Electromagnetic interferences on Alpha/Arduino?

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Andywaloo
Posts: 5
Joined: Fri Apr 02, 2021 3:49 pm

Fri Apr 02, 2021 4:23 pm

Hello,
I recently started using the Arduino on board my alpha instead of my former Uno... but it's a bit messy... components are tingling even without power. so I read the digital pins randomly getting high for no reason (with no program and nothing attached except a cable). In a project involving leds I was able to ghostly activate the leds just by getting my finger close to the data cable (connected to the Data pin of a 74HC595)... or when the mass of cables is closer to the alpha, in a much wider field... it's fun playing with for a while but what a mess... I suspect there are strong interferences... is it actually usable? Does it require turning off the wifi and bt (ah my mouse and kb)? removing the plastic cover? Your ideas are more than welcome!
As a side question are both systems properly isolated? or is there a risk that by burning the arduino I also burn the alpha board :o ?
Altogether, I'm considering buying a new arduino board...
Thank you in advance for your feedback
PS: I had attached two hdd on USB3, an hdmi monitor, a powered USB C extension with a 2.4 kb dongle and wifi and bt on.

User avatar
Andywaloo
Posts: 5
Joined: Fri Apr 02, 2021 3:49 pm

Mon Apr 05, 2021 8:50 am

Well I just ordered a new Arduino, I guess that kind of solves the problem and for just a few bucks :lol: ... I will use my alphapanda for what it does best, as a mini computer. I'm still curious though if anyone had the same issue or it's just me...

User avatar
ccs_hello
Posts: 745
Joined: Sat Oct 13, 2018 9:16 pm

Tue Apr 06, 2021 2:21 pm

Not sure it's EMI related or it's just insufficient decoupling.

I'd recommend place a low ESR 470uF 12V tantalum capacitor as well as
a low ESR 0.1uF 25V ceramic capacitor in between the
Arduino 5V and Gnd edge connector.
(Making sure the leads are as short as possible.)

User avatar
Andywaloo
Posts: 5
Joined: Fri Apr 02, 2021 3:49 pm

Fri Apr 09, 2021 12:34 pm

Thanks for your reply... can you elaborate? You mean right on the panda board, in parallel on a pair of 5V/Gnd sockets (attached picture)?

I measured a constant 900V/m near the panda... I'm not sure how precise the meter is, but as a reference the high speed (fiber optic) wifi router antennas were between 250 and 300V/m... my tablet 6V/m, my phone averaged 30V/m and peaked 100V/m with online gaming...
Attachments
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User avatar
ccs_hello
Posts: 745
Joined: Sat Oct 13, 2018 9:16 pm

Sat Apr 10, 2021 9:11 pm

Example of adding a 330uF 12V electrolytic capacitor (do follow the polarity, keep leads reasonably short.)
IMG_20210410.jpg
IMG_20210410.jpg (328.23 KiB) Viewed 942 times

User avatar
Andywaloo
Posts: 5
Joined: Fri Apr 02, 2021 3:49 pm

Sun Apr 11, 2021 3:23 am

Thanks, I only have smaller capacitors at hand (I'm stranded far from home), I will try for the sake of science and as a courtesy for your kind reply when I order capacitors for a project. But from what I see that fat capacitor with short leads would block both pairs... also the tingling I get from the strong electric field every time I'm close to the alpha is very uncomfortable so I would rather try to stay as far away from it as possible :roll: and my new Mega board is arriving soon...

Tips on reducing the strong electric field are welcome, I will experiment on my side and update here.

User avatar
Andywaloo
Posts: 5
Joined: Fri Apr 02, 2021 3:49 pm

Sun Apr 18, 2021 3:07 pm

After several experiments, nothing could reduce the electric field, even turning off the wifi. I guess when you have a tiny piece packed with electronics that's to be expected... Another issue with the Alpharduino is that you cannot turn it off. While working on a project with many components I melted a jumper head when connecting it to the 5V on the breadboard... All in all, better using a separate board! Thanks for your help CSS_hello anyway!

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