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OLED voltage levels...
alank2:
Hi Everyone,
Does anyone have any experience/knowledge about the many graphic oled's that are out there? I think they are SSD1306 based, and it seems like many are 3.3V, but I've seen some listings on eBay for 5V ones as well. I even saw an adafruit page talking about how newer ones were 5v tolerant, but I don't know if they were talking about their board or newer oled displays. Are they making newer models that can tolerate 5V?
Thanks,
Alan
zapta:
There are two main variations of the controllers, SD something and SH something (I will look it up later at home). They are very similar but have a shift in a pixel or two. The controllers are embedded in the glass,between the display and the flex cable. To know the operating voltage, check the datasheet of the controller and the schematic of PCB itself. Some like adafruit provide both an LDO and 3.3 <-> 5V level shifters, that's good. Other, claim to be 5V compatible but run the controller out spec, on the supply and/or the input pins. There are also different variations that look exactly the same but are different (different color, different controller, etc), with no model number and the seller don't always know what they sell It's quite messy when you buy from the Chinese sellers on ebay.
I get mine directly from Heltec so at least I know what to expect.
Hope it helps.
MarkF:
I have two of the Adafruit OLED displays. Their breakout board has a level shifter for 5V tolerant inputs. The 3.3V and 13V required by the OLED controller are both generated on the board from a 5V input. The SDD1351 controller is imbedded into the display cable (see attached pic). I've included the schematic of their breakout board.
alank2:
I got a noname oled off of eBay for a few bucks. Very tiny 0.49" 64x32. I didn't want to wait for a pcb to break out its 14 pin header I decided to try to adapt it to 100 mil pins for a breadboard by putting it on some generic proto board. I used thin wires from an ethernet cable that was stranded (each strand is pretty tiny). A true test of my soldering capabilities for sure. In the end I had all 14 pins soldered up and none of them shorting to each other. Other than one misunderstanding about the charge pump which I finally figured out, it is working great and I adapted my previous ssd1306 code from spi to i2c.
I have a couple of questions for anyone who knows more about OLED:
1. My understanding is that their lifetime for brightness is usually measured from 10K to 100K hours depending on the unit. I've heard this has to do with the display being powered up and that you can prolong life by shutting it down when not displaying anything. Since the brightness can be adjusted by changing the resistor on IREF, can you have a longer life by making the display less bright to begin with? The documentation mentions 12.5uA on IREF and another sheet I saw mentioned that one should not go higher, but if I went lower, say 8uA, will that extend life? Or will it just start dimmer and still get dimmer over time?
2. Some of the info I found on the charge pump shows using a higher voltage for it than the microcontroller voltage, such as 3.3V for the uC and 3.5-4.2V for the charge pump. Any idea why this is? The datasheet itself mentions vdd 1.65-3.3 and that should be <vbat and vbat 3.3-4.2). Does vdd have to be less than vbat? Why? I saw examples where someone was feeding the same 3.3v to both vdd and vbat.
It looks crisp and clear, but doesn't photograph well (at least with my camera anyway!):
Thanks,
Alan
Fungus:
--- Quote from: alank2 on September 21, 2015, 10:23:15 pm ---Hi Everyone,
Does anyone have any experience/knowledge about the many graphic oled's that are out there? I think they are SSD1306 based, and it seems like many are 3.3V, but I've seen some listings on eBay for 5V ones as well. I even saw an adafruit page talking about how newer ones were 5v tolerant, but I don't know if they were talking about their board or newer oled displays. Are they making newer models that can tolerate 5V?
--- End quote ---
You never can tell with eBay.
I know from experience that many are advertised as 5V but that only means they accept 5V power (they have an onboard 3.3V LDO for power).
The data signals still need to be level shifted 5V -> 3.3V though, or they simply refuse to work. I'm guessing they don't build level shifting resistors into the PCB because then it wouldn't work with 3.3V devices.
--- Quote from: MarkF on September 21, 2015, 11:19:04 pm ---I have two of the Adafruit OLED displays. Their breakout board has a level shifter for 5V tolerant inputs.
--- End quote ---
Yep, that one has a built-in 74HC4050 for level shifting. That will work with 5V data lines.
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