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  #901  
Old 27-05-2018, 12:15 AM
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luka
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No, we did not try the DC current to TEC. That would most likely work but we would have to control the DC current from the ATMega somehow. PWM was relatively easy and required no extra parts (I had to modify the board and swap pins as our current TEC pin does not support PWM).

Another option would be to smooth the PWM-ed MOSFET output and convert it to DC. Again extra parts and extra heat losses.

You should have some rest. Again, great to hear from you!!!
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  #902  
Old 27-05-2018, 07:04 AM
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wasyoungonce (Brendan)
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My first impression is induced noise from PWM. Yes Iíve see lots of efforts from other uses I think Garymack with smoothing.

Linear current control of a TECH is best done by bipolar transistor but I can run manual control via CC and CV modes using a PSU.

Might be a quick easy way to isolate. What you want is to half you problem doing this does that. The noise lines disappear or not.

I kinda get the impression you already know itís the PWM ... can you alter TEC frequency ( via at mega code firmware change). is there a change?

Jeez this is interesting getting my juices flowing but still stuck in hospital atm. Due out soon but that might not pan ou letís see Iím going to go read all the threads and try to get a handle. Can you point me to images of the issues with a link? Just makes it easy for me. Also Iím on mind bending drugs I spend a lot of time quite ďfoggyĒ which make it hard for me to comprehend. Forgive the typos again Iím using phone. I have my kappa and wifi modem so I have some luxuries
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  #903  
Old 27-05-2018, 07:06 AM
gehelem (Gilles)
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Nice to see you back Brendan, take care
Gilles.
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  #904  
Old 27-05-2018, 08:57 PM
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wasyoungonce (Brendan)
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Quote:
Originally Posted by gehelem View Post
Nice to see you back Brendan, take care
Gilles.
Gilles many thanks its been a tough ride! All I wanted was to get back to being half normal and play at the things I like ..like this projects!
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  #905  
Old 27-05-2018, 09:42 PM
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Brendan, here is a short summary of what is going on:
- The stripes are caused by PWM. The frequency of the stripes changes as the PWM changes. We went as high as 16KHz for the TEC switching frequency but short horizontal lines still formed a visible pattern in the images.
- The stripes are also caused by the cold finger left floating. Previous work with Canon 450D showed that the stripes go away once the cold finger is grounded.
- The back of our sensor is metal. However, unlike 450D and it cannot be grounded or the camera stops working.

So, there are two possible solutions:
1. Electrically connect the cold finger to the sensor.
2. Electrically insulate the cold finger from the sensor and then ground it.

For the option 1 we could not find any thermal paste that is electrically conductive. Most of them are designed for cooling CPUs and have good thermal conductivity but zero electrical conductivity.
Eventually Cedric (from the French forums) thought of using solder paste and it worked. Moreover, the camera read noise went down by about 15% as well.
However, I am not sure about the long term suitability of the solder paste.

Option 2 - I found a very thin (0.1mm thick) thermally conductive film that is also electrical insulator. I used it between the cold finger and the sensor, while also applying some Arctic Silver 5 (AS5) thermal paste on both sides. The thermal films and pads are usually used when the parts are pressed together by a large pressure and we don't have that - hence the use of AS5.
Then I could ground the cold finger without worrying that it may short the back of the sensor.
The preliminary results showed that this worked really well. I could not see the stripes at any switching frequency.
However, there will be a thermal loss because an extra interface between the sensor and the cold finger. I will need to measure this.
(Also I noticed an increase in the camera read noise but I swapped several capacitors at the same time which may be cause of this).
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  #906  
Old 30-06-2018, 06:30 AM
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Hi,

while waiting for some clear skies, I was thinking about the USB and power connections on my cam86: I think they share a common ground signal. Can this create a nasty ground loop, resulting in noise and other unwanted effects?

Nico
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  #907  
Old 30-06-2018, 11:58 AM
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Hi Nico,

Most of the switchmode power supplies are not grounded, i.e. the postive and negative DC outputs are floating. Just look at the mains connector of the power supply, most of them only have two pins for the AC and no pin for the earth.
So grounding one side of the power connector via the USB ground should not create a ground loop.


By the way, I have been too busy with work to do any more testing of the PWM TEC
Hopefully soon
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  #908  
Old 30-06-2018, 06:33 PM
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Hi Luka,

that should be the case, but I have noticed several times that if I touch the camera enclosure with the USB connector, then I can even see sparks meaning that the USB ground and the power supply ground are not at the same potential... I am powering the camera from a 12 V battery, and the USB is attached to a laptop running on its own battery. Did you notice anything similar?

And don't worry about the PWM TEC control: anyway I think the best option would be to redesign the board... but that is a whole other story!

Nico
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  #909  
Old 30-06-2018, 09:16 PM
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You have batteries and not power supplies... Is anything else connected to the batteries which is joining the grounds?

If not then what is happening is that the two batteries are not at the same ground potential as their grounds are not connected. Both are making 12V potential difference between their terminals but one battery relative to the other battery is not at the same potential. Likely also at a different potential to you, to the tree nearby etc. So when you touch the camera enclosure with the USB connector you basically connect the grounds together and a small current can flow over the air to equalise the two ground potentials. During this the electrons hit the air molecules and this produces light (a spark). The spark won't happen every time as the potential difference depends on the humidity, battery handling etc. Too small potential difference = no spark. As a rule of thumb, spark over 3mm gap corresponds to 1000V potential difference.

You will probably also see a spark if you just take a wire and join the two negative terminals of the batteries. Again a small current will flow to equalise the two ground potentials...
(just be careful connecting battery terminals, accidentally shorting the +ve and -ve terminals WILL HAVE BAD CONSEQUENCES as the (lead acid?) batteries can produce LOTS of current).

