Arduino dew heater control

[JAS]

Nice one Phil, good luck!

How about a led linked directly to the 12v in, via a resistor of course. To give a visual indication that you have power?

Jason.

[IanL]

Was just browsing the Maplin Christmas catalogue whilst waiting for the computer to start up when this caught my eye:

http://www.maplin.co.uk/electric-heated-hat-531712?c=maplin&utm_source=gcs&utm_medium=gcs_search&utm_campaign=N62KA&utm_content=Outdoor+Heated+Clothing

If anyone has some spare nichrome left over, I reckon I've found the perfect use for it! Though maybe using an Arduino and a temperature probe would be taking things a bit too far?

[philr]

Hi Jason,

I did in fact hook up an LED, so that gave a positive indication of what was happening.

However, Replacing the contrast pot got my LCD displaying data again. I was then able to get on with checking the duty cycle, which is operating correctly now. I should soon have the DC adjustable for each output.

I've had it all running tonight. The heaters are are all working properly, I have just tweaked the code a bit to correct for the DHT under reading by 2.3 degrees C (according to my digital thermometer). Because of the under-read, two of the heaters were not driving the temperature up enough to control the dew. I will also need to re-make 2 heaters as they are clearly under powered. Its just as well I have a lot of nichrome wire and sleeving.

Hopefully, I'll have it all set up again tomorrow night for further trials - if it isn't raining!

How is yours coming along?

Phil

[JAS]

Glad to see you have it sorted Phil.

I ran all 4 heaters yesterday afternoon at max power for 4 hours just to simulate a malfunction, nothing melted or even started to smell hot so I am happy to keep the heaters as they are. I am adding control for the cooling fan on my OTA today. I am thinking 100% until the primary reaches ambient temp then I will try it runing at the slowest speed possible for the rest of the night and see what happens.

Jason.

Sent from my LT15i using Tapatalk 2

[philr]

Well done Jason, sounds like you have done a very good job of it. Its very satisfying when things go well.

I tweaking the DHT temperature correction by 0.5C at a time, to achieve agreement with my thermometer, now within 0.5C. So its now running with all heaters connected, waiting for the dew trigger point; its close.

Last night the correction was wrong, meaning the the heaters came on at below dew point, not a lot of good like that. Have you been able to check your DHT22 for accuracy?

Isee that you have a modded 100D. Did you encounter any problems doing that job? I'm thinking that in the New Year, I'll buy another used body, probably 450D or 1100D, and mod that myself.

Good luck with the rest of your testing. You're doing well.

Phil

[philr]

Well, its working as designed, and very well too. I only had to tweak the temperature differential up a couple of degrees for the SCT, since it is the one radiating the most heat out to space.

I'm going to re-design the strap for the SCT though, to make wider and better insulated, and thus more efficient. Currently its quite narrow, leaving a lot of the corrector plate mount exposed to radiate heat away.

Very gratifying that the long hours have paid off.

There will be one or two additions to make, but I can soon say its done I think. Once I'm completely happy I'll write it all up and post the sketch and libraries.

Thank you for your suggestions folks.

More anon.

Phil

[Gina]

Well done Phil

[philr]

I have now re-made the SCT strap. Its now the full width of the corrector plate mounting, and thermally insulated from the outside. I've also fixed the Dallas inside the front lip of the corrector plate mounting. This means that it measures true temperature rise and is not influenced by the heater strap.

I now have an LED fitted to each output, so I get instant indication of which straps are on.

The last thing to do at the this point in time is to take the DHT22 off the box, fit a 3 pin connector, and mount the DHT22 at the top end of the SCT. To be thermally insulated from the scope and facing downwards so dew cannot get on the sensor element - they do not like dew on them.

I'm going to give a few weeks of testing to see whether individual duty cycles are warranted. They probably aren't if the heater straps are correctly matched - we'll see.

Phil

So now, given clear skies I can start to concentrate on some imaging, and let automation look after the mundane tasks like dew control.

[milosz]

Hi,

I just finished soldering my controller today. I'm testing it now outside. It seems that the DHT sensor cools down really slowly comparing to DS18B20 thermometer. See the picture:

'T' and 'H' come from DHT22 and T1 comes from DS18B20. I don't have the code that controls the heaters, but I hope to have it done tomorrow (if the wires are correct). Keep fingers crossed!

Gina, many thanks for the drawing! It was a big help.

milosz

[milosz]

50 minutes later:

Now the readings are quite close. I'm wondering if the temperature reaches the dewpoint tonight.

milosz

[JAS]

I am also testing mine tonight.

I have been imaging since 7 and everything has stayed nice and clear. I have not found my DHT22 to be slow, I have found it to be reasonably responsive?

Jason.

Sent from my LT15i using Tapatalk 2

[JAS]

How are your tests coming along Phil?

