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It was whipped up in a hurry so it's not real neat, but it works well. It is a temperature controller using a PIC and relay and 16x2 LCD, and a LM335 sensor. It might give you some ideas and there is C source code provided there too.
I used a 12v supply and 5v regulator (for the PIC and display) and the 12v drives the relay.
The project also has a 999 hour count-up timer, good for drying and curing items.
Dude ! This looks really nice. Your "hurry" is great
I'm in a cybercafé, I'll upload some pictures I took for of the tubes I thought about (that was before I took the decision), and show a little tube filled with silicone and a wire in it. I did it to test.
The good thing about this is that I over-estimated how hot a 50°C temperature is. It's really not hot. I put the tube in a boiling water (100°C) and it did just fine, didn't mind at all.
So it's cool, I'd rather over-estimate a problem and find a solution that would work with more clement conditions than be "happy happy everything is fine" and get bitten.
I'll upload them once I set my internet connection again. (Bandwidth here is just so-so).
Mr RB, I'll look more into your page when I'm home and comfortable. Thanks for the thought.
All right, so in case someone stumbles on this thread:
I've written some code for the PIC 16F887 microcontroller which is too big for a project like this (The chip is big, 40 pins, 35 I/O ports if I recall). There is no display for the moment.
I had problems with some portions of the code, but as usual .. Super heroes chimed in and saved the day .. You can go to the thread here
-Port the code to a smaller chip. I'm thinking about the PIC 16F88. This is what I had first in mind. It's a nice 18 pin package which has enough I/O pins for:
-Add the display (dual or triple seven segment display).
Once I get those to work, I'll add stuff to it.
You can go to a page which has a similar project here:
**broken link removed**
This is the code I was going to use. It was a bit broken and I fixed some stuff, and then I didn't find the chip he used. Not being proficient yet to tweak it to a PIC 16F88 "rapidly" (it was for homework at that time), I decided to write my code from scratch eliminating the display for another chip. Now that I've done that, I can tackle porting and adding features, multiplexing, etc in a cleaner way.
I'll clean the comments not to be so messy, and update the thread whenever progress is made. I'm a bit busy right now, learning about oil extraction and well logging techniques, wireline, sensors they use, etc... (an internship with an oil service company) and I'm doing my "homework".
As a suggestion, I would just stay with the 40pin PIC 16F887, it will save you from the hassle of porting the code to the 18pin PIC.
Also, with 40 pins you can drive three 7seg displays directly using 3x7 = 21 pins. That simplifies hardware as you just need 21 resistors and no multiplexing or driver transistors, and of course you won't need any code for multiplexing.
And you will probably still have lots of pins and ADC input left over to add features later if you need to.
Yeah, I thought about that and was a bit reluctant.. You know, I wanted some features from the beginning (ability to chose the temperature, include a pressure sensor to issue that the minimal fluid level isn't attained and shut the heater, that kind of stuff).
I wasn't worried much by the porting itself, but by the size. But it makes sense to leave some room for improvement and stick with the 887.
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This is sweet. 
