OLED voltage levels... - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: September 21, 2015, 10:23:15 pm
content: 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

author: zapta
author_rank: Super Contributor
timestamp: September 21, 2015, 10:32:10 pm
content: 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.

author: MarkF
author_rank: Super Contributor
timestamp: September 21, 2015, 11:19:04 pm
content: 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.

author: alank2
author_rank: Super Contributor
timestamp: October 02, 2015, 01:15:29 pm
content: 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

author: Fungus
author_rank: Super Contributor
timestamp: October 02, 2015, 01:43:19 pm
content: Quote from: alank2 on September 21, 2015, 10:23:15 pmYou 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 pmYep, that one has a built-in 74HC4050 for level shifting. That will work with 5V data lines.

author: Fungus
author_rank: Super Contributor
timestamp: October 02, 2015, 02:01:51 pm
content: Quote from: alank2 on October 02, 2015, 01:15:29 pmI'm not sure, but most of the dimming is caused by environmental humidity - moisture gets inside the polymers and is electrolysed. Lowering the voltage won't affect that very much.

author: amyk
author_rank: Super Contributor
timestamp: October 02, 2015, 02:39:50 pm
content: Quote from: alank2 on October 02, 2015, 01:15:29 pmAs a rough guideline, OLEDs are like regular LEDs in terms of current vs lifespan (i.e. the higher the current, the shorter they last), but more sensitive. Iref is only a reference current; the actual segment current at the output drivers is scaled up 8x (see page 26 of the datasheet) and 12.5uA reference current corresponds to 100uA driver current at maximum contrast (255). If you reduce that to 8uA then the maximum current will be 64uA.About the charge pump, make sure you get the right datasheet; some of the earlier revisions didn't have much info on it but I've attached revision 1.6, the newest one I could find, which specifies Vbat minimum 3.3V and maximum 4.2V (absolute maximum 5V) so powering it from 3.3V is fine too.

author: alank2
author_rank: Super Contributor
timestamp: October 02, 2015, 02:48:19 pm
content: Quote from: Fungus on October 02, 2015, 02:01:51 pmInteresting, is that moisture getting inside whether the unit is powered on or not?

author: Fungus
author_rank: Super Contributor
timestamp: October 02, 2015, 03:25:36 pm
content: Quote from: alank2 on October 02, 2015, 02:48:19 pmI guess so. The damage only happens when you switch it on though.A lot of the active research is in ways to seal them better/cheaper:http://gtri.gatech.edu/casestudy/improving-oled-lifetimes

author: alank2
author_rank: Super Contributor
timestamp: October 02, 2015, 03:39:15 pm
content: It sounds like better OLED's will be coming down the road.In this PDF:http://www.buydisplay.com/download/manual/ER-OLED0.49-1_Series_Datasheet.pdfIt shows a longer lifetime (page 7) at lesser brightness. Is there another way to adjust the brightness besides altering the iref resistor?

author: amyk
author_rank: Super Contributor
timestamp: October 02, 2015, 03:41:18 pm
content: Turn down the contrast (command 81h)

author: alank2
author_rank: Super Contributor
timestamp: October 02, 2015, 04:03:06 pm
content: Thanks amyk, what is the difference between adjusting the iref resistor or contrast? I've tried turning the contrast down quite a bit and it didn't seem to make a difference, maybe I need to turn it down more.

author: alank2
author_rank: Super Contributor
timestamp: October 02, 2015, 04:10:15 pm
content: Ok, I can see that a level of 0x00 is dimmer, bright still fine to look at, certainly plenty visible. 0xff is brighter, but I wouldn't call it intensely so.

author: alank2
author_rank: Super Contributor
timestamp: October 02, 2015, 05:40:23 pm
content: I made it step from 0x00, to 0x8F, to 0xFF, but I only see two brightness steps and only see two distinct steps when monitoring current.Could I have something connected wrong? I originally had pin 14 mistakenly connected to vcc directly, but fixed that. Perhaps it was damaged from that.Code:1c2pconnected to 2 via 1uf cap2c2nconnected to 1 via 1uf cap3c1pconnected to 4 via 1uf cap4c1nconnected to 3 via 1uf cap5vbatconnected to vcc (3.3v), line has 4.7uF cap to ground6vbref7vssground8vddconnected to vcc (3.3v), line has 4.7uF cap to ground9res#to uc10sclto uc, 2k pullup to vcc11sdato uc, 2k pullup to vcc12iref1M to ground13vcomh4.7uF to ground14vcc4.7uF to ground

author: Fungus
author_rank: Super Contributor
timestamp: October 02, 2015, 06:26:21 pm
content: Quote from: alank2 on October 02, 2015, 05:40:23 pmI dunno, but it's perfectly possible that that's the correct behavior.In the datasheet they mention three different brightness levels, FWIW.

author: alank2
author_rank: Super Contributor
timestamp: October 02, 2015, 06:39:10 pm
content: Quote from: Fungus on October 02, 2015, 06:26:21 pmI missed that which datasheet and where? I've seen something about 256 levels in a few sheets.

author: alank2
author_rank: Super Contributor
timestamp: October 02, 2015, 07:10:51 pm
content: It is working now. I tried a loop with all 256 steps and it kept increasing smoothly until rolling over and then I tried 8 steps from low to high and you can see each of those steps too. Pretty cool little displays to play with. I love that they emit light like a LED, but with fairly low power consumption.

author: Fungus
author_rank: Super Contributor
timestamp: October 03, 2015, 11:26:39 am
content: Quote from: alank2 on October 02, 2015, 06:39:10 pmThe one you posted, page 7:http://www.buydisplay.com/download/manual/ER-OLED0.49-1_Series_Datasheet.pdfQuote from: alank2 on October 02, 2015, 06:39:10 pm256 possible values in a register doesn't always mean they use all 8 the bits in hardware. eg They might only use 2 of them.

author: amyk
author_rank: Super Contributor
timestamp: October 03, 2015, 01:55:27 pm
content: Those are just a sample of the lifetime vs contrast graph. The controller has true 256-level gradation.

author: Fungus
author_rank: Super Contributor
timestamp: October 03, 2015, 04:50:40 pm
content: Quote from: amyk on October 03, 2015, 01:55:27 pmApparently so.But when I wrote the original post the OP was saying: "I made it step from 0x00, to 0x8F, to 0xFF, but I only see two brightness steps and only see two distinct steps when monitoring current."

author: alank2
author_rank: Super Contributor
timestamp: October 03, 2015, 05:44:58 pm
content: Quote from: Fungus on October 03, 2015, 04:50:40 pmI must have done something wrong for that, not sure why. It is working now and definitely has the 256 steps.I guess the question is, does using the contrast setting OR adjust the iref resistor both accomplish roughly the same thing?

author: amyk
author_rank: Super Contributor
timestamp: March 26, 2016, 02:48:22 pm
content: Quote from: alank2 on October 03, 2015, 05:44:58 pmIref is the "master contrast", it sets the maximum current. The contrast setting divides that into 256 steps.

author: reetpetite
author_rank: Newbie
timestamp: February 07, 2019, 12:06:41 am
content: Hello alank2 and all other contributors,I bought the same displays and I am struggling to connect them properly. What do you mean by “uc” on pins 9, 10, and 11?Best regards

author: alank2
author_rank: Super Contributor
timestamp: February 07, 2019, 12:12:01 am
content: By uc I mean microcontroller. Those pins need to go to a general purpose I/O to reset it and the other two to the i2c interface on the microcontroller. Good luck!