Raspberry Pi 5v + 16x2 OLED
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Raspberry Pi 5v + 16x2 OLED

by spong3_ on Fri Feb 01, 2013 6:27 am

I'm trying to hook up a 16x2 OLED display to a Raspberry Pi,

http://www.adafruit.com/products/823

When I connect just the 1st and 2nd pins to the +5v and GND coming off the Pi's GPIO header, the Pi immediately resets, as if it had been shorted or too much current was drawing off it. However, the 50mA +3.3v pin works fine, and I can hook up the rest of the display straight to the GPIO pins and drive it with no problem.

Although the datasheet has the display at up to 30mA, I probably shouldn't be using the +3.3v pin for this(?).
Does the display have any known issues at 5v? Thanks.
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Re: Raspberry Pi 5v + 16x2 OLED

by adafruit_support_bill on Fri Feb 01, 2013 7:04 am

I did all my testing on these using 5v, so that shouldn't be a problem. How are you powering the Pi?
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Re: Raspberry Pi 5v + 16x2 OLED

by spong3_ on Fri Feb 01, 2013 7:10 am

adafruit_support wrote:I did all my testing on these using 5v, so that shouldn't be a problem. How are you powering the Pi?


I'm using a standard 1A USB mains power supply.
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Re: Raspberry Pi 5v + 16x2 OLED

by adafruit_support_bill on Fri Feb 01, 2013 7:51 am

That should be enough unless you have a lot of peripherals connected. But the display works fine at 3.3v, so it is not a short in the display. Maybe it creates some noise on the 5v rail that causes a reset?
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Re: Raspberry Pi 5v + 16x2 OLED

by spong3_ on Fri Feb 01, 2013 3:03 pm

Same problem with a different power supply, and when I bring the 5v rail down to 3.3v or 3.7v and try and use that, although the Pi no longer resets itself, the OLED display doesn't respond at all.

This is weird, any other suggestions please?
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Re: Raspberry Pi 5v + 16x2 OLED

by adafruit_support_bill on Fri Feb 01, 2013 3:39 pm

and when I bring the 5v rail down to 3.3v or 3.7v and try and use that

How are you doing that?
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Re: Raspberry Pi 5v + 16x2 OLED

by spong3_ on Fri Feb 01, 2013 3:43 pm

adafruit_support wrote:
and when I bring the 5v rail down to 3.3v or 3.7v and try and use that

How are you doing that?


A potential divider using two resistors (tested with a multimeter);
+5v => 10k resistor => 3.3v => 20k resistor => GND
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Re: Raspberry Pi 5v + 16x2 OLED

by Zener on Fri Feb 01, 2013 5:20 pm

There's a little problem with doing it that way... Did you verify the 3.3V while you were doing all that? Because it probably dropped out a lot. Quiz question is: what happens when you start to draw current through the 10k of the divider?
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Re: Raspberry Pi 5v + 16x2 OLED

by spong3_ on Fri Feb 01, 2013 6:05 pm

Zener wrote:There's a little problem with doing it that way... Did you verify the 3.3V while you were doing all that? Because it probably dropped out a lot. Quiz question is: what happens when you start to draw current through the 10k of the divider?


Do you mean read off the voltage in series while it's connected to the display?
I've tried it all the way up to 4.67v, still no luck. Although, when I send commands to it, it sometimes briefly flashes.
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Re: Raspberry Pi 5v + 16x2 OLED

by Zener on Fri Feb 01, 2013 6:24 pm

Hook a volt meter to teh 3.3V line and verify that it is still 3.3V with everything hooked up. I am guessing it is not.
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Re: Raspberry Pi 5v + 16x2 OLED

by spong3_ on Fri Feb 01, 2013 6:34 pm

Zener wrote:Hook a volt meter to teh 3.3V line and verify that it is still 3.3V with everything hooked up. I am guessing it is not.


You're absolutely right, it's dropping right down to 0.8v with the divider, but remains at 3.3v when hooked up to the working 3.3v line.
Thanks! Can you suggest a better way to lower the voltage please?
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Re: Raspberry Pi 5v + 16x2 OLED

by Zener on Fri Feb 01, 2013 7:23 pm

Put 3 diodes in series. That's not the best correct way but will work. Correct way is 3.3V regulator or bench supply.
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Re: Raspberry Pi 5v + 16x2 OLED

by spong3_ on Sat Feb 02, 2013 11:52 am

Zener wrote:Put 3 diodes in series. That's not the best correct way but will work. Correct way is 3.3V regulator or bench supply.


Tried again and with a 5v->3.3v regulator and it's working great, thanks! Looks like these things (or mine, at least) have an issue with 5v.
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Re: Raspberry Pi 5v + 16x2 OLED

by Static on Sat Feb 09, 2013 8:43 am

Glad I saw this. I'll be integrating a display into one of mine at some point.
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