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Arduheater - Intelligent heat controller

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jbrazio    45

For the past couple of months I've been working on a project which I named Arduheater.

Arduheater is a full open source intelligent heat strip controller for astronomy usage.

Source code is available at: https://github.com/jbrazio/arduheater

The main design goals were:

Remotely controllable

This was a very important part of the design, most heat controllers, specially the DIY ones, rely on the PWM signal for each channel being manually adjusted by means of a potentiometer. This either requires the user to be near the device tweeking it or to set it to a temperature that may be higher than the one really needed thus completely trashing efficiency. Arduheater uses a serial connection so you can use any USB-Serial-TTL dongle to adjust it's settings either you're 2 or 2000 meters away.

Efficient energy usage

Manual adjusted heater will either require the user to be tweeking it or they will wast more energy than necessary due to the general tendency to use a higher that required setpoint, this is valid for any PWM or bang-bang style controllers. Arduheater uses a temperature sensor (DHT22) to measure basic environmental properties such as temperature and humidity, knowing them both makes the calculation of the dew point[1] possible. Arduheater also has a temperature sensor (NTC) for each heating strip, allowing the micro-controller to have a rough estimation of the temperature the equipment is at; it will be a rough estimation because we are really interested on the lenses surface temperature but we are actually measuring the heat strip temperature, to mitigate this, Arduheater allows the user to set specific offsets per heating strip.

Arduheater uses a PID controller[2] to efficiently manage the energy so only the required amount of energy to maintain a temperature setpoint is delivered to the heating strip. This is possible due the usage of a PWM signal while driving the outputs; the delta between the environmental dew point (plus offset, i.e. setpoint) and the heating strip temperature will make the micro-controller output a PID-calculated PWM signal until this delta reaches zero. In practical terms if a 12V heating strip full on consumes 12W of power (1A) it may be possible for it to use only 1W or even less to keep the equipment above dewpoint and the power usage will be automatically updated during the night as conditions vary, so the system will be always using the least amount of power to keep the dew away.

Builder friendly

Using off-the-shelf components such as the Arduino Nano and easily available parts Arduheater is aimed to be build by anyone with a soldering iron and some patience, no degree in electronics required.

Allow up to four independent heat outputs

Each of the four outputs have independent controls such as offset, min and max output power and of course the three main properties of the PID controller (Kp, Ki and Kd).


Here are some shots of the bench prototype using a power resistor as the heating element and it's serial configuration interface:

01.JPG.414a90c02fc9d14db92505e141435f77.JPG 02.thumb.JPG.323dc7ea71938a0a3154040871a0a4e4.JPG 03.thumb.JPG.447c14058958c62d39a0c070f07e8f00.JPG 04.thumb.JPG.37a742dc8579bc4b504793f7ea4f03e9.JPG


The "field" prototype on it's box:



The heating strips (more build info will be provided further ahead):

06.thumb.JPG.48060ca02e20d14677742a560859758d.JPG 07.thumb.JPG.d4ed9335506d546a5af52ff7dad6c235.JPG


And of course all of this would not be possible without the usage of the force. ;-)



I hope someone may find this project useful.

I'll keep this thread updated as soon as I'm able to release the source code, schematics and build instructions.


[1] Dew point is that dreadful threshold at which water condensation starts to happen on the lenses/equipment.

[2] A proportional–integral–derivative controller (PID controller) is a control loop feedback mechanism (controller) commonly used in industrial control systems.

Edited by jbrazio
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Shelster1973    222

Subbed and watching this with great interest.

Do not haave any form of heaters on my set up at present, only use rather large dew shields, so this may be a great addition

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SteveBz    130

Oh, what a great thread.  Why are there only three posts?

Beautifully written up and beautifully illustrated.  I have an Arduino setup with Guiding, Focus and Exposure control, which I will document (soon) following the standards set out in this post. 

In fact I have bought the Humidity Detector/Thermometer for Arduino and not yet used it.  This thread has inspired me just to get on and do it.

JBrazio thanks very much.



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jbrazio    45

Thank you Steve.

I believe some part is my fault, I haven't finished the schematic so people do not know how to build it (yet).

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jbrazio    45

Finally it's here !

I've updated the project page with the BOM, schematic and prototype board layout.

Visit the project's github page for the latest version of the files.



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jbrazio    45

I've been busy refactoring the current code base, this should come out in the next week or so.
In the meanwhile I've 3D printed and field tested the second version of the box, electronics and heating strips.

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jbrazio    45

Hi @acarrier, the problem is that the ASCOM standard (AFAIK) does not foreseen a standalone heating controller as a device type. I'm currently developing a cross-platform standalone application which will allow you to control all the parameters of the device.

Edited by jbrazio

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skybadger    169

You can use the ascom switch device which takes an output value that's not just 0 or 1.

 Ie any pwm or temp value.


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