We are two engineering students and we want to do a regulation system of temperature with a response time less than 1 second. So, we want to use following devices :
1 or more thermocouples : operational amplifiers will probably be needed with preliminary calibration
A power alimentation (12V - 20A max) controlled as a PWM will be used to heat water with a thermoresistance
A LCD touch screen (between 3.2'' and 7'') to display three indicators (setpoint, real process and thermical power values) and three buttons to modify the setpoint value (up, down and validate)
We want to know which Arduino card is adapted for our needs. Ideally, our budget is less than 120€, 150€ max.
Thank you for your attention and for your future answers,
Yes, we made some researches on it but we prefer an outside advice.
So, we have also seen the Sparkfun 3.2'' touchscreen but it is too small for our application. Indeed, we need a color touchscreen around 4.5'', like this : https://www.sparkfun.com/products/11740. Is this screen compatible with the same card or should we change the card ?
About the price of the screen, forget our budget for the moment and we will adapt our project consequently. It is just to have a first idea about that.
If you're just heating water a DS18B20 (-55C to +125C) would be much less expensive. They guarantee a .5C accuracy but their precision is about ten times greater and once calibrated will match or surpass a thermocouple. The only time you really want to mess with a thermocouple is when you're dealing with +125C temperatures.
With respect to an output display I think you would find it far easier to develop an application on a computer and communicate with the Arduino (via it's USB connection) to control your setpoints or output the current temperature trends / etc. See Arduino Playground - InterfacingWithSoftware.
While the 4D Systems display will certainly interface with the Arduino, you still face the Arduino's limits of memory or program size when developing the interface -- a consideration you don't worry about when developing on a PC or laptop. If you're new to the Arduino game it's not something you want to start tackling right from the start.
In fact, we are working for a start'up. The start'up is setting up a special module with thermocouple type-K and water may be replaced later by another liquid.
I understand and I agree with your point of view but our chief wants a regulation box with all devices I precised at first post. So, I am not sure that he wants to use a computer next, but I will ask him. If he doesn't, we will order a 4D Systems display and do with it .
More, there is an only type on the Arduino store.
In fact, what is the difference between each version ?
I think we must buy the second (or the third because it seems the same version) choice but we are not sure.
Any of those boards would be OK for your project, but the two R3 ones are the latest design. The non-SMD versions (the 2nd and 3rd in your list) have the small advantage that if you damage the atmega328p microcontroller, you can replace it.
Personally, I would choose a Leonardo. It's slightly cheaper than the Uno, has a few more I/O pins, and the serial port isn't taken up by the USB interface.
To interface thermcouples with an Arduino, the usual choice is a MAX31855 chip.
regulation system of temperature with a response time less than 1 second. So, we want to use following devices :
Before worrying about a control system, have you done the thermodynamics.
How much water?
How big a temperature change in the 1 Second?
The energy requirements need to be considered and response time of your temperature sensors, also response time of the heat source.
If your energy supply and sensing gear is not up to scratch, then an arduino will not fix it.
I agree that the arduino can do the controlling you talk about, but with the required response time, there are a lot of other variables to consider.
If it is only a small amount of water say 100ml then it will be interesting to see that you come up with.
Nespresso machine comes to mind.
You might like to look at the reflow oven controller shield, which has everything you want and example programme utilising pid libraries. Output transistor may need some attention though.
Is a touchscreen really necessary , the lcd on the shield was ok for me by add ing a couple of extra buttons on a dev board.
There are 2 onboard laready.
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