Making a special controlled heat pad

Hello everyone,

This is my first post on this forum, so first I will shortly introduce myself. My name is Ferdy and I'm working on a new innovation. It's a test method that right now only can be done in a laboratory, and we want to bring it to the field.

So to do this test, the material will be put into a closed container that contains a liquid. This is about 7ml. The combination of this liquid and the material needs to be heated up to 85°C for 45 minutes. After the 45 minutes the real test can be done.

Ok, I know this sounds all a bit vague. But at this stage I can't give you all the details, but I promise you that those details will follow when the project is finished! We want to bring this thing to market this year.

The product
The product will be a base station on which you place a test module. There is a heating element on this station. The liquid and material to be heated will be located exactly on this heating element so that the heat can be transferred to the liquid.

A control panel will be installed at the front of the station. This consists of one or more buttons and an LCD screen. The intention is that the user buys a base station and can reuse it. The battery must therefore be rechargeable or the battery (s) must be replaceable. The moment the user wants to perform the test, he places the test on the station. He turns on the base station and presses start. The timer starts to run and the 7ml liquid is heated to 85 ° C. After 45 minutes, the LCD screen indicates that the heating phase is complete.

What am I doing now?
So I bought the Arduino Starter Kit and a book called "Arduino for Dummy's". Back in my school time I did 2 years of a basic electrical engineering training. So I know the basics about electricity. I'm new to programming, but I believe that everything can be learned if your interests are high and the will to do so is also high.

So I am now working on the first books with projects and getting a feel for the Arduino Uno and programming. I would really appreciate it if you would help me with this project.

First questions

  1. How do you advise me to start this project?
  2. What components would you use to do this?
  3. What (cool) features would you add to this project?

Thank you all in advance for all your input and effort!

Best regards,

Ferdy :slight_smile:

Hello Ferdy.

  • My place to start is with a clear idea of what I want my project to be. First, you would scope out what bare functionality you need. From your description, you need a hot-plate to maintain a temperature of 85°C for 45 minutes on batteries. Then, you would look at adding features and extra functionality (if you really need it).
  • For just the basic heating and timing, you may not need an Arduino at all, though I wouldn't be able to tell you how. That aside, batteries always have the potential to be dangerous if not handled correctly, especially with high current drains like a heater. If you are a beginner (like me), I would not pursue such an ambitious project just yet, because there are lots of things that can go wrong.
    That said, I would use some kind of temperature sensor (maybe a thermocouple?) to monitor the temperature of the plate, and a relay to turn the heater on and off periodically to maintain the temperature. Though, I suppose the parts you use are dependent on your application. If your use case requires high precision, my setup may not be the best.
  • I don't really know what you are testing, so I can't make any suggestions at the moment.
    I hope this was helpful. Good luck and be safe!
    [/list]

You can start with a multimeter with thermal probe
http://www.extech.com/products/MN36
Use the probe to monitor the plate temperature.
Use the meter to measure current flow to heat the plate.
Unless the plate is really small, I don't expect anything except a really high capacity battery (like car 12V lead acid battery) will last for 45 minutes.
When you have more of the basics figured out, then you can start designing your system to be automated.

For example, circuit to monitor temperature, circuit to switch current on/off to the plate for heating, circuit to monitor the battery capacity/voltage level, circuit to monitor the time.
All that can be done with an Arduino and some extra components.
For example, an Analog Devices AD595 to convert the probe to analog for the Arduino to read, simple relay to energize the coil of a relay to connect the heater. Basically an over controller. Let the plate get hot, when its a few degrees below 85C turn it off, let the probe stabilize, turn it off & on as needed to hold the temperature.

My toaster oven (that I use for reflow soldering) for example has 4 heating elements. If I run the temperature up and then turn it off, I see the temperature continue to rise a few degrees then hold before it starts to come down, when I turn it back on, it continues to drop a few few degrees before the temperature comes back up again. I notice that when I am holding for 90 seconds at ~190C, the heat will need to be turned on briefly every 20 seconds, then back off, about 3 times, during that 90 second window.
Your control program will have to account for similar with your plate and environment.

