kbrown

8 hours ago, BCN_Sean said:

I've seen similar behaviour with other temperature sensors before, one of them on the AF units I've built (can't remember the model number off the top of the head) and this may muddy the water a bit for you, but what I traced some of it down to was the 5v line being unstable; so whilst the motor was racking in and out, there was a voltage drop on the 5v which in turn messed around with the calibrated (startup) reference value so the sensor was thinking that the air temperature had changed because of that.

In the end I moved that one off an Arduino on to a Wemos D1 Mini as that's the only dev-board I could find that didn't jack around with regulators and current diodes between the USB Vin and the 5v rails.

Good to know. I intend to run this off 12V mainly. Of course the Arduino will turn on with just the USB connected but I monitor the 12V with one of the analog inputs and won't be doing anything crucial if the 12V is missing. With the 12V going into the Vin I should get pretty stable 5V off the regulator onboard the Arduino.

I repeated the above test with the changed electronics and code so that I only turn on the DHT22 for two seconds once every minute to take a reading. The results are much better. I ran it this way for two hours and got only about 0.2 degree variance on the temperature reading.

11 minutes ago, BCN_Sean said:

Here's the datasheet for it https://www.sparkfun.com/datasheets/Sensors/Temperature/DHT22.pdf, according to that, it should have it's own low power state modes.

Yes I have seen that. But I have also read others observing the same sort of self heating problem. Maybe my DHT22 is bad/old/whatever, but it's definitely not reliable if powered on constantly. Here's a test I just ran:

I started taking readings just after powering on the device. I took subsequent readings about 15 min intervals. About half way through I turned off the device and only turned back on again momentarily to take another reading. The room temperature was stable throughout the test and I'm pretty sure the relative humidity didn't change this much either. From the graphs you can see a clear (sorf of logarithmic) rise and fall of the temperature readings and the relative humidity seems to follow this inversely.

I've just changed the electronics and the code so that I can just turn the sensor on for taking a reading then turn it off again. Seems to be running just fine powered from a digital output of the Arduino. I'll repeat the above test...

Thanks for the information and ideas guys. Think I'll drop the whole elevation calculation down in my priority list as it really isn't needed here.  I was just curious what I could get with the BMP280 sensor. TBH I don't even need the atmospheric pressure reading for anything else other than logging.

I have a new problem though that is relevant to this project. The DHT22 sensor I'm using seems to be another source of problems. Looks like it's self heating when powered on continuously. I get fairly accurate readings when I power the device on but after about 15 minutes it's already off quite a bit. Shame I didn't notice this before I had the PCBs done. Suppose the solution would be to only power the sensor on when reading it. I don't know what the power requirements for it are. I'm hoping I could power it directly from one of the Arduino digital output pins. That way I could just hot wire it without changing the PCB.

I managed to get it to calculate an approximate elevation based on the absolute atmospheric pressure reading I get from the BMP280 sensor. However it relies on the knowledge of the current sea-level pressure. It seems to be fairly inaccurate if I just use the average sea-level pressure of 1013.25 mbar as stated on this wikipedia page. Yesterday it was saying I'm at 150m and today it's saying I'm at about 90m. https://whataltitude.com/ says I should be at about 28m (30m resolution) so the whole altitude measurement seems to be pretty inaccurate in principle (correct me if I'm wrong).

Not that it really matters in my application (I won't be using the elevation information for anything other than displaying it) but it would be nice (=geeky) to get this working a bit better. So my current thinking is that I send the current sea-level pressure to the device from the INDI driver which would get this information online. Here lies my question: where can I obtain this information from? I know it is broadcast somewhere as aircraft pilots use it. Has anyone got any insights on this?

It's finally assembled. Hope I don't ever have to take it apart again. Took me a while to get everything fitted in there and connected. Still need to write the proper firmware for it but I've already verified all the inputs and outputs work and I can read the sensors.

