Enviro PHAT - Can it be cabled remotely from RPI?


#1

Two interrelated questions:

  1. Can the Enviro pHAT be connected to my RPI 3’s GPIO header via a 2-3m cable, or does it need to be directly attached to work correctly?

  2. Assuming it can be remotely cabled, I’m a tiny bit confused about the pin-out diagram shown on (for example) pinout.xyz – should I assume that that site is only showing the signaling pins, and that either 3.3v or 5v power and one of the ground pins are also used? How do I tell whether the pHAT needs 3.3v or 5v power?

Thanks!

-M.


#2

It can definitely be connected via a cable, but I’m not confident one that’s 2 to 3 meters long would work. At that sort of length various issues from external noise, to line capacitance could easily turn the i2c signals it uses to communicate into unrecognisable mush.

We (or rather mostly @RogueM) are working on adding the required 3.3v and 5v power pins to pinout.xyz, as it’s an oft-requested feature.

For now, though, Enviro pHAT needs only the 5V connection (it has an onboard 3.3v regulator) and I’d suggest connecting at least ground pins 6 and 25.


#3

Just as an FYI, I’ve extended the sensor via a (roughly) 2m cable (using 22AWG/8-conductor unshielded, stranded wire). Using 5 conductors for the sensor (using pins 2 and 14 from my RPI for 5VDC and GND, and pins 3,5, and 7 for the I2C signals), I’m getting essentially identical values back from the sensor compared to having it plugged directly onto the RPI header. The temperature value tends to rise after a while when plugged directly to the header, but is stable when extended via the cable.

I’m using the other three conductors in the cable for a PIR sensor (using pins 2,6, and 26 on the GPIO header). All seems to be working fine.

-M.