Anyway, there is still no ground loop as there is only one ground path from one battery to the other one:
battery 1 ground -> camera power ground (camera PCB ground) -> USB connector ground -> laptop ground -> battery 2 ground.

My setup is (still) in my backyard, powered from power supplies. I have never seen sparks but the connectors I used are "hiding" the wiring so it won't be easy to see sparks.
But I would not be surprised to see them when connecting the switchmode power supply (floating potential) to the laptop USB (another floating potential, the laptop mains plug has no ground).

Hope this helps (sorry about the long explanation, just looking for distractions from work )
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  #910  
Old 03-07-2018, 08:50 PM
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Hi Luka,

thanks for the explanation: still it is scary to see those sparks, especially when it's dark!
Hopefully I will have some more time to test the camera (here where I live it does not get fully dark until the beginning of August...)

Nico
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  #911  
Old 03-07-2018, 09:29 PM
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Beginning of August?
I may even find time to finish the PWM TEC control by then
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  #912  
Old 21-09-2018, 04:42 PM
Zoroastro (Luca)
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Good day all from Cologne to down-unter!

My name is Luca Mussati, I have read this forum for some time and now wanted to say thank you all - Luka great job with the software! - and ask if the cam86 is a stable/viable project. I bought cheap some D70 sensors and was trying hard to find reasons NOT to do this great project , besides having very little tools and no electronics knowledge of course

Since my son will help me on the latter issue I was looking for the latest IIS PCB Gerber files and BOM ... can you guys point me to the right place for that?

Thanks a lot!
Luca
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  #913  
Old 02-10-2018, 11:40 PM
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Hi Luca,

Sorry about the slow reply, I was dealing with some health issues but am on the way to recovery.

To answer your questions, cam86 is a viable project. You probably already know but the two other forums of interest are the original Ukrainian forum and the French forum.

The original project/PCB has not changed for quite some time so it is quite stable. Quite a few people are using it already.

Having said that, I have started working on improved cooling with PWM but run into some noise issues. I may have found a solution but could not test how well it works yet. If it works this would require a minor modification of the PCB (trivial compared to the PCB assembly). It would be easier to do on our IIS PCBs than on the original Ukrainian PCBs.

I'll send you link to our Google Drive folder with the BOM and Gerbers.

Please ask if you need any more info, I should be able to reply a bit faster now
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  #914  
Old 04-10-2018, 07:45 PM
N_DD
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Cooling

Hi,

I updated the ASCOM driver and camera firmware to the latest version, but I am now having troubles with the cooling: even if the software (APT) send a turn cooler on command, the cooler never actually gets turned on (see attached ASCOM log file). If I use the original hex and ASCOM driver provided by the Ukrainian, everything works.
Any idea why? I used to run the camera with the firmware 0.4 and ASCOM v0.73, but now, even if reinstall the same firmware and ASCOM driver, it does not want to turn the cooler on

Thanks,

Nico
Attached Files
File Type: txt ASCOM.cam86.1201.016120.txt (17.1 KB, 3 views)
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  #915  
Old 04-10-2018, 09:10 PM
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Nico, can you:
1. uninstall the driver

2. make sure that the folder
"C:\Program Files\Common Files\ASCOM\Camera\Cam86"
has been deleted.
(On 64-bit Windows it will be the folder
"C:\Program Files (x86)\Common Files\ASCOM\Camera\Cam86")
If the folder is still there can you let me know which files are in it before deleting it.

3. Reinstall the driver, update firmware etc.

On rare occasions the installer fails to clear files between the reinstallations so manually deleting the folder will give you a clean start (assuming ASCOM cleared options during the uninstall).
Let me know if it still does not work.

Which version started the problems? The latest (0.8.1) from the github with firmware 10?
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  #916  
Old 04-10-2018, 09:19 PM
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Important note:

After camera just has been switched on, during the first connection the software/driver may not set all the settings correctly. It was always doing this (since the original Ukrainian version) but I just figured out what was happening. No idea why yet.

The solution for now: After the camera has been powered on for the first time: connect, disconnect and re-connect again.

For example:
camera off -> camera on -> connect to camera -> possible PROBLEM -> disconnect from camera -> connect to camera -> NO PROBLEM

The following disconnections/reconnections are OK, it is only the very first time after the power was off where the issues may arise.
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  #917  
Old 04-10-2018, 10:43 PM
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Luka, thanks: I have tried to uninstall and reinstall the driver and re-flashing the firmware, but still it is not working.
However, I have realized that even with the original firmware the cooler get "stuck" at 1.56%, so I suspect I might have an issue either in the computer or in the power supply. I will try swapping them and let you know.

I am using the latest firmware and ASCOM driver from github. Before I was running the ASCOM driver v0.73 together with the firmware 0.4 and it did work.

Nico
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  #918  
Old 05-10-2018, 12:06 AM
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Definitely a power issue: using one with higher amperage solved the problem!

What I think was happening is that the TEC was drawing more current than the power supply was rated for (1 A) and that caused a "brown out" (low voltage). The voltage was still fine to power the camera logic, but somehow resulted in an erratic behavior.

So if you are running into weird problems, check your power supply amperage!

Nico
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  #919  
Old 05-10-2018, 12:08 AM
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Ah, don't you love the "weird" problems. What current/voltage is your TEC rated for?
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  #920  
Old 05-10-2018, 12:11 AM
N_DD
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...I love weird problems, but only if at the end I manage to solve them!!!

The TEC is rated at 3 A, so it was pretty demanding for a 1 A power supply...

I should maybe have realized before!
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