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Noise Filter

hsubdarb
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5 years 6 months ago #41672 by hsubdarb

Noise Filter was created by hsubdarb

I just purchased my first scope the Pico 2204a. I've been trying it out and finding it's perfectly adequate fory needs except for missing noise filtering. I was hoping just to purchase inline filters but I am not having any luck. I wouldn't mind building them myself but I don't know what combination of resistors and capacitors are needed. Anyone have experience with this?

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Matt T
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5 years 6 months ago #41685 by Matt T

Replied by Matt T on topic Noise Filter

Here's a link to the design tool I used when I threw a RC Low Pass Filter together. I just plugged in numbers for the resistors and caps I had on hand until I came up with a combination that looked like it might work.

sim.okawa-denshi.jp/en/CRlowkeisan.htm

This is what I ended up trying.

Before trace straight DC.

After with the Low Pass Filter.

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hsubdarb
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5 years 6 months ago #41708 by hsubdarb

Replied by hsubdarb on topic Noise Filter

I'm trying to figure out the balance between the resistor and the capacitor. Why did you choose that value for the resistor?

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Matt T
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5 years 6 months ago #41712 by Matt T

Replied by Matt T on topic Noise Filter

hsubdarb wrote: Why did you choose that value for the resistor?

I didn't want to go too high on the resistance, relative to the 1 meg impedance of my 'scope, because that would act as a voltage divider. Beyond that it was just a resistor I had on hand that looked like it'd work with the caps I had. Threw it together with alligator clips to see if it'd do what I wanted and it did. So at that point I just soldered them into one of the spare channels on the Hacktek 1008 :lol:

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hsubdarb
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5 years 6 months ago #41715 by hsubdarb

Replied by hsubdarb on topic Noise Filter

I was thinking lower resistance would be better. I'm looking at making an adjustable filter with a 1-100 ohm potentiometer.

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Matt T
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5 years 6 months ago #41716 by Matt T

Replied by Matt T on topic Noise Filter

hsubdarb wrote: I was thinking lower resistance would be better. I'm looking at making an adjustable filter with a 1-100 ohm potentiometer.

I like that idea of using a pot to make the filter adjustable.

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hsubdarb
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5 years 6 months ago #41721 by hsubdarb

Replied by hsubdarb on topic Noise Filter

I ordered all the parts. When complete I should have a fully adjustable filter from 1.5 hz to 72.3 khz. If I'm successful I'll post it here. This site has an easy calculator. www.learningaboutelectronics.com/Article...lculator.php#answer1

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hsubdarb
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5 years 6 months ago #41724 by hsubdarb

Replied by hsubdarb on topic Noise Filter

Could you please verify that the capacitor positive is tied to the circuit positive. I'm not having much luck finding a schematic that shows it.

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Andy.MacFadyen
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5 years 6 months ago - 5 years 6 months ago #41726 by Andy.MacFadyen

Replied by Andy.MacFadyen on topic Noise Filter

This was the hardware filter thread from the earlier days of the forum. Be careful with filters as they can hide too much detail. I don't know what the aquistion & sampling options are on your model of Pico but make sure peak detect is turned of and you should also have an averaging option which will supress at lot of the random noise.

www.scannerdanner.com/forum/diagnostic-t...lter-photos.html#376

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)

Last edit: 5 years 6 months ago by Andy.MacFadyen.

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Matt T
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5 years 6 months ago #41728 by Matt T

Replied by Matt T on topic Noise Filter

hsubdarb wrote: Could you please verify that the capacitor positive is tied to the circuit positive. I'm not having much luck finding a schematic that shows it.

I used a ceramic cap because they aren't polarity sensitive. If you use something that is polarity sensitive like an electrolytic strange things might happen if you connect to an AC or negative DC signal.

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hsubdarb
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5 years 6 months ago #41736 by hsubdarb

Replied by hsubdarb on topic Noise Filter

Okay. I'll find different caps.

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hsubdarb
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5 years 6 months ago #41745 by hsubdarb

Replied by hsubdarb on topic Noise Filter

Finding these caps is proving to be challenging. CBB61 metalized polypropylene film ceiling fan capacitors seem to be a good fit. I have a set picked out in the 450 volt range. This film type is recommended but I don't know if there is something with these that makes them a poor choice.

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hsubdarb
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5 years 6 months ago #41746 by hsubdarb

Replied by hsubdarb on topic Noise Filter

I will check it out. Thanks.

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