At this end from left to right: Ambient temperature and humidity sensor, Reset button, USB connection, Power switch, Power out and in, Fuse.

At this end there's the heater outputs, temperature sensor inputs and indicator LEDs for the heaters.

This is actually a project I started back in 2015 but it's been hibernating on the shelf for a number of years (i.e. way too long). Up until now I've been just running my dew heaters full on without any controllers whatsoever. This has not caused me any trouble until recently. I changed the secondary mirror on my Newtonian to a bigger one and also the way it was mounted and heated. It turned out that heating the secondary this way full blast is not a good idea as it would warp the mirror ever so slightly to cause astigmatism.

Anyway, here I am trying to complete a project that is way overdue... My idea is to measure the ambient temperature and relative humidity with a DHT22 sensor and calculate a dew point from that with an Arduino which would then in turn control a number of dew heaters (max 4) while measuring their temperatures. The idea is that with empirical experiments I could come up with reliable offsets to keep the optics a couple of degrees above the dew point to prevent fogging. How successful this is going to be; I have no idea...

 As a bonus the device will also measure the atmospheric pressure.

Some photos of where I am at the moment:

Here's a KiCad 3D preview of the board(s) I designed

Decided to have the PCBs made by JLCPCB for me. The minimum order with them is 5 pieces so if this turns out to be a successful project, I'll have four extra PCB sets available. PM me if you're interested...

Here's the real deal soldered. Not too far from the 3D preview

All wired up ready for testing and further development. I intend to make this into an INDI device as well so I can log the measurement data...

Like others have already pointed out, vero boards are an option, if the circuit is fairly simple. Have a look at this: https://veecad.com/

It's a handy vero board designer that can take a netlist from KiCad for example and you can plan the vero board (fairly) easy.

I have made PCBs in the past and I have also used JLCPCB. Both have pros and cons. Last time with JLCPCB I got caught by customs fees (prior brexit) that took me by surprise. It's still a lot easier way of getting professional PCBs done without the hassle and mess.

Yet at the moment I'm planning to make a PCB at home mainly due to it being a bit of a challenge mechanically. I have a CNC router which I will be using to drill all the holes and mill the outlines with. For etching I laser print on Laserstar film and UV expose it with an old facial solar lamp on a pre-coated photoresist PCB. Then develop in slightly warmed up developer solution and etch with ferric chloride. My ferric chloride is in a plastic container with a fish tank heater and pump to keep the solution warm and moving which accelerates the etching process. It is a lot of work and messy I have to be honest. I don't like doing it unless I have to.

You can see one of my PCBs here. Another thing to keep in mind is that doing double sided PCBs is a lot trickier than it sounds. I often design my PCBs as double sided but use the top side sparingly and replace all the copper tracks on it with jumper wires.

13 hours ago, Chriske said:

Oops ...!  looking bad that heating system. How hot does that thing get...?  (about)

13 hours ago, Chriske said:

Remove that sheet of alu.

You can now continue without that heating system.
If you hold on to that heater you need to soften the aluminium to get rid of that strain.
I'll explain later how, it is not the same as softening metal...!!
The silicone blobs should be much smaller and very near the edge, almost peeking out of the perimeter of that SM.

I've had the heater on for couple of hours now while monitoring the temperature of the backing plate and the surface of the mirror. At the beginning both were at 18.9C and after a couple of hours later the plate was at 50C+ (oops !!!) while the surface of the mirror had only gone up to about 21C. Clearly this is not the way to go... I was going to build a closed loop heater controller (to keep the plate only a certain amount of degrees above dew point). But now seeing how inefficiently the heat is transferred to the other side of the mirror, I'm not sure if this is a good idea anymore.

6 hours ago, Chriske said:

And one more thing. Maybe you already removed the alu sheet. If not, While cutting, leave the silicone blobs on the SM.

I haven't removed it yet. I'm sort of reluctant to do that now as it does work without the heater. Out of curiosity why would I leave the blobs on the SM?

