I want to collect data (both Humidity & Temperature) from 80 sensors. let's say I have 80 "DHT 11 Humidity & Temperature" sensors (for ex. in a warehouse) and one Arduino Uno R3 pack. It's clear that arduino has no so many pins to connect. I'm sorry that I don't know if it's possible. If so, what can I use to achieve this? Thank you all for your suggestions.
Analog multiplexers are one way, but they tend to have a significant resistance when on, and this could cause the protocol not to work.
For 80 channels you need 7 bits addressing. Say you have an 8-input multiplexer, then a 3-bit address indicates which of the 8 inputs is selected. Use 10 of these, all with the three address lines connected, and you have 10 outputs from 80 inputs. Next, use a 16-input multiplexer to select which of the 10 inputs you want to use. For this multiplexer you need 4 address lines. Together with the other 3 address lines you have 7 address lines, enough to select 1 of up to 128 sensors. But I repeat, this approach may not work if the multiplexer's resistance is too high.
A more robust (albeit more expensive) is to use analog switches to connect/disconnect each sensor. Analog switches (Analog Devices has a lot of them) have on-resistances down to < 1 ohm, so the sure should be OK for the application.
To control the long series of switches you could use a daisy chain of 74HC595 shift registers, which only requires a couple of I/Os on your controller, but gives you virtually unlimited outputs.