Category: barn door tracker

Wow. It really works! Astrophotography!

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Well all the hard work has paid off. Here is a photo of the Pleiades.

After weeks of fully clouded skies days and nights… We had a clear night. And was I tired. I just went to bed.

I woke at about 4:30am, and went out and set up a reception experiement for weather satellite photos, and saw the sky was cool and clear…

So I brought all the equipment out to my back patio.. did a quick polar alignment with my red dot finder. Put the camera on and took a few test shots of a star.

It seemed to work for a 30 second photo… AND I focused by eye! The stars were so bright I could see them in the viewfinder.

And Oh Oh!.. There is Jupiter and to the left plain as day is the Pleiades, So I aimed the camera at it as best I could and took 12, 30 second shots… Stacked them… no calibration frames, cropped it and that’s what I got. Nice round stars!

Added a Beeper to the Barn Door Tracker

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Not that there will ever be a clear night in my area again.. I’ve continued to refine the barn door tracker.

So as I said in my last post.. the tracker will home itself now upon power up or reset. The process takes about a minute — mostly because the stepper won’t go more than 10rpm, and in the final homing stage I go 2rpm so I approach the home click slowly.

Well other than looking at the gears to see what direction they are spinning, which seems difficult if it’s dark out, also considering everything is in black plastic, I decided to put some audio feedback in the system. Now it beeps out beep codes telling me what it’s up to.

To do that I bought one of these, Fielect Active Buzzer Modules:

Click the image if you’d like to check it out on Amazon. If you decide to buy one too, and use that link it will help support this blog.

Now it came with no instructions, just labels on the pins, vcc, i/o, gnd. and some printing on the bottom saying it has a low trigger. Oh, and the buzzer itself has a sticky label on it that says “Remove after washing”… uhm… washing? At any rate, it seemed logical to remove the sticker since it covers up the sound hole of the buzzer.

So my assumption is, if I put a logic low on the i/o pin it will beep, and a logic 1, it should be silent. and I connected up power to 5 volts.. hey because I have a pin header where I can get 5 volts, and not where I can get 3.3volts.

Well that’s not gonna work… the ESP32 logic level 1 is 3.3 volts. Apparently that’s not high enough to convince the transistor on the unit to see logic level 1. So no matter what digital output, LOW, or HIGH I put out, it just constantly beeps. And it beeps loudly.

OK, so I’m lazy, I could unplug all the leads to the ESP32 for the tracker, solder on a pin header where I can get 3.3 volts to supply the beeper, and re-wire everything. What a mess.

So it was time for some hacking. Normally in Arduino land, you say “pinMode(PIN, OUTPUT). Then digitalWrite(PIN, HIGH) puts out 3.3 volts), and digitalWrite(PIN, LOW) puts out 0 volts.

But if you say pinMode(PIN, OUTPUT_OPEN_DRAIN) it does something else… digitalWrite(PIN, HIGH) floats the pin (in other words like no connection), and digitalWrite(PIN, LOW) grounds the pin.

Now that works. I can turn the beep on and off. But yes.. it is a total hack, that avoids taking things apart and getting out the soldering iron.

I did verify, using a different ESP32 I have which has 3.3v on a pin header, and the beeper works as expected. Configuring it as just OUTPUT, and sending out a LOW turns makes it beep, sending out a HIGH turns off the beep.

I’ve seen people online try to use Arduino tone() with these things, and yes that will make it put out different frequency tones, but an active buzzer is not supposed to be used that way.

Here is some code demonstrating both switching the beeper on and of — for a little blip of time, and then using tone.

// pins -- beeper vcc to 3.3v, gnd to gnd, i/o to io26 
#define BEEP_PIN 26

void setup() {
  pinMode(BEEP_PIN, OUTPUT);
  digitalWrite(BEEP_PIN, HIGH);
}

void loop() {
  digitalWrite(BEEP_PIN, LOW);
  delay(2);
  digitalWrite(BEEP_PIN, HIGH);
  delay(1000);
  tone(BEEP_PIN, 400, 500);
  delay(1000);
}

Overall, I’d say I like this buzzer. It works exactly as expected.