3 hours ago, Astrobits said:

In addition, the radiant heat from the heated Al will warm the back of the mirror more than the front putting further stress onto that back and causing more curvature of the mirror,

 

I think this might be the main culprit here given how much hotter the plate gets compared to the opposite side of the mirror...

3 hours ago, Astrobits said:

To prevent dewing the mirror(s) should be shielded as in a solid tube (or shroud for open truss designs).

Nigel

Hmm... haven't seen a design like this in a classic newt but I suppose it makes sense. Mine's a basic steel tube Sky-Watcher 250P.

@Chriske I managed to find out what alloy my Alu sheet is. It's 1050 H14 so it's pretty soft already. For 1xxx alu this page says: "Non heat-treatable. Technically annealing is possible, but it’s really hard and best avoided entirely unless absolutely necessary. To be honest, this stuff is so soft that it’s really unlikely that you’ll need to anneal it unless you’re really stretching and compressing it.". I'm not sure if I'd want to try to treat the plate I currently have since I'd probably have to strip the super glue and paint off as well. If I go down that route then I think it would be easier if I just milled a new plate. I'd be keen to hear about your method of taking the strain out of the Alu?

6 hours ago, Chriske said:

Carefully place the flat agianst the SM and see what result you got.
See that there are no dust particles between SM and reference flat...! do  not remove the alu-sheet at this point.
take a picture of that result.
Next remove that aul-sheet, and do exactly the same.
Compare these two pictures and post them both here please.

This way you can eliminate possible problems of that alu-sheet.

I did some testing tonight but was reluctant to remove the SM from the backing plate just yet as I wanted to show this first. Here's the optical flat on the SM at ambient temperature under green laser light. Doesn't look too bad as far as I can tell.

Then without moving the setup at all I turned the dew heater on and waited about 20 minutes. Here's what I got:

As a sanity check I then turned the heater off and waited again about 20 minutes and it returned pretty much were I started:

So it's definitely heating the plate like this causing the warping. I tried to take a photo of the silicone blobs I've put in. Do you think these are too big in diameter?

5 minutes ago, Chriske said:

Ok, some issues can be eliminated after that last post.

You need to concentrate on that SM or it"s holder.
a few possibilities there.

Before we go to removing strain out of that sheet of alu...this is most important not to do that yet.
You need to rule out some possibilities first.

- Do you have a reference flat..?
-Do you have a Foucaulttestes and know to use it..?

I now do have a reference flat. I posted some results on this thread back in November (go back to previous page). I started building a focault / ronchi tester as well ages ago but unfortunately I haven't finished it yet.

3 hours ago, Chriske said:

You need to adjust the heat to just one, or two degrees above ambient. Just enough to keep the dew away from that SM.

But as your SM has already astig, when cold, there's another problem. Looking at the surface of the aluminium I think that sheet of alu is most probably hardened alu.
Meaning that sheet of alu is full of strain. That has to be removed first. Now as it is heating that sheet of alu the tension in the alu get worse and pulls on that mirror. You need to remove that strain by softening the alu. Sadly enough you need to remove the mirror first from that sheet of aluminium.
If you do not know how let me know.

BUT what I do not understand is why the ast has a perfectly elliptical shape. Maybe just maybe it has nothing to do with that hardened sheet of alu. at all.
First this :
Are you ab-so-lu-tel-y sure that both these mirrors are free of astigmatism...!!!  Maybe in the past you didn't notice..?
Can the primary mirror move freely in it's holder. Just a fraction of a millimetre is enough. The clamps/hooks (to hold the mirror down), are they not to tight.

Make drawing please, were are the silicone blobs located..? It's not a major issue, but it could reinforce the error you're dealing with right now.

Sorry for the confusion. No I don't think the SM has astigmatism anymore when cold. I think the previous astigmatism I had was due to the way I had it attached to the holder. With the new backing plate and three blobs of silicone that issue seems to have resolved itself when cold. Here's a 9 frame animation going from extrafocus to intrafocus with the SM cold. The collimation isn't perfect here though.

