Arduino Dew-Heater project

[buikimaging]

Hello all,

As the title suggests, I am making some plans of building an Arduino powered dew heater.
Lately the dew on my telescope has stopped me in my tracks halfway through the night so its time to build some dew heaters.
I want the buildup to be very simplistic in design with as little wires and as basic as possible.

So far I have the basic supplies and ideas for it.
In the sketch below is a very simplistic view of what i have in mind.
I am looking at making 4 dew heaters, 1 for either the 250PDS or the ES triplet, 1 for the guide-scope, 2 as Spare or eyepiece heater.
They are connected to the control box via a cinch connector, inside the control box we have 4 TIP transistors to switch the dew heaters on/off.
These TIP120 transistors are cooled by some air vents in the box and controlled by the Arduino.
The temperature sensors will be 1-wire devices which will be able to measure the heat of the dew band. To make sure it does not overheat.
An external DHT22 will measure the outside temperature and calculate the Dew-point with the temperature and humidity.
With this dew point and the temperature on the temperature probes we can calculate when to turn on the dew heaters.
The dew heaters will be controlled via PWM. They will be made of NiChrome wire for the 250PDS and resistors on the smaller triplet and guide-scope.
To prevent the Dew-Heaters from short-circuit or over-heating we also plan to place a fuse between the TIP120 and the Dew-Heaters themselves. This fuse will be of around 3.75A. (can be changed at a later point)
I added a simple scheme to show what I mean.

For the sharp people, in one of the pictures is a Arduino Uno, we chose to use this as it is bigger and a base for future Arduino projects.

We will keep everyone here updated as the project develops and gets more automated!

Clear Skies!
Buikimaging

[Fish]

You want a simple build, this looks a bit over kill.

When all you need is 4 of these 

http://www.ebay.co.uk/itm/DC-12V-8A-LED-Light-Strip-Dimmer-Adjustable-Brightness-Controller-GU-/371457308567?hash=item567c94b797:g:1yAAAOSwNNxWE16F

Remove pot and circuit board  and install in a box with four sockets.

 

[hughgilhespie]

Hi Buikimaging,

I built the Arduino dew controller designed by Robert Brown. Details below. It is a good design, based on a Nano with a nice Windows interface. Basically, you get a fully automated dew controller with two separate channels.

https://sourceforge.net/projects/arduinonanodewcontrollerpro/files/latest/

 

Regards, Hugh

[buikimaging]

32 minutes ago, hughgilhespie said:

Hi Buikimaging,

I built the Arduino dew controller designed by Robert Brown. Details below. It is a good design, based on a Nano with a nice Windows interface. Basically, you get a fully automated dew controller with two separate channels.

https://sourceforge.net/projects/arduinonanodewcontrollerpro/files/latest/

 

Regards, Hugh

We use exactly the same design however we have our own little touches to make it a bit more interesting. It is a great design he made and we used a lot of our inspiration from him and adapted it to our own needs! 

Thanks for the heads-up 

[brown_rb]

The DewControllerPro was recently updated to v3, which has a PCB as well as now 3 channels each with temperature probe. The third channel can mimic ch1, ch2, be set to manual or use the ch3 temperature probe.

 

[buikimaging]

Progress so far:

We have got the case for the entire dew controller and arduino and recieved our arduino nano. Meanwhile we have got 4 of the temperature sensors read through 1 pin.
This is when we noticed how 3 of the sensors read the temperature within 4 decimals and one only read within 2 decimals.
This could be controlled by programming the internal EEPROM. (those sensors even have a chip in them with memory and all ).
Now the 4 sensors are being read through the Arduino serial monitor. We have soldered the PCB board where there is a voltage regulator from 12-13 to 9V.
The battery we will be using will put out 13.5V at max when fully charged which is too high for the Arduino to handle hence the regulator.
Its doing a great job at holding the voltage at 9 Volts without a hitch.
We built in some of the connectors and 2.5mm jack plugs for the temperature sensors and added the 3.5mm cinch plugs for the heaters themselves.
Progress is steady and everything is working great so far!
The last picture I added is of the big clutter of wires leading to the Arduino Uno showing all the temperature sensors having just 1 input port on the Uno. (The yellow wire in the top of the Uno)
We can acces all these probes through this one port and takes away a lot of excess wires.
The fuse will have the plus wire from the battery attached so in case any of the components short circuits or takes too much current the fuse will blow protecting as much as possible.

