How far can GPIO signals travel?

Question

I'm building a set of sensors for my greenhouse but don't want the Pi itself to sit in it. Instead I plan to build a custom PCB with connectors for my sensors and a cable that attaches to the Pi's header inside my house.

But how far can I expect the signals to be able to go?

Answer 1

The distance greatly depends on

1. cable quality (coaxial would be the best)
2. signal levels (5V are fine, but 15V or 20V would travel better)
3. signal frequency (1-2Hz can go very-very far, 1kHz might reach kilometers, 100kHz won't cross a football field)

You have to work out a compromise, depending on how far is your greenhouse and how much data you need to get. For once-a-minute temperature/humidity readings you'd be perfectly fine.