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I hooked up one of these LCDs

1.8 inch LCD

and noticed that the backlight flickers a lot when powered by the 5V from the GPIO port. The backlight uses ~100mA and the RPi was using just ~200mA.

The flickering is most noticable while booting, and persisted even when I powered the RPi from my bench supply.

Investigating further I unplugged the LCD and upon rebooting, noticed that the flickering also can be observed on the red power LED on the RPi.

The power LED is just connected by a resistor across the power supply, so this flickering represents glitches in the power supply.

Perhaps someone can catch the glitches on a DSO and post them up here.

Is it a good idea to add some extra capacitors? What type/value and where should they go?

  • If your power LED doesn't flicker during bootup, I would be interested to hear too. It may be that it's been fixed in the rev2 boards. – John La Rooy Mar 28 '13 at 4:10
  • ^ I'm guessing it was. – goldilocks Jan 13 '15 at 22:39
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When you say "and persisted even when I powered the RPi from my bench supply." were you using the same lead with the micro-USB connector on the end (I'm guessing the bench supply has some wires attached to the power pins of a USB socket that the lead is connected to?

If this is the case I would be suspicious of the quality of that lead - some USB cables have quite thin and skimpy wires inside and a poor production process may mean they are not bonded properly with the connectors on either end. The end result being a significant volt drop or even an intermittent connection across the lead which may well be made more obvious by flexing the lead whilst the RPi is powered.

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