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Messages - BitBanger46

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OLEDs / Noise from on-board DC-DC converter
« on: July 23, 2014, 11:12:06 AM »
We are using an NHD 16-char x 2-line OLED display in a mixed signal application.  After 25 hours of troubleshooting, we discovered that the erratic behavior of the analog circuits on our board was being caused by a very strong 9.4 KHz ripple (90 mVDC) on the 5 volt (VCC) supply.  The ripple was so strong that it was transferred backwards through the 3-terminal 5 volt regulator on the board and onto the 12 volt supply!  When the OLED display was disconnected from the board, everything functioned perfectly.  We suspect that the root cause of the problem is the DC-DC converter on the OLED board which instantaneously draws significant current from the VCC supply.  (LED display boards do not have these on-board DC-DC converters.)

We were able to attenuate the ripple by bypassing VCC to ground with a 470 uF capacitor at the point where the VCC is applied to the OLED display.  However, the amplitude of the ripple is still sufficient to produce less than optimal results from the other circuitry on the board.

We checked the NHD data sheets but there is no mention of this problem.  We sent an inquiry to NHD describing the problem but have not received any response.

We will probably use the OLED display in some digital-only applications but we are going back to the trusty LED displays for any project that involves analog signals.

So, if you are experiencing the same kind of problem that we encountered, I suggest that you look at the VCC voltage with a scope and save yourself a lot of time!!

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