DLC cover jogs a bit every few seconds

[Arnold Wittstein]

Hello Nathan,
Thank you SO much for making this wonderful project available to the community. I'm in the process of making one now for my SharpStar150HNT2.8 before taking it to a remote observatory in New Mexico! It works amazingly well, except for one small thing that I have to work around at the moment. Whenever 12 volt power is connected, the servo motor "jogs" just a tiny bit, enough to move the cover only a few millimeters, every two seconds. This happens when it is both open and closed. It's not much, but the abrupt motion is enough to introduce vibration in the test images I've taken so far. What I am currently doing is using a Pegasus Astro Powerbox to apply power to the DLC, open the cover, then disconnect power. When I need to close the cover, I connect power again and close. It's certainly not a deal breaker, but it would be great if there was a way to correct this for the inevitable times when I forget to disconnect the 12v and don't realize it until the first blurry image comes in.
Thanks so much,
Arnie

[Nathan Woelfle]

Hi Arnold,

Thank you for taking the time to reach out to me with your issue, and thank you for the kind words. I am glad you found this project and can take advantage of it.

To make sure I understand correctly. You're using the Pegasus Astro Powerbox, which you've connected to the DLC, allowing you to turn on and off power to the DLC. However, the issue is when power is continuously supplied to the DLC, whether the panel is open or closed, the servo repeatedly jogs roughly every two seconds. Is that correct?

To verify, looking at the tech specs on the website, I assume you're using one of the four 12V ports with a 2.1mm center positive port and not the RCA connection, is that also correct?

For testing purposes, if you use a dedicated 12V power supply when power is applied to the DLC, does it twitch every few seconds? The Powerbox website states, "A powerful mosfet transistor provides "electric juice" to your precious equipment." My guess is the PWM power being applied is affecting either the LM1084IT-ADJ adjustable voltage regulator or the servo itself. The DLC also uses PWM and incorporates two capacitors to smooth out the signal to the panel, "eliminating" the "on/off" effect, which may be what's happening. If a dedicated 12V line stops the twitching, we may be able to solve this by adding in a couple of capacitors, similar to what I implemented. Let me know.

R/
Nathan

[Arnold Wittstein]

Hi Nathan,

Thanks so much for your quick and very thorough reply.

You are correct in both paragraphs 2 and 3 of your reply. In response to paragraph 4, today I powered the DLC with a dedicated 12VDC, 3A brick and the intermittent little jogs of the servo continued. Interestingly, they seemed to occur more on the order of roughly every five seconds, and it wasn't as consistent. The frequency varied between roughly two seconds up to five seconds at random. It may be my imagination, but the intensity of the jogs also seemed more variable, with the jogs occurring more frequently being a little less strong. Very weird.

I'll be interested in hearing what you think!

Arnie

[Nathan Woelfle]

Interesting. OK, so if the panel is still twitching, even with a dedicated power supply, my guess is it's the servo, but it could be something else. Doing a quick Google search, a common theme is the servo and Arduino need to be ground to the power supply. Did you follow the schematic and use the same parts? Can you check the voltage at the input power side of the servo and from the signal on pin 9?

[Arnold Wittstein]

Hi Nathan,
I've checked the wiring and I don't see any deviation from your schematic. I even made a second one from extra parts (the exact ones you specify in your parts list) and it is still happening. This is so bizarre! I also timed it more accurately and the servo does a tiny jog every six seconds.
After connecting to 12vdc and to the DLC application (which shows the cover as "closed" at start-up) I measure 10.5 volts between the pin that connects to the servo's positive pin and ground. At the same time, I measure 0.38 volts between the signal pin and ground. When I click the button to close the panel (not connected, of course, since the servo is disconnected to allow access to the 3-pin connector), the voltage between the signal pin and ground drops to 0.24 volts. It consistently swings between these two voltages every time I change states between "open" and "close" and back again. Does this help?
Thanks again,
Arnie

[Nathan Woelfle]

Arnie, that's good information and helps.

Let's start by addressing the power going to the servo. You stated the voltage is 10.5; however, this should be 6V. This may be where our issue lies, some servos can handle higher power than the specs list for higher torque and speed, but it's also possible the circuit has built-in protection, and maybe that's causing the jerking. So let's start there, getting the positive voltage into the servo down to 6V. Check that you don't have the 3.6k and 1k resistors swapped. Let me know when you have that figured out.

