Robert Brown Arduino dew controller build, step by step

[JamesF]

Nice idea, Robert.  It had struck me this evening whilst looking at the circuit diagram that there's no real difference between the fan circuit and the dew strap circuits, but didn't occur to me that it might be used in such a way.  I shall bear it in mind if I decide I need four channels one day.  I must check what the internal temperature of my first controller is.  It's been running for about four hours now in an ambient temperature of about -1C.

James

[JamesF]

The current PCB temperature is being reported as 10C.  I think it has been pretty close to that all evening.  Ambient temperature is still fractionally above -1C.

James

[brown_rb]

27 minutes ago, JamesF said:

The current PCB temperature is being reported as 10C.  I think it has been pretty close to that all evening.  Ambient temperature is still fractionally above -1C.

James

If you enable logging then the pcb temp etc should be logged to file and then you can view that later in myLogViwerPro to see how it changed over time.

[brown_rb]

-1 is cold for me. What is your location?

[JamesF]

South west UK

James

[JamesF]

I think my work here is nearly done, but before I post about testing I realised I've not actually mentioned the temperature sensors.  As I said in a previous post I decided to go for 3-pin GX12 plugs and sockets for the sensors.  This is what they look like, completely with dust covers.

The sockets were much easier to work with than the 6P4C sockets for me both in terms of the case layout and soldering up the connections.  The plugs were equally straightforward.  The black connector part unscrews from the metal body revealing the pins for connecting the wires, so it's just a case of loosening off the cable clamp, feeding the metal body onto the cable and then soldering on the wires.  I found it necessary to add a couple of turns of insulting insulating tape around the cable to give the cable clamp sufficient to bite on, but otherwise reassembly is just a case of screwing the metal body back onto the black plug (hold the plug so the individual wires don't get twisted inside and perhaps touch each other or get damaged) and doing up the clamp once again.

And here's one I made earlier.

James

[JamesF]

It's about time I finished this thread off.  So, a bit about testing.

I downloaded the arduino code from Sourceforge and unzipped it to find a directory called "Tests", which seemed quite straightforward.  In the documentation there are a list of tests n the order they should be run, but I think it actually works out that the subdirectories of "Test" are arranged so that they're in the correct order when listed alphabetically.  The first was "TestBlueTooth" which I skipped as I didn't build the Bluetooth interface and moved straight onto the second, "TestBoardTempSensor".

I'm a Linux user and I had the default set of Arduino tools already installed on my Mint 19 desktop system.  There is a "Readme.txt" file in the Tests directory that talks about where to put the various library files for Windows, but no information for Linux so I decided that initially I'd just try compiling things and see what happened.  I plugged the dew controller USB connection in, set the correct board type in the tools and made sure the device name was /dev/ttyUSB0, but even so what happened was a horrible mess of errors.  That led me to download the latest version of the Arduino tools from the Arduino website and try again.  Better, but still no cigar.  It did create a subdirectory of my home directory however, called "Arduino/libraries", so that seemed a reasonable place to put the library files.  I copied all the subdirectories of the unzipped "myDewController Libraries" directory into that and tried compiling again.  Success!

From the Arduino IDE tools menu I opened the serial monitor and uploaded the sketch.  In the serial monitor I was rewarded with:

I followed the same process for "TestDHT":

and "TestDSB1820TempProbe":

(I've just noticed that is in fact out of sequence).  From then on it's a little more complicated, and requires that the 12V supply be plugged in and switched on.

"TestFanandLEDs" runs the fan at various speeds and sets the RGB LED to each of its possible colours, so that's a visual check.  As noted already this didn't work for me and close inspection of the PCB showed some soldering I wasn't happy with.  I so hate having old eyes   I redid the soldering and it worked once reassembled.

"TestLCD" displays a message on the LCD screen.  The display I used for this build worked perfectly first time, but on my first build I had to adjust the brightness using a small adjuster on the back of the display.  It's the blue component in the top right here:

If you're nervous, disconnect the power and USB, adjust it and then reconnect everything.  Or use a plastic-bladed screwdriver to adjust it.  Or, like me, just go for it with a normal small steel-bladed screwdriver and be very careful not to short anything out.

The last test I ran was "TestPWMOutputs", which sets the dew heater outputs to 0%, 100% and 50% in turn.  The dew strap indicator LEDs should change brightness at the same time.

