Multiple Input Temperature Controllers

[berto]

Hi all.

Im looking at starting a project whereby i build a glycol chiller from an old air con unit. Pretty simple from what i can see on Overclockers Australia. (You will have to go to the forum section).

Then making a stainless coil for each of my fermenters. Again not an overly arduos task hopefully.

But im stuffed if i can find a reasonably priced temperature controller which will control 4 or so relays, based on a similar number of inputs.

Have thought about going down the path of a system running a DAQ card, but dont want a PC running 24/7 just for that. Trying to cut power usage ATM.

If anyone has any ideas, more than happy to hear them.

Cheers, Rob

 

[Trev]

Here's one way.

Have a look at Ozitronics Kit. It can function as a standalone simple controller. You set the trip point by plugging it into a parallel I/F and use the supplied code. After setting the trip point you can disconnect from the PC.

This unit has a a 16x2 LCD which makes it expensive but I'm thinking if you just buy one and build it up, then just make another 3 on breadboard but without the LCD, you can easily programme them/clone etc.

Mount the DS1820's where you want to measure

Maybe have the connector for the LCD etc.

How you interface to the No/NC contacts is up to you.

Or get a PIC and frig with it for ages

Trev

 

[vlbaby]

I built myself a dual channel unit similar to what trev describes using a PIC controller. It wouldnt be too difficult to turn it into a 4 channel if you can program a PIC and are into that sort of stuff.





cheers

vl

 

[berto]

Definately into that kina stuff

FInished elce eng. degree, currently doing power stuff, but wouldnt mind a little electronice experience on the side. If you have any info please send.

 

[vlbaby]

Definately into that kina stuff

FInished elce eng. degree, currently doing power stuff, but wouldnt mind a little electronice experience on the side. If you have any info please send.

[post="101146"][/post]​

no worries. I'll scan the drawings i have and pm them to you.

vl.

 

[agro]

I have seen some pic based projects using the Temperature IButtons and the 1-wire network from dallas semi and a PIX m icro. I'll see if I can find it and post a link.

Agro.

 

[ArnieW]

Hi Berto,

I've got details of a picaxe (pic based micro) temp contoller on my website that is close to what you want. It has full details including component list, circuit board layout etc. for a programmable temp controller.

It only has one channel, but you can use the circuit to upscale it to a larger picaxe with more channels. I have in mind to do something similar for my glycol setup, but that will be a project for a rainy day.

Anyway, I hope there is enough there to get you started.

Programmable Fridge Controller

cheers, Arnie

 

[berto]

Cheers for all the replies guys. I've now just got to decide on what direction i want to go with it, sit down, work out a parts list and buy it all. Like the look of the second one by being able to log in through web browser etc. I can easily get a few cat5 cables run out to the shed to get it on the network. Wouldnt mind getting a memory storage of some sort in there so i can record temperature of fermentation for each brew.


Now gotta call the guy up the road and see if he has any old air-con units which i can salvage as a water chiller and get some stainless pipe to coil. Not sure what that will cost though.

Cheers, Rob

 

[berto]

OK, i think im going to bite the bullet and buy a picaxe. Ive programmed in assembly language at uni, and actually found that reasonably intuitive, and from the guides ive read, the basic program is far more user friendly due to making loops due to time, not clock settings, whereby we had to count clock cycles and, well... if you follow what im saying here, you will know what a PITA it is.

First however i have a few questions.

1) How hard is the LCD to program? The instructions seem pretty easy, is it as simple as it looks?

2) Can anyone think of a way i could comfortably show all temps on the screen? for up to maybe 5 or 6 sensors if the time ever came i was that involved.

3) How long are the cables on the temperature sensors? Are you able to use different sensors which are a metal bulb type build? I realise this would probably remove the cheapness of the sensor.

4) Etching a PCB layout. How hard is it? Do i need many components other than the resistors, diodes etc for the programming and reset buttong?

5) I still haven't read the other code yet, but as for changing temperature settings, this is done by the buttons on the screen i assume? Is this done using interrupts? Are these interrupts hard to program? I had to write interrupts for programming in C. I hated it. think i did them in assembly language too, and didnt like them there either.