[Arnold Wittstein]

If only it could have been that easy! I have verified that the 1K resistor connects from the middle pin of the LM1084 (Vout) / positive lead of servo to the first pin of the LM1084 (labeled Adjust on the spec sheet, GND on your schematic) / 3.6K resistor, and that the 3.6K resistor connects from Adjust pin on the LM1084 / 1K resistor to ground. What's step #2?

[Nathan Woelfle]

Arnie, unfortunately, step #2 is still the same as step one; we need to get the voltage down to 6V. From what you've written, the resistors are in their respective locations, but you should be getting 6V, not a 10.5V output; this is very strange and what we need to solve. The second one you built, is the setup also the same and reading 10.5V? I'll work on putting together a test bench this weekend and see if I can duplicate the voltage you're getting to try to wrap my head around it.

In the meantime, can you provide your servo's make/model/SKU?

[Nathan Woelfle]

Hey Arnie,

I put a setup together, and it tested as expected, with an output of 6V. However, after adjusting the resistor locations, I got a 10V output. So I believe you have the 1k and 3.6k resistors on the wrong pin of the LM1084IT-ADJ. I have attached a picture showing the correct pinout. Please double-check this. If this does not solve the 6V output, please attach some photos so I can review what you have.

R/
Nathan

[Arnold Wittstein]

Well things just keep getting stranger. I just bread-boarded a quick circuit consisting of just a 12VDC/3A power brick, an LM1084IT-ADJ (from a different company) and the 1K and 3.6K resistors. I verified everything was hooked up properly both visually using your diagram and even measuring each resistor with a meter. Hooked up power and measured the output voltage. Six volts right on the dot! Hooked up everything else (but not the servo or Arduino yet) and measured the output voltage again. 10.5 volts!!!! I removed everything and re-measured the output voltage of just the bare-bones LM1084 and voltage divider - still 10.5 volts. Pulled that LM1084 out and put in a another one - 6 volts. Put the first one back in - 10.5 volts.
So something is happening when I hook up the rest of the circuit that seems to be affecting the LM1084. I have triple checked all the connections and everything seems right. I only have three more LM1084's left, so I can't afford to ruin many more of them.
The Pegasus Astro Powerboxv2 has a variable output port of 3 - 12 V at 3A. software-configurable. What about powering the servo from that and just leaving out the LM1084 and voltage divider?

[Arnold Wittstein]

Well, here's the latest in this confusing story.
I hooked up a 6V, 3A regulated power supply directly to the servo motor and the Arduino, leaving out the LM1084, voltage divider, 15 ohm resistor and Zener diode. Everything else is the same as your schematic. Verified 6 volts at the input to the servo. As soon as I apply power the little jogs every six seconds starts. When I connect to the Windows app, the little jogs continue in both the open and closed position. Tried two Arduinos and two servos, happens with all of them.
Any ideas?

[Nathan Woelfle]

You definitely have a conundrum on your hands.

Ok. Let's start with the last part first, the twitchy servos. Do you have the ground of the servo and Arduino attached to the ground of the power supply? If yes, and it's still twitching, let's take a further step back. You may have to add a couple more variables to adjust the pulse width of the servo. Can you hook up just the servo and Arduino like the picture attached and run the following code:

#include <Servo.h> 

Servo myservo; // create servo object to control a 180-degree servo 

void setup() { 
  myservo.attach(9);
 } 

void loop() {
  myservo.write(0); // tell servo to go to a particular angle
  delay(10000); // delay 10 seconds

  myservo.write(90);
  delay(10000); // delay 10 seconds
}

Does it still twitch? If yes, the change the myservo.attach with this

myservo.attach(9,600,2300); // (pin, min, max)

Does that work? If not try defining the.
min (optional): the pulse width, in microseconds, corresponding to the minimum (0 degree) angle on the servo (defaults to 544)
max (optional): the pulse width, in microseconds, corresponding to the maximum (180 degree) angle on the servo (defaults to 2400),
which may be listed on the servo tech specs.

Where did you purchase your servos from? Do you have a model #?

[Arnold Wittstein]

Hello Nathan,

Thanks again for your help with this. I tried the code below, and with
the modified myservo.attach(9,600,2300); line. Upon attaching power the
cover moved from its closed position to 90 degrees, then alternated
between 90 and 270 degrees (this is a 270 degree servo - I was unaware
of this when ordering it). The small jogs still happened, but less
frequently and seemingly random in pattern. Sometimes there would be no
jog during the ten second interval, sometimes one near the beginning of
the ten seconds, sometimes one just before the ten seconds were up,
sometimes as many as three within the ten seconds. I have not tried
changing the pulse width yet as I am not sure what to set them to (I
have electronics and Arduino experience but this is my first servo
project). If it easier just to order a 180 degree servo rather than
trying to make this one work, I am fine with that.

