Situation : Yellow OLED display have a big inductor that sends a 13.5Khz sin wave in the preenfm2 audio path.
Yellow OLED solutionI spent some time trying to find a solution to this problem, and i have somthing really efficient.
Look at the After and Before screenshot.
If you have a PCB R5d (or +) : solder a 22ohm at the "oled" position and go to step 4 directly... DON't do step 1,2,3.If you have a PCB R5c (or -) : step 1,2 and 3 is for you.
The idea is to put a resistor 22 (ohm) between the LCD and the preenfm2 5V.
As there's no direct possibility, we'll use the Led+ pins (pin 15 of the LCD) that is not used with OLED display and where we can insert a resistor.
Step 1 : put a 22 ohm in the 68 ohm slot... this resistor is between the 5v and the pin 15 of the display.
Step 2 : cut the pin 2 of the OLED so that it's disconnected from the preenfm2 5V.
Step 3 : Link the pin 2 and 15 on the Display. Now the Oled is powered throught the 22 ohm resistor and get around 4v.
Step 1 to 3 makes the parasit frequency much more sensitive to shield. I think it removes almost totally the electronic noise but the magnetic noise is still there.
Step 4 : build a shield with many alumnium sheets that you use for food. you may have that in your kitchen.
The more you put the more efficient it is.
Take a 22cm x 22cm, fold 1 time then 2 times horizontaly, same thing vertically. You get 16 layers.
Do that with 4 sheets to get at least 64 layers.
Put that in a plastic bag (antistatic may not hurt) and add some tape. Be sure no aluminium will touch the contact.
Step 5 : put your shield under the screen.
Step 6 : Let me know
Xavier
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