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I'm as new as you can be at Arduino programming and specific electronics, so I don't even know if I'm asking the correct question.

I've ordered an Arduino a breadboard and some PCBs and now I'm looking for a few parts that I should buy in order to get some basic projects done.

I'd like to start with a garden automation project, a fairly simple one. Humidity sensors, temperature sensors and a water pump.

Can I connect all (4) of the humidity sensors to a single local circuit and then connect that to the board so I can limit the number of input pins used? I'd still need to get independent readings from the sensors. Or would I need to use another board incorporating RF/Wireless/Bluetooth modules to receive the information and then send it to the board for further processing?

I'm sorry if what I just said makes no sense and I thank you for your time. All I have is low-mid level electronic related experience. Battery checkers, Power supplies, basic light sensors, PCB making ETC.

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    Jul 12, 2018 at 11:54

3 Answers 3

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If the connection is a digital sense pin then you can use a parallel-in serial-out IC to read them all simultaneously and then shift it in. Takes up 3 pins on the arduino a latch a clock and a data pin.

If the connection is SPI then you can connect the clocks and MISO pins together and then need a slave select for each. you can control many of them with a serial in parallel out IC or a decoder.

If the connection is with the I2C protocol and each device has a different address then you can simply connect them all in parallel.

If the sensor has an analog output then you can use an analog to digital converter (ADC) which can have multiple inputs and often have a serial interface.

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It all depends on the interface between the Arduino and the sensor.

For example the DS18B20 uses the 1-Wire bus. That requires one digital pin and a number of DS18B20 can be connected to the same 1-Wire bus. Every DS18B20 has an unique identifier that makes that possible.

Humidity sensors like DHT11 or DHT22 require a pin for each sensors. They are not accurate anyway.

Sensors like the BME280 use the I2C bus. The I2C bus allows that many sensors can be connected. Each I2C sensor has an I2C address. Sometimes a sensor can have just one I2C address and therefor only one of such a sensor can be connected to the I2C bus. But sometimes a trick is possible to have more.

This list goes on and on and on. A lot is possible without extra hardware.

Because you are going to use sensors and many sensors are 3.3V, did you buy a 3.3V Arduino board ?

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If you do not need them to run simultaneously, you can use a multiplexer such as this one from Sparkfun:

https://www.sparkfun.com/products/9056

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    This doesn't look like a question, it looks like an answer.
    – Nick Gammon ♦
    Sep 16, 2017 at 7:51

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