Sincerely,

Arnie

On 3/13/2023 4:50 PM, Nathan Woelfle wrote:

You definitely have a conundrum on your hands.

Ok. Let's start with the last part first, the twitchy servos. Do you
have the ground of the servo and Arduino attached to the ground of the
power supply? If yes, and it's still twitching, let's take a further
step back. You may have to add a couple more variables to adjust the
pulse width of the servo. Can you hook up just the servo and Arduino
like the picture attached and run the following code:

|#include<servo.h>Servomyservo;// create servo object to control a
180-degree servo voidsetup(){myservo.attach(9); }voidloop(){
myservo.write(0);// tell servo to go to a particular angle
delay(10000);// delay 10 seconds myservo.write(90); delay(10000);//
delay 10 seconds } |</servo.h>

Does it still twitch? If yes, the change the myservo.attach with this
myservo.attach(9,600,2300); // (pin, min, max)

Does that work? If not try adjusting
min (optional): the pulse width, in microseconds, corresponding to the
minimum (0 degree) angle on the servo (defaults to 544)
max (optional): the pulse width, in microseconds, corresponding to the
maximum (180 degree) angle on the servo (defaults to 2400)

Where did you purchase your servos from? Do you have a model #?

Attachments:

• tempsnip.png
  https://sourceforge.net/p/darklight-cover-calibrator/discussion/general/thread/401dff92ee/ba68/attachment/tempsnip.png
  (101.9 kB; image/png)

---

DLC cover jogs a bit every few seconds
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[Arnold Wittstein]

Would this one be appropriate?

https://www.amazon.com/dp/B073F92G2S/ref=sspa_dk_detail_1?psc=1&pd_rd_i=B073F92G2S&pd_rd_w=osweL&content-id=amzn1.sym.f734d1a2-0bf9-4a26-ad34-2e1b969a5a75&pf_rd_p=f734d1a2-0bf9-4a26-ad34-2e1b969a5a75&pf_rd_r=J8S1PMRJERFKVP22KRT8&pd_rd_wg=EsGP1&pd_rd_r=dc62b841-c41e-41dd-a7c7-afde3ac32fe0&s=wireless&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExSlA1Q0kxQlc5Tk40JmVuY3J5cHRlZElkPUEwNjE2NDg5MThBU0lFVzNSUTRBViZlbmNyeXB0ZWRBZElkPUEwMTkzODY4MzBJQldYR0JSRkQ4NiZ3aWRnZXROYW1lPXNwX2RldGFpbCZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

On 3/13/2023 4:50 PM, Nathan Woelfle wrote:

You definitely have a conundrum on your hands.

Ok. Let's start with the last part first, the twitchy servos. Do you
have the ground of the servo and Arduino attached to the ground of the
power supply? If yes, and it's still twitching, let's take a further
step back. You may have to add a couple more variables to adjust the
pulse width of the servo. Can you hook up just the servo and Arduino
like the picture attached and run the following code:

|#include<servo.h>Servomyservo;// create servo object to control a
180-degree servo voidsetup(){myservo.attach(9); }voidloop(){
myservo.write(0);// tell servo to go to a particular angle
delay(10000);// delay 10 seconds myservo.write(90); delay(10000);//
delay 10 seconds } |</servo.h>

Does it still twitch? If yes, the change the myservo.attach with this
myservo.attach(9,600,2300); // (pin, min, max)

Does that work? If not try adjusting
min (optional): the pulse width, in microseconds, corresponding to the
minimum (0 degree) angle on the servo (defaults to 544)
max (optional): the pulse width, in microseconds, corresponding to the
maximum (180 degree) angle on the servo (defaults to 2400)

Where did you purchase your servos from? Do you have a model #?