With all the tests passing I set the controller up on the mount and connected everything up, including a USB connection to my pier-top computer which allowed me to run the Linux "myDewControllerPro3L" application to monitor the controller and adjust the settings.

After my first night using the controller I noticed that dewstrap 2 was on according to the LED, but not warm.  I brought the unit inside again and found that even with that channel full on and the LED lit, there was no voltage across the dew strap connector.  As the LED and dew strap are connected directly together on the PCB that pointed to a connection problem between the PCB and socket.  I opened the case up to discover that the socket I'd plugged into the PCB for the dew strap connector had one of the pins pushed back out of it so there was no connection.  Clearly I'd not put it in properly the first time.  I made sure this time, replugged it and now everything is working as it should.  I'll put it back on the mount tomorrow.

Edited January 25, 2020 by JamesF

[JamesF]

I think that's about all there is to say about the build itself.  Over the last couple of days I've built a third controller that I'm in the process of testing.  Once that's done I'm going to start looking at Robert's focuser controller with a view to fitting on to each of my OTAs.  I do also intend to build one more dew controller to go with my travel kit.  Depending on my experience with the focuser controllers I might actually make single box containing focuser controllers, dew controller and RPi to reduce the number of things I need to carry around, but without an LCD display and probably the dew strap LEDs.  I will need to keep the fan I think.

I think I will probably also swap my first controller from the 6P4C connectors for the temperature sensors to GX12 plugs, but there's no real hurry for that.

Another thing there's no urgency over is the possibility of an improved design for the temperature sensors themselves.  The ones I have (which I believe are the ones recommended) have the sensor inside a metal barrel about 60mm long and 8mm in diameter, which isn't always the most convenient shape to use on a small OTA.  I've been wondering if I could use the DS18B20 case style that's used for the board temperature sensor and perhaps epoxy it to a small piece of stainless steel sheet.  With the wiring I think the entire sensor end need only be about 10mm by 30mm which might be more practical for small OTAs.

Actually, that's probably something else worth mentioning...  Attaching the temperature sensors.  I've no idea what the best way to do it is, so what I have at the moment is a strip of thin camping mat long enough to go right around the OTA.  The sensor goes underneath that, and it's all held in place with a velcro strap, just behind the dew heater itself.

James

[fozzybear]

James,

Well done and a big thanks, mine is partially built went stripboard route but not had the time to finish it. will do some day... as other things taking up my time (My son's new gaff Decorating DIY etc....) I believe you may do the focuser project as a little birdie has hinted and will follow that too.

Great job 👍

Andy

[JamesF]

Thanks Andy.  Best of luck getting yours completed.

James

[fozzybear]

4 minutes ago, JamesF said:

Thanks Andy.  Best of luck getting yours completed.

James

I'm 75% there just the ancillaries to do the fiddly bits as you mentioned as well a real pain if like me need specs to see close up or get my son to do the soldering (younger eyes)

again well done chap.

👍

[JamesF]

4 minutes ago, fozzybear said:

need specs to see close up or get my son to do the soldering (younger eyes)

I have to admit that whilst I've stuck with it and will continue to do so, this has been quite a frustrating aspect for me.  I ended up buying some +2 reading specs with fairly deep lenses from Amazon (actually I bought several pairs as I know I'll use them and will never remember to carry a single pair around with me) for about £4 each.  My normal glasses don't really help because I don't necessarily want to be soldering with my head at the same angle as I'd read at.  I have thought about buying one of those large "angle poise" magnifying glasses with the lights around the edge, but the price keeps putting me off.

James

[fozzybear]

James

I bought one of these

https://www.amazon.fr/Anpro-1-0X-1-5X-2-0X-2-5X/dp/B071ZVGBC3/ref=sr_1_8?__mk_fr_FR=ÅMÅŽÕÑ&keywords=loupe&qid=1580074303&sr=8-8

found it helped

Andy

 

[JamesF]

I'd seen those but didn't know if they'd be any good or not.  Maybe I should try one out since they're not that expensive.

James

[fozzybear]

2 minutes ago, JamesF said:

I'd seen those but didn't know if they'd be any good or not.  Maybe I should try one out since they're not that expensive.