Here's the same exercise with the heater on:

1 hour ago, Chriske said:

If the backing plate is warping then it should not distort the shape of the mirror, as you said Nigel. That is correct. But what about the size of the blobs..? I'm afraid (tell me If Im wrong here kbrown) that the blobs are not to big. That's why I asked before to make an estimate drawing about that.
Heating a mirror, be it Pyrex, Duran or any other decent glass it should not deform at all, by the heating it that is. That's what all these types of glass are suppose to do, hold its shape when cooled or heated.
And btw 1 or 2 degrees should not warp any mirror at all.

Let's first find out what kbrown has to say about the quality of his mirrors.

First : Make a picture, same as above, turn he primary mirror 90° around it's optical axis in it's holder and make a second picture holding the same position of camera and scope. What happened with the pattern.? Did it hold it's position or not...?

Here's a rough drawing indicating the location and size of my silicone blobs. Maybe they are too big?

I have checked the primary mirror and its holder multiple times in the past and made absolutely sure it's not pinched or slopping. I have also done the rotate around optical axis test and it did not affect the pattern.

@Chriske How would you remove the strain out from the aluminum plate? Heat it up slowly in boiling water or something then let it cool down on it's own (with the water)?

45 minutes ago, Chriske said:

Hold on,  you're saying(if I understand it correctly) : no heating and there's practically no astigmatic error at all ..

?

Yes, that's correct. With the heater on it slowly starts to show astigmatism again. I guess the heater causing the backing plate to bend slightly which in turn deforms the mirror. I haven't got a controller on the heater so it's always either on or off...

Gosh this is a lot more finicky than I ever thought it would be. I'm nearly there but....

So I went ahead and milled a matching size backing plate out of 3mm aluminum for the secondary mirror as per the idea in one of my previous posts. I also routed a channel for a dew heater wire on it:

Before gluing the heater wire in the channel I applied several coats of paint to act as the electrical insulation so the plate wouldn't short the wire. Here's the wire in place with some super glue dots:

#

I haven't got a photo of the finished thing but essentially I just filled the rest of the channel with industrial grade HV super glue. Then I attached the mirror onto the other side of the plate with three blobs of marine grade silicone with a 3mm gap between the plate and the mirror.

Everything seemed to work just fine except I can't really use the heater. Without the heater on, I get near perfect images with practically no astigmatism at all. But with the heater on, it starts to warp the mirror enough to get oval shaped stars. Here's an out of focus example:

So my main question here is; How to heat the mirror up without  warping it?

So I was experiencing some newton ringing with my solar imaging setup. To remedy this I thought I'd try the DIY route an make myself a simple camera tilter. Turns out it works good enough.

More about this and STL files available on my blog post.

Just to let you know I have started to look into writing an ASCOM driver for this but my lack of ASCOM, C# and Windows .NET development experience means that it is going to take some time to get there. At the moment I can't even get the basic template stuff to compile without issues (what have I gotten myself into?). Could be months before I'll have anything usable available...

3 hours ago, dazzystar said:

...and, the only UK distributor for the driver board, despite typing in their search bar for tmc2209 keep coming up with this https://e3d-online.com/products/genuine-watterott-tmc2208-stepper-motor-driver-heatsink?_pos=1&_sid=07b3dc72f&_ss=r which is a tmc2208. Again, no idea if there's any difference. Where did you get your board from Kari?

I got mine from farnell: https://uk.farnell.com/trinamic/tmc2209-silentstepstick/stepper-driver-board-2-ph-motor/dp/3131532?CMP=i-bf9f-00001000

Looks like they're out of stock at the moment though...

46 minutes ago, dazzystar said:

Yes. I've added the libraries and was under the impression that the INDI driver was the program that needed installing on the Nano. It looks like my complete lack of coding and scope knowledge has let me down and fundamentally this won't work with a PC running NINA as there's no software for it. Thankfully most of what I purchased came from Amazon so can go back but I'll have a stepper motor arriving after Xmas which isn't needed as well as a 3D printed enclosure...any takers?

