Hi, I just got quite enthused about the world of microelectronics, have got myseld a pi and couple of arduino uno boards to get started on my home automation project.
One question regarding the hooking up of sensors to a board, I see projects where several sensors are wired to 1 pin. For instance my light sensitive sensor, temp+humidity and PIR all would use the 5v and analog4 pins.
My question: is this doable without a breadboard of some sort by soldering the wires together, or making a dupont cable splitter, or is this not advisable?
Simple sensors that provide just high or low or an analog value need their own pin. Your PIR has a digital output and your photoresistor will be wired up as a voltage divider attached to an analog pin. Those two need a pin apiece.
There exist sensors that can share a pin because the sensors each have an identifier that lets the arduino request data for one in particular at a time. As AWOL mentioned, I2C and OneWire are protocols that such sensors use. An example is the DS18B20 temperature sensor.
Your DH11 sends a set of pulses specifying temperature and humidity but there's no addressing - it needs its own pin.
If you need an analog or digital pin, generally it doesn't matter which you use - if you have examples of code reading analog values for two different sensors but using the same pin, that pin selection isn't written in stone - you can move one of them and make the appropriate adjustments in your sketch.