this is for a single residential application, as in my house, not some large scale farming operation. It is a lot more practical than some of these other micro controller projects I have seen posted here by some under-graduate college students that are assigned their by their instructor or professor to build some circuit that counts the revolutions of some shaft or whatnot over a given amount of time. Maybe I'll want to incorporate those other aspects you mentioned above at a later date but for now I just want to controllably water the lawn and learn how to use and program a micro controller.

Just a couple of probes in the ground. Stainless would be best I assume.

"Program" it first at the functional level, before choosing the ucontroller. Two conditions do not "go through" the ucontroller: When the low window bottom sensor is dry, the pump is off regardless of any other conditions; when the high window high sensor is wet, the pump is on regardless of any other conditions. That said, you still might want to have the uc look at them for errors, like the low window low sensor dry but the othere window sensors wet. Once you have laid out all the functions you want you should be in a better position to pick the uc. But it really doesn't matter, as you indicated that you haven't worked with them.

So, what you really want is someone to provide a complete solution, with the uc already chosen and the code written, or someone with experience to tell you which uc to use so that you can then learn how to use that particular uc family. That experienced person will be better able to meet your needs after you have spelled them out. For example, you did not address resetting the timer, error checking the sensors, what to do if the pump is running and it starts raining, whether the timer needs to run during a power failure, what the power on reset state should be and who knows what else.

I'm having a hard time figuring out how this project demonstrates the need for a uc, but I think you could demonstrate the parts cost advantage of one.

I'll show a hardware solution below. The purpose is really background to show that the person reading the resume may think "why in the hell is he showing such a simple use of a uc, when so much more could be done?"

Excluding the timer, a simple hardware solution is a couple of relays. I'll draw the comparator outputs as switches (saves drawing the op amps) All switches made when wet.

Your rain sensor (RS - on when wet) :

/ + ---o o---+---> timer start on break (-) RS | [R] | Gnd --------+

Your low window level top of window (TW) and bottom of window (BW) sensors (on when wet):

/ +---o o---o--- < Low Relay 1 point | BW ^---+ | | | / | + ---+---o o----------+ TW | [Low Relay] | Gnd -------------------+

When the tank is filling, BW closes first as the level rises. When the water reaches the top of the window, TW closes and the relay energizes. It stays energized, if the water level drops, until BW opens.

Your high window level top of window (TW) and bottom of window (BW) sensors (on when wet):

/ +---o o---o--- < High Relay 1 point | BW ^---+ | | | / | + ---+---o o----------+-------< from timer output TW | [High Relay] | Gnd -------------------+

Operates the same as the bottom window sensors. In addition, the relay can be controlled via the timer. That meets your condition of the pump operating when the timer calls for it, regardless of the status of the upper window sensors.

AC ----- < Low Relay 2 Point ^------+ | +--- High Relay 2 Point +--^ | [Pump] | AC -----------+

The point of all that is to show that the uc is not providing a whole bunch of function that mandates its use over hardware. You want the resume to sell a product - you - to the company.

Maybe it would be sufficient for your project to use the uc as the basis for your timer - I don't know. It seems to me a waste of uc power to use it only as a timer in this. Neither the hardware nor software solution can be given until timer reset is defined, but the hardware solution might be a counter like a CD4060 and support components or maybe cascaded ICM7242's. I think it would be a better project if you could do all the "thinking" with a uc - and show enough need for "thinking" that the person reading the resume is impressed. As stated, your project doesn't do that, in my opinion.

Suggested additions: add zones, with individually selectable on times like 4 hours every other day or so many minutes daily or once a week or whatever, sensor logical error checking, maybe an "it's been too dry for too long" alarm to a human operator, etc. The more practical flexibility you put into it, the better.

Ed

Iridium.

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JF

Platinum is usually preferred for conductivity sensors, but soil conductivity is pretty low, so stainless steel would probably be good enough - the layer of chromium oxide (or whatever) that stops stainless steel from rusting has a rather unpredictable range of thicknesses and resistance, but the additional resistance of the oxide layer is usually negligibly small when you are measuring soil conductivity.

-- Bill Sloman, Nijmegen

That depends on the kind of designs you are looking at. Personally I've defaulted to ARM variants as my starting point, they are readily available with a lot of variety and reasonable inexpensive in small quantities. They are also big enough in terms of available memory and processing power to takle quite a range of problems. foe specific jobs other processors may be a better choice to get some desired chara cteristic or peripheral (physical size, high res A/D, low cost, some specific obscure I/O etc...) I don't much like PICs but that's a personal quirk, some swear by them, some at them.

There are a few. Deutsch come to mind as one whose data book is much better than their web site, in their case mainly because of very poor PDFs. Most of the data books I get now seem to be from connector companies. For semiconductors you generally need to beg reps to get Data books, Sometimes they are available, often they are not. The last I got on a micro was a few years ago for a 80C196 variant, the rep had a couple printed out for me.

Browsing for parts is a matter of browsing web sites of the manufacturers and, especially if you are using small quantities, checking a few on-line distributers for stock.

Robert

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Posted via a free Usenet account from http://www.teranews.com

Maybe for a self-centered narcissist it is more important, but, in the real world, the individual engineer/technician is subordinate to the goal of product creation to the point of being a completely insignificant non-entity of the lowest order. Don't plan on impressing anyone with your resume.

Personally, you can cobble up a one-off sprinkler doo-hickey and I'm sure it'd be real nice. But you can perhaps accomplish the same thing by using a Programmable Logic Controller.

Go to AutomationDirect.com and take a look at the DL5 and DL6 models. (There are plenty of others to choose from).

This will get you some good, rock-solid hardware to play with. Lots of options, etc... Inputs/outputs comms, .. (and probably for less $$ than you would otherwise spend in development)

As for the resume, well, these things are usually programmed in "Ladder-Logic". And these days, that's a weird-enough term to catch someone's attention. If they're actually paying attention that is.

I'm afraid have to agree with Fred's comments (above) that the days of impressing anyone with your engineering resume are not what they used to be...

-mpm

Have you used the Keil kits and are their eval boards interchangeable between kits? If I get one starter kit with a certain chip eval board, can I just get another eval board for another chip and it work?

My favorites are DigiKey and Mouser.

I went prodding around Keil's web site and found that the ULink works with a whole bunch of different eval boards and chips. An initial starter kit would be quite useful. Thanks for your pointing me in that direction.