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Hi everyone,

I've have always connected 5V inputs to my Raspberry Pi through a voltage divider (2 resistors). But I'm now wondering why ? What is the precise reason ?

Is a circuit like "5V-->Resistor-->GPIO" safe ? If not, why ?

Thank you very much.

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I presume you are talking about 5v logic circuits. You could specify the value of the resistors.

The Pi GPIO would be damaged by connection to anything higher than 3.3v. A divider is one way of reducing voltage, but level shifter or clamp are more conventional (and better) solutions. For non-demanding (slow speed) applications this is OK.

PS If you were thinking of just connecting via a series resistor - DON"T. This may limit the current after it has damaged the input.

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  • Thank you for your answer. I just wonder WHY it's not possible to connect via series resistor ? What's the electrical reason ? Why isn't it working ? Thank you again.
    – armandkd
    Commented Mar 2, 2014 at 23:52
  • A resistor only drops the voltage when current is flowing. That current flow is what causes the damage. Putting a voltage above the 3.3v supply upsets the internal bias within the chip with unpredictable results.
    – Milliways
    Commented Mar 3, 2014 at 0:24

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