Digital Noise from OLED (now with examples) <- READ

So I had sent out a unit to a buyer and he was complaining about digital noise in the audio path. It was something I have not run into before so I built him a replacement. For testing units, I have a regular LCD with female headers that I can just pop in an out and the unit tested perfectly fine. Now when I attached the OLED, I can now duplicate the exact thing he describes (digital hash noise that is modulated by knob movements). I have a polarized 10 uF on the power pins of the display but that does NOT make any difference if I take it in and out…

Ideas?

Some OLEDs make this out of your PowerRail even when buffered with 100µ +

The only thing you can do is get another OLED and hope for the best…

Have you tried a ferrite between the Shruthi +5V and the OLED Vcc pin?

No, but that sounds like a good idea. can u post a link to an example? havent used them before

Just put it in series like a reverse Voltage protection Diode

something like this. pic is mouser link to the ones i have. i don’t know about what impedance would be best but mine don’t make problems in the power rails of my modules so far.
:http://de.mouser.com/ProductDetail/Fair-Rite/2743001112/?qs=%2Fha2pyFaduhAVm6lzZG4AwTJqeaw8N6jPEik2NB%2Fqv%2FUb%2b2PdI9ESQ%3D%3D

Hallo altitude

I think this is a problem of Step-Up-Converter in OLED Display. The best way is a seperate stepdown chip for the oled Display power.

See power-supply for my diy-synth: http://www.mutable-instruments.net/forum/discussion/2504/shruthi-synthesizer-and-my-wave-1/p1

Greetings Rolf

ferrite bead = RF inductor?

not sure how they call them, i’ve seen them as chokes also. it’s just a ferrite tube with a wire through

@altitude
Indeed it is.

Some of them look like slightly obese resistors (with colored stripes indicating inductance).

oh good, just happen to have a 10 uH one on hand, so just replace the jumper to the +5 on the display with the choke?

Which jumper?

the pin header, i. e. take out pin, replace with inductor

Yes, will work.

no dice, still there. I’m not sure what has changed, I’ve been using these (Newhaven) displays since the start and have never heard this before. You can hear it in the background a fair bit with the gate closed but when the gate is open, you can hear ALL sorts of crap in the audio

Your OLED is powered through pin 1 or through what is used for backlight on the LCDs?

I’m not sure what you’re asking (2:30 not a bit late for tech support?)

This is the pinout, i didn’t have 15 and 16 wired up at all

1: VSS
2: VDD
3: NC
4: RS
5: RW
6: E
7-14: DB0-DB7
15,16: NC

http://www.newhavendisplay.com/specs/NHD-0216KZW-AY5.pdf

Could this be a proximity thing? There is a big coil inductor on the back of this thing that sits a mm above the pins of the uC

@altitude Do you still have the capacitor in place? Maybe up it to a larger value. Also at audio frequencies the choke may not have enough dynamic impedance to filter off the hash-try using a 10 ohm resistor instead (you’ll get about a 0.5V voltage drop into the display but it should be able to handle it)

i dont think the cap is in play here, I tried cutting the leg to A/B the results and it makes no difference and that was with a 47 uF. I started with a 100 nF and worked my way up to 47 uF without any change in noise level so I am having serious doubts about this being a problem with power rail noise since I pulled the OLED off the board and replaced it with a normal LCD and the problem is gone…