No it's the firmware you load onto the Nano: https://gitlab.com/kbrown/bullseye-focuser/-/tree/main/firmware/bullseyefocuser_actuator

Just open the .ino file in Arduino IDE and upload it.

The INDI Driver runs (with INDI server) on your PC or RPi or whatever you're using to control your rig. Then you connect to this with an INDI client such as KStars / Ekos.

20 minutes ago, dazzystar said:

Thanks very much but seeing how easily I screwed this up I'm going to buy an autofocuser. I thought I could do it but clearly I was so so wrong. The AF was the last thing I was going to save up for as I need a camera and mini pc first but the DIY route looked fun and quite inexpensive. The Bullseye model, if working on a PC with ASCOM and NINA would be incredible and I think doable for me but hey ho....merry Xmas everyone!

That's a shame but I do understand. Might be a bit of a hurdle to get it all working if you haven't got previous experience. It wouldn't be impossible to write ASCOM drivers but I have never used them so I lack the knowledge to do so. Happy to help if anyone fancies the challenge?

3 hours ago, dazzystar said:

Just looked closely at your schematic. It says SilentStepStick v2.x but the one I ordered from Amazon has v1.2. Is this going to be a problem do you know?

Looks like the pinout on your board is slightly different from mine so you'll need to be careful where you're soldering your wires!

4 hours ago, dazzystar said:

Thanks for the reply. I intend to upload the code (once I've measured and put in the figures for R3 & R4) to the bare, unmodified board then build it. Assume that'll be ok. Although I ordered the exact Nema 17 motor it doesn't look like it'll arrive until after Xmas now. I did order this from Amazon yesterday just in case, will it be okay? https://www.amazon.co.uk/gp/product/B07FKH52S5/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

 

That should work and should have plenty of torque. You'd definitely want to use a heat sink on the stepper driver if you're running it with high RMS currents.

3 hours ago, dazzystar said:

Speaking of entering in the values for R3 & R4, do I do this once I've connected the Nano to my PC and get the IDE console up and hopefully loaded with your code or do I need to do something else (never done this before!)

You can do this at any stage before uploading the code to the board.

2 hours ago, dazzystar said:

Just looked closely at your schematic. It says SilentStepStick v2.x but the one I ordered from Amazon has v1.2. Is this going to be a problem do you know?

I don't know to be honest. I don't even know which version I have. It doesn't say on the board and I can't remember where I got that version number from 😕 Don't think there's any massive differences...

46 minutes ago, dazzystar said:

The bi-colour LEDs I ordered are common cathode, can I still use it and if so what wires do I need to change?

You'd have to change a few things. You'd connect the common cathode to ground and the anodes to D10 and D11.  You'd have to change the code too to invert the D10 and D11 outputs.

3 minutes ago, dazzystar said:

The Nano has just arrived and I've plugged it in to my PC but I have absolutely no idea what to do now so any help would be really appreciated.

Might be a good idea to read about Arduino in general to get a feel for how it all works. Do a simple blink example and get it working.

4 hours ago, dazzystar said:

Thanks. I've downloaded and installed the Arduino software on to my Windows 11 PC and have hopefully installed the dependencies from https://kbrown.gitlab.io/bullseye-focuser/actuator/html/

The Nano hopefully arrives tomorrow. Can I load your code on to it straight away or do I need to basically build it first? Is it simply a matter of connecting it to the PC via USB or do I need to power it as well? Is it straightforward enough to use the code given in https://kbrown.gitlab.io/bullseye-focuser/indi-bullseyefocuser/html/ via some kind of console screen?

Cheers

Daz

2 hours ago, fozzybear said:

nope if testing the software compile/upload on you arduino then no external power required, else testing the motor then yes

Yup. Arduino IDE will automatically compile the code before uploading so no probs there. USB power is enough for powering it for programming.