The programming and building continues and I'll keep you informed along the way!

[rweust]

Do we need dew heaters in the Netherlands, apparently we do. Looks a lot like my design, the difference is I used a PIC 16F1847 microcontroller. Your humidity sensor is an absolute plus to calculate the dew point. An Arduino is more powerful, has more software libraries to choose from and can maybe even be combined with a USB or remote control. The PIC I use is cheaper and works fine on four hardware PWM channels with the DS1820, DS18S20 and even 12-bit DS18B20 one-wire temperature sensors. It is also equipped with a LDC display and an extra cooling down cycle for the fan, but I’m out of program space now, so no more further features than this. This last point is where the Arduino will win.

 

For the sceptics who never used a PID temperature control and find it an overkill, I advise to read my topic and see what my 4-Channel PID dew heater can achieve on an open system like a Newton (in combination with a low emission foil around the tube). The temperatures on all essential parts at fast dropping temperatures to almost freezing within a 0.5 C window together with the surrounding air temperature. No dew anywhere and no overheated parts neither. This accurate temperature following of the surrounding air, with very stable and constant power output on your heated optics can only be achieved by a PID controlled heating. I used the PID controlled heating only on my secondary mirror in this test and still have 3 channels left to heat accessories with a load temperature sensor or without, as I choose.

 

It is wonderful to have a temperature control which can be set up and hasn’t have to looked after during the night. No worries for dew and no worries about heating some elements to much and causing tube currents neither. No power controller (this is what a PWM LED dimmer is, nothing more) nor switching thermostat, even with a differential control, can get near to the PID controller on this point. Love your design.

Robert.

[buikimaging]

Blew up the voltage regulator due to reverse voltage from the capacitors. Because there was no load on the output the output capacitor was charged with 12 volt. When switched off this came on the output of the regulator and it began to smell .

So got rid of the capacitors and the regulator and put 2 diodes in series to keep the power of the arduino a little bit below the max voltage of the posible 13 volt of the lead acid battery.

Built the first heater for the guider scope out of 330 ohm resitors. And tested the whole thing on the arduino uno and does work like a charm.

Next thing is to make the second heater for the es80 also with resistors. All probes and outputs work if they are connected. And skipped when not connected. The sketch is built to give priority to regulating the temperature of the scopes.  Second priority is showing temperature and humudity and ambient temperature.

When the weather clears up this week we will begin testing the whole set-up for having the right settings for turning on and off the heaters. And maybe a little fine tuning. If all that is done its time to close the case in the hope all Dew problems are gone with this fire and forget dewheater controller. Just put in the heaters and probes you need and startup the controller. More to come! 

 

[buikimaging]

UP and Running.

After finishing al the electronics inside the box and loading the software to the arduino nano.
The test if  the heaters would run at our satisfaction was done in the garden at a foggy evening with no chance of stargazing what so ever but with a big cance of fogging up the guider scope.
Pluged everything in and powered up the arduino.
After 4 hours of testing there was still no dew on the lens of the guiderscope so the test was a great succes.

It kept the scope at a reasonal temp of 8 degrees above dew point.
Fixed the second heater and found a nice place for the controller.
Connected it with felcro between the scopes on the side by side bar.
On that way when the mount is moving only the powercable is moving and not controle wires and probe wires.

Yesterday we had some clear skies after a long periode and went to our favorite dark spot to try to shoot some images.
And at the same time testing the finished dew heaters in freezing conditions.
Noticed that the backlight of the LCD should be dimmed a littlebit further or look for a red or orange one in the future.
But in absent of the red LCD we went for the blue one.
It workt like a charm!! kept both scopes at a steady 7,5 degrees Celsius in -1 degrees Celsius.
Took some nice pictures of Catalina and some open clusters for fun.
Car windows froze up with a thin layer of ice but no pain on the lenses of the scope.
Run the whole night on a single 7Ah lead acid battery  (almost 5 hours and consumed 4,1 amps for both heaters and the controller).
Got one spare battery with me but didn't need it.