Temperature Control
4x5n
Posts: 745
I'm looking to use a Propeller chip for a project that includes among other things temperature control of a water bath. I don't know that I need something as elaborate as PID control but it should be at least P or PI. Has anyone ever done this or know where I can go to find an algorithm?
Comments
http://forums.parallax.com/showthread.php?77656-PID-Control-Intro-with-the-BASIC-Stamp
I started with the Basic Stamp because I saw it on the shelf at a local frys. I've since started puttering around with pbasic and while it's limited it seems rather efficient. I've been looking at the propeller over the last few days and think it may be better suited to what I'm looking to do. What I really like is the ability for it to easily interface with a keyboard and display. I have a development kit on order but haven't gotten it yet. How different is "spin" from pbasic?
You might stick with your Basic Stamp for your controller. Your project doesn't require high speed nor large amounts of memory for variables. It's a good match for the Stamp. You can easily interface a Stamp to a 16-key keypad and a serial 20 x 4 display. If you want to use a TV display, you could use a Propeller Backpack with your Stamp using the display software that comes with it..
I haven't given up on the Basic Stamp. Reading over my last post I may not have been clear but there will be more going on then maintaining temperature. I also need to run a stepper motor for agitation according to a cycle that needs to be "written" (the cycle not the actual underlying program) by the end users. The cycle will consist of say three agitations and then delay 30 secs and repeat for 15 min. All doable by the Basic Stamp. I'm just afraid that I'm going to run out of capacity with the Basic Stamp by the time I get done with feature adds and improvements. Even the temperature needs to be adjustable. I may for now continue along parallel tracks and write code for both and see where it takes me.
If you want, you could add a DS1302 Real Time Clock although you could do the timing with just the Stamp given the long periods involved.
On the other hand, everything could also be done with just a Propeller. How are you measuring the temperature(s)? What kind of display do you want to use? Why a stepper? A servo motor should be able to do the job too with less fuss. What are you agitating? ... a tank? ... a tray?
The first is a rotary processor intended to replace my Jobo CPP (they're not being made anymore and when they come up for sale on ebay go for $2,000+!!) That means spinning a tank 75rpm for 2 revolutions stopping and 2 revolutions the other way. The servos I've seen from parallax don't spin fast enough or have nearly enough torque! A high torque stepper is cheap and can spin at 75rpm without any gearing. The lack of a gear drive means that there's less to go wrong and break.
The second model will rock a tank. The users of this processor will need to be able to adjust the development cycle. The standard Kodak recommended method is to agitate for the first 30sec and then 5 sec every 30 sec. I process film using semi-stand meaning I agitate for the first 30 sec and then three agitations every 3 min. The plan here is also to use a stepper motor with a cam to provide the rocking motion.
Although the market is small and shrinking I do hope to be able sell these processors. That means price is important and aside from the room for growth the propeller over the the Basic Stamp (such as the ability to add a keyboard and display) is the price of the proto board over the Basic Stamp. I know that a PIC is a lot cheaper per unit they have the disadvantage of higher initial costs as well as complexity in getting them on a board and usable. By my back of the envelope calculations I can get the total cost of the controls with motor, heater and power supply for just over $100. At that point a couple of dollars more for the microcontroller isn't significant.
http://youtu.be/imJc_reASCE
Don`t forget to turn captions on!