RaspberryPi for imaging, USE A BATTERY! - Forums

Topic starter

Mar 12, 2021

Hi,

I don't have a question but just some info that might be interesting for folks that use the RaspberryPi (RPi) to capture images. Don't know if I'm telling common wisdom here but here it is:

I'm using a RPi4 to capture images with my dedicated mono camera. It also is doing the guiding. In my case, the mono camera is fan based and hence is fully powered through the RPi-USB port.
My advice: use a battery (with a 12V to 5V converter) as main power supply! Otherwise, you may see banding and other noise artifacts in your images!

Background: I had the RPi powered through a 230V to 5V USB power supply to capture darks and bias frames. At the scope, I am powering everything with a 12V lead battery. In post processing, I've detected noise bands and was surprised that I saw them but others on the internet didn't have it when people analyzed the amp glow pattern of the chip. After doing some experimenting, I identified that the power supply induced periodic noise. With a battery power supply I took again a set of darks and bias frames and everything was smooth.

Just in case somebody runs into the same issue.

CS!

Björn

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Rusty

Mar 12, 2021

Bjorn,

Interesting catch. I use a RPi4 as well with 120v from the house. I have noticed upon occasion some strange banding in my darks or flats. (not sure yet which). I will keep this in mind and try my 12v set up and hopefully catch any differences.

Thanks for the post,

Rusty

Björn Arnold

Topic starter

Mar 13, 2021

Hi Rusty,

One thing to keep in mind: my camera is completely powered through the RPi4 as it is fan cooled an hence can live with the USB power. If you are using a cooled camera, it will probably have a 12 Volt plug. So I cannot make any statement what happens then regarding banding but given my experience with the RPi4, I'd probably provide the 12 Volts also from a battery instead of a AC/DC converter.

Also my mount runs on battery, as I just don't trust the power supplies. We're talking about devices to turn a system by 15/3600 degrees each second.

Let me know what your finding are!

CS!

Björn

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Christian Großmann

Mar 14, 2021

Hi Guys,

I also use a Raspberry to control my equipment. I put everything onto my scope to have it set up all the time. I only have to put the power cable on to be ready to run in the fields. I use a 12V battery with 100 AH, which is quite oversized for my new setup. Between the battery and the equipment, there are some DC-Regulators that generate a 12V and two 5V power sources. The 12V powers a USB Hub, where nearly all the equipment is plugged into. The same 12V supply is used to power the cameras peltier element and the fan. The Raspberry is powered by one of the 5V lines. Here only a GPS Dongle is plugged in and of course the hub with the equipment. The secondary 5V line is used to power some relays and 2 DIY dew heaters. That all works really well for me.

If I work on the scope or when I create my darks, I use the scope with a power supply plugged into the 230V wallets. I never had any issues with that. But the difference may be, that the power supply is using a transformer to generate the adjustable output voltage. I set it to 13.7 Volts. This drives the Box with the DC regulators mentioned above. This is a two stage system.

Most of the "cheap" power supplies use capaciters to reduce the 120/230V voltage. This generates a lot of noise. Since the Raspberry didn't use any regulator for the 5 Volts, this noise may be given to the USB ports also. That's why I power everything from the hub. Maybe you can try another power supply that is using a transformer. Those are usually bigger than those small 5V cubes for phones etc. but generate a much more stable output.

Just a thought…

Greetings

Christian

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Björn Arnold

Topic starter

Mar 14, 2021

Hi Christian,

You're absolutely right. In the end it depends on the architecture and internal scaling of the power supply. For the darks, I had only the RPi connected to an Anker 230V/USB power supply. For whatever reason (insufficient filtering, resonant switching frequency) it creates enormous banding in the darks and bias frames.

The transformer solutions might be better. Maybe I'll give that a try - or build one on my own.

CS!

Björn

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