Perseid Meteor Shower? I might actually need an umbrella.

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Well. As I’ve done for most of my backyard astronomy life, I find myself at the big meteor shower of the summer, the Perseids, and as usual.. the weather prediction is for clouds.

Why… Why do I do astronomy in a light polluted, notoriously cloudy city?

According to the weather, it may clear up a bit in the 2am and 3am hours tonight, which is close enough to the peak time, that I might just give up a nights sleep over the hope.

I’d like to set up the barn door tracker, put the 40mm lens on the camera and aim it at the shower’s radiating point. With the tracker I think I can take 1 minute exposures (if I set my iso carefully) and maybe catch some meteor trails with a nice star field in the background.

The nice thing is with nice bright Jupiter up at that time, I know I’ll be able to use it to get a sharp focus.

This is something I can safely start running with my intervalometer and go inside and take a nap.. Or.. wait… it could just rain all over my camera… Ok, so no sleep for me.

Barn Door Tracker, upgrade and measurement.

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I spent a couple days fussing with the barn door tracker.

I built it according to the design, and off the bat it worked very well with my 40mm lens.

But… I wanted to use a much heavier lens, and a more demanding one.. 18-200mm at 200mm.

Ok so the first night out with it I was using probably a bad set up to do the polar alignment. The night with the 40mm lens all I did was use my iPhone compass and bubble level to line it up.. and it performed well. The night I tried the 200mm lens I used version 1 of my polar finder scope setup.

I got star trails, but that was ok, because that night I unexpectedly photographed comet in the field of view while photographing Jupiter.

So this set me off on 2 paths. One to improve the polar alignment setup, and 2 to completely analyse all the sources of error in the barn door tracker as a system, to see if it just can’t do 200mm. I talked to the designer, Peter Qun and he said, yeah.. 200mm is pushing it too hard.. it’s designed for wide angle lenses.

So I went ahead anyways to see if I could squeeze error out of the system. And there are many sources.. the camera is heavy with such a long lens, and the thing is 3D printed, so there could be flexing and twisting.. The gears are 3d printed, so definitely not perfectly round, nor probably having the hub in the center –my printer is great, but realistically…

So I got this idea, put registration targets on the axel and at the end of the moving hinge, make a 16 minute video, and use Blender object tracking and some python code I wrote to read out angles every 30th of a second…

According to that it was running slow.. like 8% slow as far as angle… Then I learned that the stepper used has different versions, with different internal gear ratios… Peter’s code uses a steps per revolution figure that’s based on some people in arduino land taking steppers apart that weren’t meeting spec, and they found that rather than having a 64:1 gear reduction, it was like 63 point some awful fraction.. leading to about 2038 steps per revolution… Since I had to by 5 steppers in the package, I took one of mine apart, counted teeth and found that oops… my version really is 64:1… so I should be using 2048 steps per rev.

Well I updated the code and remeasured, and I got the error down to 3%. Since I had a lot of data, I tried to come up with an overall correction factor for angle, tried that and it did not help…

Being industrious I thought, hey… Why am I trying to make an open loop system be accurate? How about closing the loop by attaching an accelerometer module to the hinge, and read out the actual angle in real time.

Click the photo to check out the magnetometer/accelerometer I used from Amazon, buying it will also support this blog.

Oh.. Oh.. I learned a lot about accelerometer modules… They are totally noisy… But with a lot of filtering it looked like, if I set the tracker up level (not polar aligned) it did a reasonable job of stepping to the right angle at the right time, but no better really than the open loop version. Plus, though I had the math right so that the I could calculate pitch angle from the accelerometer data, even if I tipped the tracker.. I find out that at extreme angles, (such as 43.1, my latitude), the calculation for pitch angle is not reliable. Sources say, it’s only really accurate for small deviation from level.

