Perpetual motion? The 128x64OLED that doesnt seem to need its Vcc.

Other Hardware Displays
1

So I've been tinkering with a variety of displays (TFT's, OLED's etc).

Today I tried out a 128x64 oled with an SSD1306 driver (good old ebay special). After the usual faff of installing the wiring, and finding a suitable library (adafruit) I had a little tinker. Bizarrely this display doesnt seem to need its Vcc line connected at all. Not only will it run without Vcc, it'll even start up without it! I guess it must be powering itself via the SPI connections....which just doesnt 'feel right'.

Has anyone else come across this? Is it normal behaviour for an OLED?

Connections for those who are into this:

Display Connection
1 GND GND
2 Vcc Not a damn thing! (was previously wired to a buck boost reg to give 3v3)
3 SCL Pro Mini 13 (SPI clock)
4 SDA Pro Mini 11 (MOSI)
5 RST Pro Mini 10 (Reset)
6 D/C Pro Mini 9 (DC)

Definitions in software:

#define OLED_DC 9
#define OLED_CS 0 // Display Im using doesnt have a CS!
#define OLED_CLK 13
#define OLED_MOSI 11
#define OLED_RESET 10
Adafruit_SSD1306 display(OLED_MOSI, OLED_CLK, OLED_DC, OLED_RESET, OLED_CS);

2

Incidentally, the claimed power benefits of OLED's dont seem to be that present. This thing burns ~13mA@3v3, which is much the same as a 1.8" 160x128 TFT.

3

I love these OLED displays, really cheap and easy to write to with the right library, had mine running in a matter of minutes. I cant comment on your everlasting gobstopper, but sure sounds a good way of saving power !! :wink:

Personally I like Sharps PNLC memory displays - you can write to them and remove the power and the LCD stays with the image (you only need power when writing to them !)

4

If you look at the datasheet for most integrated circuits you will find that you should never apply a voltage that is higher than the supply voltage to any of it's input pins, which is exactly what you are doing.

In your case you are powering the device via the internal protective circuitry on the I/O pins.

Don

5

Yeah thats kind of what i thought don. Dont panic, i prefer powering all peripherals via a regulator anyway, it just seemed an unusual behaviour. I'd have expected it not to work at all without a feed on Vcc :slight_smile: