jbdiver

OLED displays

89 posts in this topic

Something else to try is a bypass cap over the supply rails -- noise spikes might cause confusion for Mr. OLED.

Edit: would suggest as close as possible to the pinheader on the display.

Edited by latigid on

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3.3v works! So that explains how in all my photographs it shows me using 3.3V's before. Awesome stuff, thanks latigidon

Edited by mongrol

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The problems with the OLEDs is most likely a power related problem.

The 3.3V Regulator (LD3985M33R) on the STM32F4 Discovery board only provides 3.0V (because of a BAT60 diode in series to the output) and can deliver only 150mA of current. And it has to power the whole STM32F4 board. So there are only <100mA left for external components like the OLEDs.

The Raystar datasheet mentions 60mA for 50% check board (whatever this means). With 2 OLEDs your are already at 120mA. There might be conditions where this will work. But it will not be very reliable!

Other OLEDs (especially white on black ones) probably need much more current then the tiny onboard regulator can deliver.

This is only a problem for OLEDs which need 3.3V to work. 5V OLEDs should not have a problem as long as your external power supply can deliver enough current.

 

 

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Just now, CJ55 said:

The Raystar datasheet mentions 60mA for 50% check board (whatever this means).

It probably means "50% checkerboard", i.e. every other segment is black.

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My original problem started by plugging 7.5v into the Core board basically frying it. Would the regulator I linked above stop this stupidity damaging it again? I can just see me doing this in a couple of years when I've forgotten more than 5v's breaks SEQ's/

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A voltage regulator like the 7805 needs an input voltage that is higher than the regulated output voltage. The 7805 needs an input voltage between 7V and 25V to output 5V.

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The 7805 will get pretty darn hot for anything above 9 Volts or so, so I would take a conservative approach here and keep the input voltage in that range.

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There are plenty of efficient switching 5V regulators out there.

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That's right, they are only a few bucks more and can save you a lot of headaches, e.g. if you are potentially using a variety of different wallwarts to power your MIDIbox...

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Great. The whole shebang happened because I plugged by 7.5v spider PSU which powers about 4 pieces of DIY gear into the SEQ. I'll put in a proper regulator to stop it happening again.

Thanks everyone for all the help you've given. You're all full of r0ck and awesome.

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I have the very same problem as jbdiver. Winstar white OLED set to 5V, only nonsense characters get displayed.

I understand that stabilising the supply rails will solve the problem, hence I have tried a 1000µF bypass capacitor (had this size lying around) but without success.

My SeqV4 is already powered by an external supply that provides 5V (to the STM32F4) and 12V (to the AOUT board) so I can easily use these for the OLEDs as well.

Is there a good way to harness the 5V line from the ext power supply and somehow stabilize it? I would like to avoid using a regulator on the 12V and dissipate the difference in heat. Similarly, I would like to avoid adding another supply voltage.

What would you guys recommend? Any help is greatly appreciated!

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That's odd.  Vishay OLEDs (the new ones at mouser) are just rebadged Raystar parts

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54 minutes ago, Altitude said:

That's odd.  Vishay OLEDs (the new ones at mouser) are just rebadged Raystar parts

Yep. I think in reality my power problem was so marginal it could've went either way. Originally my Raystars and Midas screens were working fine on 5v power and without any jumper switching until my mishap. It was only when I started fiddling around doing the repair that it all went wrong.

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10 hours ago, mongrol said:

UBEC DC/DC Step-Down (Buck) Converter - 5V @ 3A output

I'm using Vishay oled's though which didn't seem to have the same power tolerance issues as my previous Raystars and Midas oleds.

The sentence that concerns me a bit in the description is "The UBEC has built in filter capacitors on the input and output, but its a switching supply so its a little noisy compared to a linear regulator." It sounds as if I reach the same result with just adding filter capacitors to the switched power rail I already have. However, in my initial try that did not work, but maybe I should use different capacities.

I think I will do some tests over the weekend using the 12V line with an 7805, just to see if that solves the problem and how hot it gets. 

I still would prefer to use the 5V rail I already have installed so I guess I will also try different capacitors for filtering. Would something like this maybe also work: http://www.hobbytronics.co.uk/s7v7f5-5v-regulator ?

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Hi, 
In an other project I use Raystrar 4*20 oled display with f4discovery. At first it had similar strange behavior and the probelm was that the oled supplyed with 5V power while the driving data lines provides only about 3V high level due to the direct connection to the stm ports. The 3V is way below the datasheet specified input high level which is 0.9*VDD. My solution was to lower the 5V power to the oled by a diode, but somewhere a 22ohm resistor was suggested to the same problem. Hope this helps.

Norbim

Edited by norbim1
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8 hours ago, norbim1 said:

The 3V is way below the datasheet specified input high level which is 0.9*VDD. My solution was to lower the 5V power to the oled by a diode, but somewhere a 22ohm resistor was suggested to the same problem.

Great comment, norbim1! This may explain some random OLED misbehavior, which i also experience on my secondary MBSEQ... I always suspected my 5V switcher to be too noisy, but this makes total sense!
Karg: I'd recommend to try this out, in addition to your 5V linear regulator tests!

Also, for another project with a different OLED (256x64px, 16 blue levels), it helped for me to filter directly at the supply pins of the OLED, with a 100nf, 47uF pair... this should get rid of high frequency ripples.

Many greets and good luck!
Peter

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On 13 November 2016 at 7:30 PM, jarvis said:

FWIW - I would not recommend these white on black LCDs from buydisplay.com - the refresh rate is terrible and there is significant bleed from the backlight

I wish I saw this post a few weeks ago before ordering one! The contrast is dissapointing and the background is a dark blue.

The green on black ones I ordered ( which are not listed on the site, i had to email them) are much nicer, although I didnt test the refresh rate yet.

Edited by Smithy

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On 11/12/2016 at 6:32 PM, mongrol said:

@tk. Yep, these Oled's were perfect before I b0rked by discovery board. I'd forgotten about the 0x02 though... so...

  1. Uploaded boatloader_update app
  2. Set lcd_type 0x02
  3. Store
  4. Reset
  5. Looked back in my enclosure thread and checked my previous voltage for my oled's (it's clear it's 3.3v on the pic).

Both screens still won't work at the same time. I remember having a helluva time when building this first time around and somehow in my build thread I came up back to 5V and 0x02. However, every photo I look back it it's clearly set to 3.3v.

Time for more oxygen I think.

I am now having this exact problem - I too accidentally fried my Discovery board (the previous revision) and now the OLED displays do not work with the new Discovery board (the latest revision). I even tried replacement displays (Vishay from Mouser) with no success. I am back to using my old/slow LCD's from buydisplay.com

Is it possible that this is a compatibility issue with the current revision of Discovery boards?

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@jarvis can you test Norbim1's suggestion of lowering the 5V supply current with a diode? This may be the reason for the problem, the new boards might have slightly different specs, a few mV difference may cause the trouble, if it has been close to the datasheet specs before with the old board...

Many greets,
Peter

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I am still struggling to get my OLEDs to work properly.

Giving themtheir own power converter did not significantly change anything. The solution to lower the supply voltage only made it worse by making the displays flicker.

I then requested the datasheet of the OLEDs and when I got it (file attached), it seems the problem is the opposite: the data pins need to be supplied with 5V and will not work with 3.3V. Thus, I am getting a  SN74LVC245, to try converting them to 5V now...

 

56-2586_v1.pdf

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I don't see a need to drop the LCD voltage rail with a diode, unless you're using a DISCO board without any Core PCB ( @norbim1 ). All data should be supplied at the same level as the rail according to the jumper settings.

The overcurrent of the DISCO Vreg could be an issue as @CJ55 said.

Also the 74HC595 chip has a maximum voltage of +7V, was this replaced yet?

 

9 hours ago, jarvis said:

I am now having this exact problem - I too accidentally fried my Discovery board (the previous revision) and now the OLED displays do not work with the new Discovery board (the latest revision). I even tried replacement displays (Vishay from Mouser) with no success. I am back to using my old/slow LCD's from buydisplay.com

Is it possible that this is a compatibility issue with the current revision of Discovery boards?

 

 

@Karg same deal, there shouldn't be an issue with the data voltage level as the jumper settings take care of it, no?

 

Edited by latigid on

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Hi,

In the core module the voltage level setting is working well with the LCD data lines (D0-D7) which are going through the HC595. But there are the control lines (RS, RW, E) which are pulled high with resistors only and the STM32F407 PIN protection diodes allows pulling them up to only somewhere around 4V. I agree, that at the 3.3V jumper setting the OLED overdrives the DISCO vreg, so you should supply it with an external vreg. I just think its way simpler using just one diode at 5V setting, than an external vreg with 3.3V setting.

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Okay, 

I've just tested two of my white OLEDs (AL4002A model). They're a bit easier as both the data and power expect 3V, so everything is fine with the simple pullups. To check, I used both the M997C and D revs of the DISCO board. The current is ~50mA each so that was okay for at least a few minutes. Quite nice displays, maybe a good candidate for a bulk buy at some point :). Although, there is a faint whine from the charge pump -- do other displays make he same noise?

20170224_133646.thumb.jpg.d6c2a27d1db986

 

What's interesting is the controller is listed as KS0066 or Equivalent 8-bit 68xx-Series and there are no config jumpers, but all is well. I don't know if that's an error, or there's some internal magic going on, but lcd_type 0x02 is working fine.

Something else to consider is that OLEDs (and LCDs) normally expect a power down sequence to extend the life, rather than yanking out the power cord. I wonder if this could cause the displays to fail, but it really should be implemented at the controller level IMO.

 

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I switched from 5v to 3.3v and now they work fine :confused:

So, my experience is that the Raystar White OLEDs work(ed, before the power zap) at 5v with power provided through an external regulator (Murata 5v switcher external to the DISCO board), and that the Raystar/Vishay Yellow OLEDs work at 3v3 with no external regulator (straight off the DISCO board). This is very strange since they are both spec'd at 5v.

But hey, it's working–I'll take that. A responsive display is such an improvement to the user experience!

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