James

works for me without my specs just got to find the x mag that suits and watch out when taking off as eyes get confused focusing

Edited January 26, 2020 by fozzybear

[Gina]

I've got an anglepoise light with 3x magnifier which I use for close-up jobs like soldering.  An essential tool in addition to reading glasses.

[fozzybear]

9 minutes ago, Gina said:

I've got an anglepoise light with 3x magnifier which I use for close-up jobs like soldering.  An essential tool in addition to reading glasses.

forgot about one of those they really do work should look out for one

[brown_rb]

On 11/01/2020 at 07:24, JamesF said:

And for the final bit of PCB soldering, the MOSFETs and voltage regulator.  The heatsinks I bought turned out to have small steel "legs" on when they arrived, which I didn't initially realise was the case.

I assume they're there so they can be soldered to the PCB and stabilise the heatsink.  And perhaps to connect it to ground.  There's no place for them on the PCB though, so I snipped them off with the side cutters.

Because there's not much room on the PCB for the heatsinks (some of the resistors prevent them from fitting flush with the PCB) I decided it was easier to put the whole thing together before soldering it into place.

Even then it was easier to put some of them into the board at a slight angle to get sufficient clearance.  An alternative might be to just saw 3mm or 4mm off the bottom of each heatsink.  I don't think it would compromise their performance that much.  And again I held them in place with a blob of blutak whilst soldering.  And here they are, all done.

To make much more progress I probably need the case printing, so I'll get that under way.  I'll also go over the back of the circuit board with a magnifying glass just to check there aren't any unintentional bridges in the soldering.  Then I'll plug in the Nano and at least see if it lights up and runs the default "blink" code ok.

James

James

A user (Mario) who is following your build asked a question about the Mosfets. It looks like some of those Mosfets are the wrong way round? The double bars on the silk screen indicate the heat sink or metal part of the T)-220 package.

 

[JamesF]

How odd.  It's in the observatory and working fine.  I think I mentioned that I didn't buy the suggested MOSFETs.  I had some others that looked as though they would do the job so I used them.  I assume they must therefore be in the right way for whatever they are.  I'll have a look if I take it apart again and see if I can see what they are and what package they use.

James

[arrayschism]

Re the MOSFETs, I bought the Fairchild, FQP30N06L types as suggested and they oriented as indicated on the silk screen.

 

[brown_rb]

Its possible that you used P channel mosfets instead?

[JamesF]

8 hours ago, brown_rb said:

Its possible that you used P channel mosfets instead?

Seems unlikely, but I'll find out when I get around to taking it apart again.  I'm going to build another at some point soon and I'll use the recommended MOSFETs for that as I've run out anyhow, in which case I'll replace the images with something less likely to confuse.

James

[wormix]

Great write up - I’m inspired to give this a whirl myself as I am in need of dew control for the coming winter. 

[wormix]

Have finally started my build - question on the toggle switches. The BoM calls for 3 pin SPDT switches, but the jumpers are only 2 pin. 
 

how are these supposed to be wired? 
 

cheers

[fozzybear]

43 minutes ago, wormix said:

Have finally started my build - question on the toggle switches. The BoM calls for 3 pin SPDT switches, but the jumpers are only 2 pin. 
 

how are these supposed to be wired? 
 

cheers

 "mini ON-OFF 3pin SPDT" then it will be most likely the middle prong and one of the outer prongs depends on which way you throw the switch to "power on" use a volt meter to check which way round you want to place the switch (on the continuity setting) just read Roberts PDF

strange as in the PDF quoted SPST on page 25

Two mini-toggle switches (SPST ON-OFF) connected via a voltage divider network provide an option of overriding the power setting to each dew channel to maximum (100%) when activated. If dew is forming, a sudden boost to heat the telescope optics is available by using the override feature. Just remember to turn it off as it does not turn off by itself. The controller implements overriding the power to the dew straps and applying 100% to either channel. There are a number of ways to do this. The toggle switches (only for channel 1 and channel 2), when ON, overrides the power calculation and applies 100% power to the associated channel (this is referred to as Override Mode). When the toggle switch is OFF, power for that channel is set to 0%, and then on the next power calculation the correct power will be determined for that channel (this is referred to as Normal Mode). The override switches could be omitted if the intention is to use the dew controller via computer, as the Windows application provides this feature (as well as the ability to disable the override feature after a time elapsed period at 100% maximum of 2 minutes).