6) Costs. I think im looking at $25 for the chip, $50 for the LCD, about $6 ea for the sensors from memory, so theres $100 straight away. I will also need relays, pcb, probably a breadboard for testing before building a final model and other bits and pieces. Can someone give me an insight into anything i may have missed here.

7) Power supply. Am i able to use a 240VAC/5VDC transformer. I see no reason i cant. May even make it a 6V tranny and set up a voltage divider so i can power teh LCD off it as well, but drop the volts into the picaxe. Although a diode in series with it should also give me the voltage drop i need.

8) If i get all this working, i think i may bust out and get the memory chip that comes with it as well, and work out how much data i can store. If i can get a weeks worth of temperatures at 5 min intervals, i would be wrapped.

9) Anythign else anyone can think of?

Cheers, Rob

 

[ArnieW]

Hi Berto,

picaxes are dead easy to use and much cheaper than other micros.

1. The serial LCD is a breeze to use.
2. You can easily show 4 temps on a single screen, you could always alternate (say every second) if you want to show more. I think you can even use LCD commands to scroll info if you wish.
3. You can put whatever length cable you like on the temp sensors (I'm guessing there is a practical limit). The DS18B20s come in a transistor-type package, you add the cable. You can use other temp sensors, but it then is a matter of how the micro will read the info. The beauty of the DS18B20s is that a simple READTEMP command gives a digital temperature reading. If you were using a thermistor, you would need to use an analog to digital input, and cross calibrate the reading with a chart of temperatures, or else use some kind of formula to give a temp readout.
4. Etching a PCB is actually quite easy. You need artwork, a board, and some chemicals. Ask in Jaycar or DSE, or do a google search.
5. Have a look at the link I provided a few posts ago. It will show you code to do just what you want. I can't remember if it is using an interrupt or simply a loop, but both ways are easy.
6. About right. I'd recommend a solderless breadboard for experimenting.
7. Any micro can be sensitive to powersupply noise. The picaxes run for weeks off a few AA batteries, so you could go that way. Otherwise make sure your plug-pack is well filtered. The max voltage on a picaxe is 5.5V and they are sensitive to over-voltage, so if you go with 6V, use a diode or something similar to drop the V.

have fun,

Arnie

 

[berto]

Swore black and blue when i was at uni iwould never touch another another electronics circuit cause they are simply a PITA. Hence i em now working for a power utility working on 11 and 33kv gear. Far easier to understand and work with.

But i think i will take the plunge here now. ok, Ive looked on ebay for larger LCD's, and there are 4 line models on there, and that would be an ideal size i think. Would it require more work to get one of these working?

 

[berto]

Arnie, just a had quick read through the code just then. You ripped it from elsewhere by the looks. Do you find it runs well? Does it seem laggy when performing keystrokes? Seems like it has to cycle through the whoel code to get back to where it will look at your temperature adjustment code in there. I may be wrong though.

This is whay i want to put interrupts in there. Whilst they are a pain to program, they make the code much neater, and far more efficient.

 

[ArnieW]

Hi Berto,

the only code I've borrowed is the temperature maths bit which from memory is the work of Peter Anderson. Having said that, the rest is dead easy.

It could be done more efficiently, but the slowness is really only in the delays I've programmed in. Interrupts would work and they are not hard to use on a picaxe, but you can only use one input at any time with an interrupt. This means that if you wanted to interrupt on both up and down buttons (two inputs), you will need to diode them together onto an interrupt line so that either will trigger it. That is the main reason I haven't done it, and to be honest I dont' think its needed. But when you get to that point you can experiment to your heart's content. There are some good resources around, and a google search on Hippy and Picaxe will get you some good info on using interrupts.

Let me know if you can't find it and I'll look up the url.

Regarding 4 line LCDs, the basic serial interface kits that you plug in work with either 2 line or 4 line. So no extra work, except for the formatting commands in code.

cheers, Arnie