Automatic adjustment of the LED (QHY-174-GPS)

procyon12
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Re: Automatic adjustment of the LED (QHY-174-GPS)

#21

Post by procyon12 »

Hi Andy, all,

As you wrote, you are using a docking station. Could this be an issue? - did you also try a dedicated USB3 port and/or another machine?

Christian
andyho
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Re: Automatic adjustment of the LED (QHY-174-GPS)

#22

Post by andyho »

Hi Christian & all,

Thank you for that. The "USB3 ports" on my Dell docking station are running at USB2 speeds, which I verified this afternoon using CrystalDiskMark. The i5 computer docked to it has a warranty which expired in 2014, so the computer is really old! Must get a new one soon.

Still, there is the issue about SharpCap's default Start Position & End Position. In the QHY174M-GPS On-Line Technology Document (https://www.qhyccd.com/index.php?m=cont ... =30&id=190), there is a table named "16BIT 1920*1080 USBTRAFFIC=0." The table shows START POS(B) = 4190 and END POS(A) = 10930 for a range of exposures from 20ms to 500ms.

These calibration settings appear to be from QHYCCD's program "EzTimeStamp." But are they the correct settings for SharpCap?

Even if they are the correct settings, why does SharpCap interchange the two numbers so that SharpCap's default values are End Position = 4190 and Start Position = 10930 (or 10839 or something similar)?

In the paragraph titled "Calibration LED" of the On-Line Technology Document one reads: "You can adjust start time of this pulse and check the image, for shutter starting time, When you increase the pulse position and found [sic] the LED pulse from invisible to visible. This position is just the starting position. When you increase the position and found the LED pulse from visible to invisible. This is the ending position."

This indicates to me that End Position follows Start Position.

Robin mentioned some time ago that he has information, after corresponding with Dr. Qui, that End Position < Start Position. I wonder whether he could review that information again to make sure that something wasn't miscommunicated.

Andy Howell
Gainesville, FL
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Re: Automatic adjustment of the LED (QHY-174-GPS)

#23

Post by admin »

Hi,

I think QHY have the titles of their columns wrong on that web page - I have exactly the same data in an email from QHY with the column titles swapped around. I also received this diagram which shows how the start/end calibration represent a delay from the vsync pulse
temp4cj.png
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Capture.JPG
Capture.JPG (51.42 KiB) Viewed 1734 times
cheers,

Robin
andyho
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Re: Automatic adjustment of the LED (QHY-174-GPS)

#24

Post by andyho »

The sketch is fantastic! It nicely illustrates my example when SharpCap's nominal exposure = 1 second.

For the values given in the sketch, Exposure time = 2850-6280 < 0, which could not literally be true. I believe that 75,000,000 must be added to the result.

Is it an accepted fact that the number of ticks between vertical syncs = 75,000,000, and that the time interval between syncs is nominally 1 second?

On my system, End Position is observed (using the LED) at 75,107,060 and Start Position at 158,120. The difference is 74,948,940, which is 0.068% smaller than the expected value of 75,000,000.

Also on my system, the GPS Status window shows GPS exposure = 999,327.6 microseconds. This is 0.067% less than the expected value of 1,000,000 microseconds.

The computed results are in excellent agreement. A nominal 1 second exposure on my system is 999,327.6 microseconds, which is equivalent to 74,948,940 ticks. Percent deviation from nominal is -0.067% or -0.068%, depending on which metric (ticks or microseconds) is used.

My observations are consistent with the notion that End Position > Start Position. To find End Position, one must search in the neighborhood of Start Position + 75,000,000 * Exposure (seconds).

Start Position seems to be a strong function of several factors. On my system, the observed value = 158,120, which is quite different from SharpCap's predicted Start Position = 10,839.

I enjoy SharpCap and learning how to use it with the QHY174M-GPS camera.

Andy Howell
Gainesville, FL
procyon12
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Re: Automatic adjustment of the LED (QHY-174-GPS)

#25

Post by procyon12 »

Hi,

Just tested out of interest:

The current autocalibration (W7-64, USB 3.0, latest beta, full frame, 8 bit, traffic 0) gives exactly (except for exposure times < 7 ms) the table values.

Christian
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procyon12
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Re: Automatic adjustment of the LED (QHY-174-GPS)

#26

Post by procyon12 »

Hi,

I add the current autocal values for 16 bit, all others as above. There was always immediately lock.

With USB 2, the autocal results seem not to change, however, the framerate will be insufficient.

@Andy: It would be interesting if you get the same autocal results (regardless of the current ambiguities) - I think you should. If not, it would be a hint regarding possible basic issues e.g. with your system.

Christian
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Re: Automatic adjustment of the LED (QHY-174-GPS)

#27

Post by admin »

Hi,

just to re-iterate, adding the exposure time * 75,000,000 to the end pos is incorrect as far as we know. The camera firmware/software expects the end pos to be the smaller value, not the larger and can give interesting errors (including the GPS data freezing) if you use the larger value and set the value too high.

Robin
andyho
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Re: Automatic adjustment of the LED (QHY-174-GPS)

#28

Post by andyho »

Christian,

Using autocal on my computer is pointless, because of the "issues" (old computer, USB2 speeds, etc.)

My friend has a brand-new NUC computer that I am sure has all the up-to-date hardware. Here are the results she gets by manual calibration:

"Extra" (3rd) transition = 4219.
125ms: Start = 10910; End = 9382140
250ms: Start = 10910; End = 18757270
500ms: Start = 10910; End = 37507520
1000ms: Start = 10910; End = 75007200

What's interesting is that her "extra" (3rd) transition, which is an "End Exposure" transition, occurs at position 4219. This is close to your autocal End Position = 4190.

HYPOTHESIS:
3rd Transition = End of PREVIOUS exposure.

Relating this hypothesis to Robin's diagram, we make the following identifications:
3rd transition = Tend(0)
Start Exposure = TStart(1)
End Exposure = TEnd(1)

EXAMPLE: (my friend's data @1000ms):
Tend(0) = 4,219
TStart(1) = 10,910
TEnd(1) = 75,007,200

CONCLUSION:
Autocal must identify TEnd(1), not Tend(0), as the end of the exposure that begins at Start(1).
procyon12
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Re: Automatic adjustment of the LED (QHY-174-GPS)

#29

Post by procyon12 »

Hi,

W7-64, USB 3.0, 16 bit, 640x480, traffic 0, latest beta, 125 ms only tested: manual calibration.

Your NUC result for 125 ms:
125ms: Start = 10910; End = 9382140
My manual calibration result for 125 ms:

> StartPos:
LED ON>OFF = 10095 (roughly identical with autocal and NUC)

> EndPos:
First LED OFF>ON = 9382105 (roughly id. with NUC) Lock, plausible fits header times
Second LED OFF>ON = 4105 (roughly id. with autocal) Lock, plausible fits header times

So we have 1 StPos and 2 Endpos. Does it matter which end position is used?

Christian
andyho
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Re: Automatic adjustment of the LED (QHY-174-GPS)

#30

Post by andyho »

Christian,

Thank you for checking on your computer. IMHO, It makes a difference.

EndPos 9382105= Tend(1) is the one that, in principle, should be used.

EndPos 4105 = Tend(0) is the end of the previous exposure. Some people call it the "3rd transition" because they didn't understand what it was. Now, I believe that the 3rd transition is, in fact, the end of the previous exposure.

What is GPS Exp. (microseconds) that you get using EndPos = 9382105, and what do you get using EndPos = 4105?

(GPS Exp. is displayed in the GPS Status window.)

Andy Howell
Gainesville, FL
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