Be sure to read the notes here especially about the C1 cap or you might run into some trouble.

6 hours ago, dazzystar said:

Brilliant. Just a few things left to order, 10uf, 1uf capacitors, I assume anything small and around 16v is fine. The bi-colour LED (having a nightmare finding them on Amazon), it's little holder and then a power socket...

Yeah. Anything small around 16v should do. In a pinch you could use two single LEDs. Just solder the anodes together and then connect the rest of it as you would do with the bi-colour LED. Might be a good idea to build a test version on a breadboard just to make sure everything works as expected before you do the actual assembly.

42 minutes ago, dazzystar said:

I've ordered these, will they be ok?

https://www.amazon.co.uk/AZDelivery-Atmega328-CH340-compatible-Arduino/dp/B01LWSJBTD/ref=sr_1_1?crid=1A7S92PA24F7L&dd=IRfUNZ1j9szT7EK_2UUcGw%2C%2C&keywords=arduino+nano+5v&qid=1640253527&refinements=p_90%3A22415809031&rnid=5381144031&sprefix=arduino+nano+5v%2Caps%2C81&sr=8-1

https://www.amazon.co.uk/PoPprint-TMC2209-Stepper-TMC2208-TMC2130/dp/B07ZNGHRJF/ref=sr_1_6?crid=2JOCZSW37IJ6B&keywords=tmc2209&qid=1640253738&sprefix=tmc2209%2Caps%2C82&sr=8-6

 

These should be fine. The heatsink on the stepper driver might be a bit too high for the enclosures I've designed but you could get another one later. Or possibly you might not need one at all if you're only running your motor at low RMS currents,

31 minutes ago, dazzystar said:

I've also just ordered the motor from stepperonline. Hopefully will get it all tomorrow. Just need to order some caps now. Can I assume that I don't need to use the temperature probe if not required?

 

No the temperature probe isn't required for this to work.

4 hours ago, dazzystar said:

Hi,

Being quite new to this type of thing I've seen on Amazon quite a few Arduino Nano's and am not certain which to get or would any one of them be ok? It appears most of them have pins already soldered to the board which I'm assuming is a no-o and would have to be removed. I'm trying to get hold of as many of the parts from Amazon as I can for speedy delivery. As for the stepper motor is concerned must it be that exact make and model number or would something else suffice? 

Cheers

Daz

Just make sure the Arduino Nano is the 5V version, not 3.3V. I used cheap clones from fleabay. I'd get one without the headers soldered as desoldering them can be a pain. The stepper motor doesn't have to be the same make and model. I made two focusers using two different steppers. They do need to be bipolar though. Also depending on how you're planning to drive your focuser, the rated torque of the motor might be a factor.

3 hours ago, dazzystar said:

Also, the only TMC2209 I can find for fast delivery (before Xmas) says: TMC2209 V1.2 Silent StepSticks Stepper Motor Driver VS TMC2130/TMC5160 for 3D Printer Parts SKR V1.3/Mini E3 V2.0. It also comes with pins soldered on the board! Is this ok?

 

I might be wrong but I don't think my code would work with any other silent stepsticks than TMC2209 based. Desoldering the headers off these might be a bit easier than the Nano as there's fewer pins on each side of the board. I got my boards from uk.farnell.com. Might not be the best place to get them from unless you have other things to order to justify the delivery fees...

6 hours ago, rsarwar said:

I could. Should not be difficult at all. However, how do you change focus on the Cs mounted lens?

I didn't really bother doing much with the focusing. I just set it manually to where I thought I'd see enough. I used this mainly for centring and aligning the secondary mirror on my newt after taking it out. Really handy for that. Then I used a laser collimator and a chesire eyepiece to fine tune things. Iterated the whole process a few times and I got a very good collimation.

Great job. Are you planning to release your work to the public? Been thinking of doing something similar every now and then...