Attachments:

• tempsnip.png
  https://sourceforge.net/p/darklight-cover-calibrator/discussion/general/thread/401dff92ee/ba68/attachment/tempsnip.png
  (101.9 kB; image/png)

---

DLC cover jogs a bit every few seconds
https://sourceforge.net/p/darklight-cover-calibrator/discussion/general/thread/401dff92ee/?limit=250#ba68

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[Arnold Wittstein]

Thanks so much for continuing to work with me on this. I truly appreciate it.
The servo is a 20kg Do4.8-6.6V DS3218MG DSSERVO Digital Servo.
I have three, 12 hour, workdays in a row now so I probably won't be able to try your suggestions right away. I will be get them done ASAP and let you know the results.
Thanks again,
Arnie

[Nathan Woelfle]

For simplicity, yes, switching to a 180-degree servo would be much easier, but we can work with the 270. I leave the call in your hands. I recommend this one, https://www.amazon.com/ANNIMOS-Digital-Torque-Waterproof-Control/dp/B0769DFJVK/ref=sr_1_23?keywords=180+degree+servo&s=toys-and-games&sr=1-23, the working voltage is between 4.8 - 6.8V. The one you referenced looks OK but has a smaller working voltage space of 6 - 7.4V. Let me know what you decide, and we'll go from there. I hope you had fun with your shifts.

[Arnold Wittstein]

I'd much rather go with simple instead of trying to re-invent the wheel
with the wrong servo. My wife has Amazon Prime so we will have the motor
you recommended this weekend, I'll wire it up to the original circuit
and let you know what happens!

Arnie

On 3/17/2023 3:42 PM, Nathan Woelfle wrote:

For simplicity, yes, switching to a 180-degree servo would be much
easier, but we can work with the 270. I leave the call in your hands.
I recommend this one,
https://www.amazon.com/ANNIMOS-Digital-Torque-Waterproof-Control/dp/B0769DFJVK/ref=sr_1_23?keywords=180+degree+servo&s=toys-and-games&sr=1-23
https://www.amazon.com/ANNIMOS-Digital-Torque-Waterproof-Control/dp/B0769DFJVK/ref=sr_1_23?keywords=180+degree+servo&s=toys-and-games&sr=1-23,
the working voltage is between 4.8 - 6.8V. The one you referenced
looks OK but has a smaller working voltage space of 6 - 7.4V. Let me
know what you decide, and we'll go from there. I hope you had fun with
your shifts.

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[Nathan Woelfle]

Since you've had trouble getting the voltage to stay a consistent 6V, before you wire it up to the original circuit, let's ensure your voltage is correct first. I'd hate to see you fry a device. Run the basic tests to ensure it opens to the right positions without twitching; then, we'll diagnose your circuit. Let me know when you've got the new servo.

[Arnold Wittstein]

Success! Replacing the incorrect 270 degree servo with the correct 180 servo has solved the problem. Lesson learned - make sure you have the correct parts before starting. I hadn't even noticed this difference until you pointed it out. Thanks so much.
One question: the PegasusAstro Powerbox has a power port that puts out a regulated and reverse-polarity protected six volts at three amps. Do you see any problem using this to power the servo and the Arduino, thereby eliminating D3, D4, R10, IC2, R16 and R17?
Thanks,
Arnie

[Nathan Woelfle]

Arnie, that is excellent news! I'm glad it was a simple fix. I'm sorry if it was not apparent initially to use a 180-degree servo.

It is possible to use two separate power sources, a 6V for the Arduino and Servo and a 12V source for the EL Panel, but I recommend against it. Yes, you'll eliminate a few components, but then you'll also need to add a few others to ensure everything operates harmoniously and protects the components.

[Arnold Wittstein]

Hi Nathan,

I already have an 8" diameter flat panel that will easily attach to the
underside of the scope cover and already draws its power from the
PegasusAsto Powerbox. I am building the DLC without the light panel, so
I think I will power it separately off of the six volt output since I'm
not using that for anything else.

Thank you so much again for walking me through this. I truly appreciate it.

Less than a week and I get to install everything in a remote hosting
facility in New Mexico!

Arnie

On 3/19/2023 4:46 PM, Nathan Woelfle wrote:

Arnie, that is excellent news! I'm glad it was a simple fix. I'm sorry
if it was not apparent initially to use a 180-degree servo.

It is possible to use two separate power sources, a 6V for the Arduino
and Servo and a 12V source for the EL Panel, but I recommend against
it. Yes, you'll eliminate a few components, but then you'll also need
to add a few others to ensure everything operates harmoniously and
protects the components.

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[Nathan Woelfle]

Arnie, you are very welcome; it was my pleasure to assist. If you're building the light panel separately, you should have no issues with different power supplies. Have a fun, safe trip to NM.
I look forward to seeing pictures of your setup and work from NM.

R/
Nathan