Trying to select a mini PLC

[rpoet]

i second yosi, arduino is the cheapest.

It's the cheapest, until you consider that it comes "naked" and has no ability to interface with the outside world without building custom circuitry. An Arduino can't directly control a 24v relay, for instance. It can't directly read a thermocouple. It doesn't even come with a power supply. Once you consider all the needed extras and add-ons, it's not nearly so cheap. Plus, you have to factor in the time needed to build the custom interface circuits. And what if it fails? There's no off-the-shelf replacement available.

Hobbyist-grade electronics like the Arduino and PICAXE are much less robust physically, can't mount to DIN rail without a custom-fabbed bracket, and are much more prone to electrical noise (I just chased that particular problem for almost a day, earlier this week) than a product engineered for the demands of a control system. Bottom line... you get what you pay for.


-rpoet

 

[adisharr]

I'm with rpoet,

In any industrial application, there would be no good reason for me to ever use an Arduino for all the reasons listed. I can walk just about anyone through logging into most of the controllers I use and doing some basic troubleshooting. Not so with a board level microcontroller.

In this case though, it might be an option. It really depends on how comfortable the user is with microcontrollers. It could be a fun home project.

 

[chiraldude]

It's the cheapest, until you consider that it comes "naked" and has no ability to interface with the outside world without building custom circuitry.
-rpoet

That is exactly what has kept me from buying Arduino. After I started adding up the nickles and dimes to buy the add-on stuff, I am about 70% of the cost of a mini PLC. Most likely I will then end up buying several components that I end up not using...

 

[Bering C Sparky]

I also automated my home but did the whole shebang. (alarm, lighting, air and heat, motion sensors, irrigation, etc)
I used 3 A.B. Micrologix 1400's.

The A.B. 1100 that was mentioned previous by someone else would be a good choice for your project.

For a really small job Siemens Logo is another you can look at, it may not be very popular with others but it is very inexpensive and I have lots of them in service for small stand alone jobs that dont require remote access and have no problems at all with them. They are bullet proof.
You can get extra analog expansion and also RTD input expansion.
They do have P.I. capability (although I have never used them for that).
They have no online editing or realtime viewing of the program for that mater but they do have a simulation program you can run to test and debug.
http://www.automation.siemens.com/salesmaterial-as/catalog/en/simatic_st70_chap02_english_2013.pdf

 

[Bering C Sparky]

Let me correct my last post before someone else does.
The Logo has no online editing or realtime viewing of the program as you would think of such as with the M.L. 1400 for example.
But you can get it with a small LCD screen onboard where you can see the I/O function in real time and make online adjustments to things like timers and the P.I. function.
Base unit with LCD screen is around $125.
Good luck with you project.

 

[realolman]

I am gonna chime in here in favor of the Micro820 and the CCW software.

At first it drove me nuts, but after I got the hang of it, I gotta say I like it.

It's inexpensive, the software is free, the HMIs are inexpensive and come with built in software.... I've had one working in a factory every day for over a year with no problems ( knock on wood )... it seems to be reliable.. the analog inputs and timers seem to be accurate.

If you have experience programming in Visual Basic, things will go better for you.

I like stuff like the parallax basic stamp and the propeller, but like another poster said if it gets above 3 - 5 volts you gotta start adding stuff... fun if you like it.

and for a wood stove, don't forget about a bimetallic draft control... no power supply needed.

 

[chiraldude]

I am gonna chime in here in favor of the Micro820 and the CCW software.

and for a wood stove, don't forget about a bimetallic draft control... no power supply needed.

I have ordered a Micro820 for the work project and pretty sure I am going with the Click for the stove.

My stove has a bimetallic control built in but it's 25 years old and not designed well to begin with. It's located below the grate on the front so if someone piles the wood closer to the door, it chokes off the airflow too much and if the fire is burning more to the rear of the stove it lets too much air in. My plan is to strap a thermocouple on the flue and have the PID control Flue temp. I also want to tinker with a cold startup setpoint, then a long burn setpoint once it is good and warmed up. I want to be able to load it up with wood, strike a match and forget about it! And yes, I plan to have a thermal cut off switch that shuts everything down if it overheats. Probably a solenoid that holds an input flap open during normal operation.

 

[(8{)} ( .)]

It's the cheapest, until you consider that it comes "naked" and has no ability to interface with the outside world without building custom circuitry.
-rpoet

Just go to ebay and check out the interface boards for next to nothing. You DON'T have to grow your own circuitry. If you're looking for inexpensive AND new you can't beat Arduino.

 

[padees]

I would rather have something a tad more robust.