about how many sensors we can connect to raspberry pi 3

[prahan gowda]

i want yo connect 2 soil moisture sensors and one humidity sensor and one 5v relay yo raspberry pi 3 is it possible bcz in board there is 5v 2 ports and 3v 2 ports are there.... soil moisture sensors hv 5v....and realy also 5v and humidity .3v .......m totally confused plz help me

[mfa298]

i want yo connect 2 soil moisture sensors and one humidity sensor and one 5v relay yo raspberry pi 3 is it possible bcz in board there is 5v 2 ports and 3v 2 ports are there.... soil moisture sensors hv 5v....and realy also 5v and humidity .3v .......m totally confused plz help me

It's going to depend on the sensors and distances.

The various 5v pins are connected together internally, same with 3v3 and gnd. So there's nothing to stop you splitting out the 5v pins to more devices. For experimentation some breadboard might be useful, you should probably then move that onto stripboard once you've got something that works.

For some sensors you might find if the wire is too long they don't work so well.

[wh7qq]

The simple approach to soil moisture is to connect the signal output to an analog comparator IC and use that output (hi or lo) to trigger a GPIO pin. Theoretically, you could use as many sensors as you have GPIO inputs on the RPi. You use a simple pot to adjust the moisture trip point. Long term stability due to electrolysis is your biggest problem but if you power the sensors briefly just several times/day to take readings, it would not be a big factor. See this tutorial (although Arduino based) for more info: https://learn.sparkfun.com/tutorials/so ... okup-guide

If you require analog results, you would have to use an A-D converter ahead of the RPi or use something like an Arduino with multiple A-D inputs...perhaps an easier solution but beyond the scope of this forum.