Need some help powering OLED screen

Discussion in 'The Projects Forum' started by apollo, Oct 3, 2007.

  1. apollo

    Thread Starter New Member

    Oct 3, 2007
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    I bought a OLED screen and would like to power it up but I am not quite confident enough to attempt it without some help first since I'm new to electronics (only on page 215 of the first manual). Normally I wouldn’t even attempt it at this point, but since I already bought it, I want to make sure its not broken incase I have to exchange it for a new one (its quite expensive at $100). So can someone help me power it up, from there I can use the built in microSD card and software to test it with no additional hardware needed.

    Here is some brief info about the OLED screen: [​IMG]
    And here is a link to the docs on the OLED: http://www.4dsystems.com.au/downloads/micro-OLED/uOLED-160-GMD1/Docs/Pdf/ The pins I'm concerned with are the +, - and reset pins. The other two I don't need for now since I can run a script directly from the microSD card when the jumper is positioned correctly.

    I have built a basic 5 volt power supply onto a breadboard. It uses a 9 volt DC (500mA) wall transformer for its initial power. The schematics that I built it from can be viewed here: [​IMG]

    And it if I've interpreted the manual correctly, it says the OLED needs a nominal 5 volts power with 40mA of current, hence the reason I built the 5 volt power supply. But I'm not sure were to go from here to achieve the correct current without altering the voltage. By the way, I also have a push button for grounding the reset pin if that’s the way its done.

    Any help would be greatly appreciated.
    Thanks
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    The load will only draw as much current as it needs. Your 7805 is just fine as is. With only 40 ma, you might not have to add a heat sink to the regulator.
     
  3. apollo

    Thread Starter New Member

    Oct 3, 2007
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    Thanks for replying.

    So I can connect the positive and negative up with nothing in-between (like a resistor) and it will run the OLED at the correct current? I guess I need to do some more reading on why that is :)

    Why doesn't an LED work the same way? Is that because LED's need less voltage therefore needing a resistor, whereas the OLED works on the 5 volts I'm supplying it?

    Also I did put a heat sink on the 7805 just in case.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Your OLED's diodes have several layers of silicon junctions that the current must go through before it gets to the LED's themselves. Each junction drops approximately 0.6v - so, if the current had to pass through 4 junctions before the LED's, that would drop 2.4v, leaving 2.6v across the LEDs.

    LEDs by themselves are just an electrically bare junction - nothing "in the way" to limit the current besides the junction itself. Adding a resistor "throttles back" the current to protect the diode.

    A better scheme for diode protection is to use a current limiter circuit like a shunt regulator. That way, no matter what the supply voltage is (within the limits of the regulator) the proper current through the LED will be maintained.
     
  5. mrmeval

    Distinguished Member

    Jun 30, 2006
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  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Absolutely, the LM317 will work for that. It is somewhat overkill and large for this application, however.

    A TL430 or TL431 would both be able to supply more than twice the required current, with the added advantage of being "smoked" if there were a spike, rather than the OLED - and they're available in TO92 and smaller packages. Since the display is rather small already, having a small current regulator will be very convienient when it's time to package it.

    Both datasheets can be downloaded from either http://www.ti.com or http://www.alldatasheet.com
     
  7. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
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    For this project you won't need a current limiter. The OLED display needs 5V, and nothing more. An LM7805 to regulate voltage is enought, as beenthere suggested. The current will be as much as required by the display.

    Don't forget that the display has controlers and other digital circuitry built in, so besides not needed, regulating current would be a bad idea.
     
  8. apollo

    Thread Starter New Member

    Oct 3, 2007
    3
    0
    Thanks for the replies everyone.

    I powered it up as is and it appears to work good. With nothing loaded on the card I can only see the splash screen running, but that’s good enough for a basic test. I can't believe how sharp and vibrant the colors look on this OLED when compared to an LCD. Now I just have to figure out how to load some images onto the SD card using the software that I downloaded.

    Thanks again.
     
  9. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
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    A OLED screen has almost the same definition of a plasma screen, since it emits light instead of blocking it from a back light. Hence the black is much more intense.
     
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