kbrown

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.

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.

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

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?

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.

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. Blink.avi Here's the same exercise with the heater on: Blink2.avi 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)?

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...

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... 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. 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?

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!

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

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.

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.

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

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. 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...

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...