Maximum cable length of sensors


#1

What’s the maximum cable length that can be used to connect sensors? I read it’s only about 1m, is that right? I have a project idea for automating my home which means I’ll need to run cables up to 15m. How should I connect to sensors on the other side of my house?


#2

It depends on which sensors you’re trying to connect. But yes, most of them won’t be viable over 1 M. If you’re going to run sensors from one end of the house to the other, you probably need to consider either some sort of custom RF communications, or you need to consider using multiple GrovePi setups.


#3

Is that limitation only for the i2c connectors? Or for digital and analog also?


#4

For what it’s worth, I’m running over a single cat5e cable the digital temp+humidity sensor (pro) + i2c rgb display + i2c light sen sor. Cable is 5 meters long, works perfectly, error rate is very low.

But don’t count too much on that, I may be lucky!


#5

Hey Cedricm, that’s great it’s working. A few thoughts for anyone else interested in this sort of thing:

  • The analog sensors run at 5V. I would imagine even if you’re using some high quality wire, you’re still going to get some voltage drop across a very long piece of wire. So analog sensors will have a slightly lower than actual reading. Just a heads up here.
  • The digital sensors are a bit of hit or miss. Vast majority of the sensors in the Grove library are I2C, also operating at 5V. These too might be hit or miss, depending on the material of the wire, the length, etc. I think I read a while ago that I2C is really only good for communications over a few feet (again, becuase of voltage drop, but also because of a buildup of capacitance on the wire; a very long wire will begin to act like a capacitor and this will begin to degrade your digital signal).

Just some fun extra details, I’m glad it’s working!!


#6

I just connected a relais on D4 using a 20m telefon installation wire, and also the “blue” temp/humidity sensor DHT11 on D7.
It works weil, there are not more nan’ s than connected directy.
Shure, maybe not every sensor will work :slight_smile: