1

3 days ago I bought my first Raspberry Pi and it's a rev.B. I read that it provides through GPIO pins either 3,3V or 5V and the GPIO pins can handle between 2mA and 16mA each one. Moreover, to avoid an high impedance state (floating), the system is built with an internal pull-up/down circuitry that can be enabled via c/py/whatelse code.

My need was to mount a push button on GPIO30 (by using 3,3V) thus I soldered 8 pins on header P5 and I built a pull-up system with 10kΩ and 1kΩ resistors. It was done before I read the raspberry pi integrate a pull-up/down circuit...

My question is: It is necessary to build external circuits in order to avoid floating states? Could not be sufficient to rely on the internal p-up/down? Maybe it's a good practice to avoid the high impedance state during the boot phase..(?!)..

2

Internal pull-up and pull-down resistors are weak (they are something like 50-100 kOhm; I believe it's not specified exasctly). This may be to much in some cases. Also, as you sugested, pull-up/pull-down resistors configuration won't be persistant after boot so if your circuit depends on fixed configuration all the time, it's better to use external resistors.

  • It means that apart from inconsistency after boot, it is NOT mandatory but it depends on how much current is needed for specific applications. Now it's more clear, thank you. – Emanuele Dec 26 '13 at 14:43
  • You know, if it was mandatory to use external resistor, having internal one would be pointless :) – Krzysztof Adamski Dec 26 '13 at 19:23

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