CrossRoads:
You can start with a multimeter with thermal probe
http://www.extech.com/products/MN36
Use the probe to monitor the plate temperature.
Use the meter to measure current flow to heat the plate.
Unless the plate is really small, I don't expect anything except a really high capacity battery (like car 12V lead acid battery) will last for 45 minutes.
When you have more of the basics figured out, then you can start designing your system to be automated.

For example, circuit to monitor temperature, circuit to switch current on/off to the plate for heating, circuit to monitor the battery capacity/voltage level, circuit to monitor the time.
All that can be done with an Arduino and some extra components.
For example, an Analog Devices AD595 to convert the probe to analog for the Arduino to read, simple relay to energize the coil of a relay to connect the heater. Basically an over controller. Let the plate get hot, when its a few degrees below 85C turn it off, let the probe stabilize, turn it off & on as needed to hold the temperature.

My toaster oven (that I use for reflow soldering) for example has 4 heating elements. If I run the temperature up and then turn it off, I see the temperature continue to rise a few degrees then hold before it starts to come down, when I turn it back on, it continues to drop a few few degrees before the temperature comes back up again. I notice that when I am holding for 90 seconds at ~190C, the heat will need to be turned on briefly every 20 seconds, then back off, about 3 times, during that 90 second window.
Your control program will have to account for similar with your plate and environment.

Thank you both for replying!

Good tip about the multimeter with thermal probe, just ordered one!

The plate will be small, right now I'm thinking about 39x12mm, this is 4,5W on 12V. This is a Polyimide heating film. I have to run some tests but when I use a 9,6V 1800 mAh it should be possible to run 3 heating cycles on a full battery.

The heating module only has to heat up 7ml of liquid, so that's a small amount. I was thinking to use something like this: https://www.aliexpress.com/snapshot/0.html?spm=a2g0s.9042647.6.2.71a14c4dT51EEM&orderId=8015462726475046&productId=4000603792416

The circuits you mention are a good starting point. Will hold to that for now. I'll put products behind the circuits, those might change along the project:

  1. Circuit to monitor the temperature, AD595 thermocouple Amplifier;
  2. Circuit to switch current to heating film;
  3. Circuit to monitor the battery capacity (good tip!);
  4. Circuit to monitor the time;

If you have any suggestion on other products/components, please feel free :).

Pippadi:
Hello Ferdy.

  • My place to start is with a clear idea of what I want my project to be. First, you would scope out what bare functionality you need. From your description, you need a hot-plate to maintain a temperature of 85°C for 45 minutes on batteries. Then, you would look at adding features and extra functionality (if you really need it).
  • For just the basic heating and timing, you may not need an Arduino at all, though I wouldn't be able to tell you how. That aside, batteries always have the potential to be dangerous if not handled correctly, especially with high current drains like a heater. If you are a beginner (like me), I would not pursue such an ambitious project just yet, because there are lots of things that can go wrong.
    That said, I would use some kind of temperature sensor (maybe a thermocouple?) to monitor the temperature of the plate, and a relay to turn the heater on and off periodically to maintain the temperature. Though, I suppose the parts you use are dependent on your application. If your use case requires high precision, my setup may not be the best.
  • I don't really know what you are testing, so I can't make any suggestions at the moment.
    I hope this was helpful. Good luck and be safe!
    [/list]

Good tip on scoping this out, I will put some things on paper tomorrow morning. I agree that you don't need a Arduino for the basics, but with this thing I want to do more, as controlling temperature, displaying time, maybe even extend time when the heating process takes longer etc. But those details will be filled in later! First as you said, get the basics right.

This is a test method for paint, the heating process is needed to dissolve the paint in the liquid. We call this the extraction liquid. After this heating process the dissolved paint wil go to a next chamber within the tester. So only a small amount of liquid will be heated, around 7ml.

Thanks and stay safe as well!