I have been out for 4 hours so far tonight and all has been running well . I have added control of the cooling fan on the back of the tube, but I havn't tryed it yet. also

I added a overheat warning buzzer just in case!

The temps are not even close to the dew point but I am in for a late one tonight so may be it will happen later.

I did mod my 1100D using a Badder filter, following Garry Honins's guide, it was very straight forward the only thing that was not so easy was geting the ribbon cable for the rear display into place.

Jason.

[philr]

Hi Jason,

Well, I've used it in anger for three nights now, and no dew!! Its nothing short of miraculous, I'm very, very pleased with how responsive it is.

I have now mounted the DHT22 remotely from the box, its fixed at the top of the SCT on thermal insulation, so its only reading what it should be reading at the most critical position. I've seen people suggesting mounting in side the box - that makes no sense at all, since it would not be able to detect what is actually going on in the big bad outside world.

What I do now is plan well ahead and switch the Arduino and heaters on a good two hours before observing, doing that means the glass has all stabilised to the correct temperature. I've never had such good clear seeing.

Just picked up an excellent Canon 450D on fleabay. Almost new condition and a lot lower shutter count than my existing one, so swap about ready to mod the old one. Have just ordered the BAAder filter and have read up Gary Honis' stuff, seems quite straight forward - given a lot care. That should completed in the New Year.

Getting to grips with BackEOS; an excellent program.

So, things are looking good.

Phil

[JAS]

I am using BYEOS too and it is the best thing I did. I stayed out until 3 this morning, although the dew point was not reached the scope was totally covered in frost but the heaters kept everything nice and clear. I even managed to get 20 minute subs!

I agree with letting everything equalise, I started the heaters up an hour before I went out last night and it all worked out well.

Should have it put into the hub this weekend.

Jason.

Sent from my LT15i using Tapatalk 2

[philr]

Good stuff Jason. I too would have been in the dome to the early hours , had it not been that I had to be up a 0500.

Bad weather coming in it seems - oh well.

Phil

[JAS]

I know what you mean, I managed to arrange to start work late so I could take advantage of the clear night, they are hard to come by these days.

Jason.

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[Gina]

So Phil - without re-reading all through this thread, do I gather you're using one DHT22 to calculate the dew point and then setting the temperatures of the dew heaters to just above that? I ask because you have a good working system that I think I will emulate (in spite of being the instigator of this thread ). My present dew controller box uses the Chinese LED strip controllers but one has gone caput and I want 4 altogether. I have a stock of logic level controlled power MOSFETs so a little box with an Arduino in it attached to the dovetail would reduce the wiring mess considerably.

I guess I should read through this thread again really

[philr]

Gina, yes one DHT22 remote from the box. I can set the heaters individually so they are about 2 to 3 degrees above dew point. The actual temperature set in the sketch is not necessarily the real difference measured at the SCT, EP etc. Because of they way the heat disperses, I found that with the SCT for example, the difference in the sketch needed to be 8 degrees; sounds a lot but in fact that works. Its very much a trial and error thing to find the balance.

I can send the sketch and libraries as they are if you like, or wait a bit until I have some of the code sorted out. As I based mine on the 'mitaccio' scheme, it still has Fahrenheit conversions in it. This means that there is a conversion from F to C. So the LCD readout is correct. However, when using the Serial Monitor in the Arduino IDE, the readout there is still in F: its this that I will re-do shortly. It doesn't make any difference in practice, but it would tidy things up.

[JAS]

I found the same thing Phil, my ota is also 8 degrees above where the guide scope is 5.

Jason.

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[philr]

I am now about to try my modded code for individual duty cycles. At this time they with have to be set from the sketch. However, they may be a BlueTooth mod coming along for remote control of the variables.

More later.

Phil

[JAS]

I was looking into Bluetooth but have moved onto looking at control via the pc. I am using a remote desktop from my shed and Bluetooth would not have the range, a small window on the desktop with the same info displayed on the lcd and perhaps some duty cycle control would be nice. Just not sure where to begin.

Jason.

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[George]

Been following this thread on here and Cloudynights avidly, the last of my bits should be here next week so I can have ago myself

[JAS]

Good luck George

[philr]

Well, my setup is still doing what it is supposed to do. The only thing I'm not happy with is my LCD. The data scrolls, but the LCD latency is awful, meaning that it can be hard to read. So I'm looking for one that behaves itself. Sparkfun in the USA sell one, but I can't track it down in the UK. I've found a different one that may work, just waiting for an answer to my query.

My sketch and library is attached. It still has all the temperature conversion lines in it. However, it works, so I'll probably leave it alone - for the time being anyway.

Phil

dew_control.zip

[Gina]

I have decided to go for the Arduino dew heater controller. The ultra cheap LED strip controllers I got from HK have gradually been dying and I no longer have enough to control the 4 dew heaters I use. I also like the idea of automatic temperature control.