Messages

1

Electronics / Re: larger CMOS sensor?

« on: June 10, 2019, 05:09:08 PM »

Hi Daniel,
Could you give the latest update about using  larger sensors ?
Thanks,
Stephan

2

Electronics / sensor Signal−to−Noise Ratio

« on: April 24, 2018, 06:18:13 PM »

Hi all

I was wondering whether someone ever characterized the noise of the sensor used on the miniscope, for example by measuring the Photon Transfer Curve (https://www.adimec.com/how-to-measure-the-photon-transfer-curve-for-ccd-or-cmos-cameras/).

Plotting the log of the  Standard Deviation versus the log of the average effective signal , one would expect to see a region where the photon shot noise is dominant, and the slope of the curve is equal to 0.5.

I measured this curve and identified a portion of the curve where the slope is 0.5 (STD~(MEAN)^(0.5)). This was roughly between the values 1 and 50 (at gain 4x). But to my surprise there is also another portion (much larger) which has a very different regime. In this portion, extending from the values 50 to ~200, I see the STD varying linearly with the MEAN.
Finally the curve ends as expected (values 200-255): the STD drops to zero as the pixels saturate.

I do not understand the linear relationship between STD and MEAN at the intermediate light levels.
Did anyone ever made this measurement? Did you observe the same thing?

Thanks for your help,
Stephan

3

Electronics / Re: larger CMOS sensor?

« on: March 08, 2017, 03:34:47 PM »

Hi Daniel,
I was wondering what is the latest update with your tests on alternative (and larger) sensors?
Thanks,
Stephan

4

Electronics / larger CMOS sensor?

« on: November 17, 2016, 07:35:59 PM »

Hi Daniel,
I was wondering whether you know of another CMOS sensor that could potentially be used (after redeveloping a new board of course) and having a ~square active surface, roughly twice as large as the current CMOS sensor.
Thanks,
Stephan

5

DAQ Software/Firmware / Re: dropped frames

« on: October 20, 2016, 09:35:10 PM »

Tested with a Dell Laptop running windows 10. It was the worst: 60 frames lost out of 1800.

So far, the best performing machine I tested was a recently purchased Dell Inspiron desktop equipped with a SSD drive: 1 to 4 frames lost out of 1800 acquired at 30fps.

I was originally using the DAQ 2.0. I just switched to the latest model, but that did not make a difference.

6

DAQ Software/Firmware / Re: dropped frames

« on: October 20, 2016, 05:57:39 PM »

Hi Daniel,

The sync output does indeed work well. And the issue seems to be related to the writing process.
I changed computer and now use a very recent one (Dell Inspiron, 3 months old) equipped with a SSD drive, and running windows 7.
I run a ~1800 frames movie at 30fps, and observed that the number of missing frames has been reduced by a lot, but unfortunately there are still some (4 in total). 

The writing speed has dropped a few times to 120fps, as indicated by the software.
As mentioned in my previous post, the counter of dropped frames remained at zero, although it should be at 4.
The time stamps data are showing when the problem occurred (calculating the difference between successive time stamps and plotting these values, you see peaks corresponding to the times one or few frames were lost).

Not sure what to try next because this machine is pretty good. Maybe try windows 10? I will check with a Windows 10 laptop, and let you know.

Stephan

PS: Here is the way I am measuring this effect:
In this set-up, no LED is connected to the CMOS board.
I have an arduino which is receiving the Sync output of the camera. The arduino is programmed to turn on a LED for ~10ms once every 2 rising edge of the Sync Signal (once every 4 frames). The LED is directed at the camera. That way, I can check whether and when a frame is lost looking at the movie (I should always see 3 dark frames followed by 1 bright one unless a frame has been lost).
The light of the LED is also reaching a photodiode. Its output, as well as the Sync Output are recorded on a NI-DAQ during the movie acquisition. This is used to make sure the Sync Output is fine and the LED indeed turned on properly.

7

DAQ Software/Firmware / dropped frames

« on: October 19, 2016, 09:53:46 PM »

Hi Daniel,

I observe dropped frames at regular intervals (when running at 60fps, there one or more dropped frames every ~75 frames as measured from the sync output; when running at 30fps, there are  several dropped frames every ~148 frames).
It comes at very regular intervals. Have you ever encounter that? Any idea what is going on?

Although there are definitely dropped frames, the software does not detect them and the "dropped frame counter" remains at zero.

Thanks,
Stephan

PS: in the current implementation I did not connected a LED to the camera board. I am running the system with an externally connected LED.