So scrap the accelerometer, that I still have superglued to my tracker…

But this experience with angles and tilting and measuring, made me realize, that using Blender.. though it may be very accurate in object tracking, is very susceptible to the angle between my camera, and the tracker.. they’d have to be perfectly square to each other to read an accurate angle.. so scrap that idea.

So I resigned to just use it with the 40mm lens — why not? and decided to do a little upgrade.

The way it’s designed, you take apart part of the tracker, manually turn the lead screw to screw the hinge fully closed, and then bolt it down.. Which is fine, you use it for an hour or two, and maybe decide to reset the thing, and manually close it to set it up again… But ever looking to make life convenient I went about adding a micro switch to the end of the hinge. And I wrote code that homes the tracker upon startup or pressing the reset button.

Click on the photo above if you want to buy the same microswitches I did on Amazon, and support my blog at the same time.

Surprisingly — That much is very repeatable… Just like a 3d printer, the code checks to see if it is already homed, if so, move it up from home a bit.. then at a relatively high speed step it down seeking the home position, then move it up just a tad so it’s just off home, and now step it down slowly to finally find a good home spot. Now there is a bit of a risk to this procedure… considering the microswitch holder and it’s pusher are 3d printed parts, if either of them break off in the processes, the tracker will probably self destruct as it crashes down never finding home. I could not think of a fail safe for this… The microswitch is normally open, you seek home until it just closes, a broken off switch will remain open.

but… Repeated measurements have it homing to the same spot within the accuracy of my ability to measure it with my calipers.

Next was to, forget Blender, and just let the system home, track for 4 minutes and stop.. allowing me to make measurements at the home position, and at the 4 minute mark, repeatedly. and also it displays how much it thought it moved the screw… After repeated measurements I get that I’m within .15mm of the desired displacement. I really can’t expect it to do any better than that. My caliper cost me about $20.. I could write a story about how measuring with a cheap digital caliper involves some guesswork.

In the final analysis… I’ll need a clear night, to do the real proof of how well it tracks.

Better Finder Scope Attachment for the Barn Door Tracker

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Well, I’ve designed solid mounts so that I can mount my red dot finder to my camera and to the barn door tracker. What was going wrong in the first version is that there was a lot of wobble in the mounts. My fault, because my design for the shoe for the finder was inherently wobbly. The current attempt is based on a design on thingiverse.com, for basically a type of dovetail rail that the finder scope can attach too. The finder comes with it attached to an adapter to a Synta style shoe. And there’s absolutely no problem with that, except in my setup.. Here is a link if you want to buy one:

As you can see, the finder itself is clamped on to a pedestal that then attaches in to a shoe on a telescope… In my case that pedestal is so high, it limits the positions I can angle my camera to. So on thingiverse.com is a rail meant for my particular tracker that would accept a similar type of finder scope. Not exactly mine, but I used it as a starting point for my design. I ended up with a rail I can bolt to my tracker, has a low profile, and then I can slide the finder on and off and there is no wobble.

Rail for Barn Door Tracker

I also melded that rail design to a hot shoe mount, printed that, and that fits nice and snug into my camera hot shoe also without wobble.

Rail with Hot Shoe Mount

So the idea, as I think I explained in another blog entry, is that since the finder has alt/az thumbscrews on it that are normally used to align it to a telescope, I couldn’t count on those screws never turning. So without a reference of what 0 alt/0 az is, I saw no way to align it to my barn door tracker. There’s nothing on the tracker with which to sight the north star, to correct the aim of the finder. So my theory goes.. if my hot shoe is square and level to my camera lens axis, I can put the finder onto the camera, align it to the camera while sighting a star in the exact center of the camera frame and then adjust the thumb screws on the finder to line it up– conveniently my camera displays the square central focus spot through the viewfinder so I can really get exact. Once the finder is lined up, I can move it to the barn door tracker, and do a polar alignment.

So that’s step 1 in eliminating star trails. The tracker has to be well aligned to the pole. And I have to wait, looking like a week, for clear skies to try it.