Arduino Nano - How to add multiple sensors? Lithium battery requirements? LED requirements?

For the 5v pin: If you wire 2 sensors to the 5v pin, it will not effect sensor readings of either sensors, and should return separate sensor values regardless of whether or not they are both wired to the 5v pin.

In order to wire both sensors to 1 5v pin, without involving a breadboard you have 2 options:

1. wire both sensor pins, and the 5v pin onto a custom pin header PCB that connects 3 or more pin headers together
2. Strip 3 jumper wires and solder them together (2 for the sensors and 1 for the 5v pin)

For the lithium batteries: It says on their website: that the operating voltage is 5v, So your battery voltage needs to be at least that. It might be a good idea to get 2 (store.arduino.cc)

For the LEDs: If it is a standard LED, it should be able to withstand voltages of 3.3v or under. Thus the resistor is only absolutely essential for higher voltages. However, it is recommended to use a resistor even with voltages of 3.3v or below, because low resistance could shorten the lifespan of the LED

A multicolor LED as in an RGB LED?

To power and LED you will need current limiting resistors.

For an RGB LED you'll need 3, one each for the red, green, and blue channels. You'll need to do some math to figure out what resistance values you need. You need to know the supply voltage (5V) the voltage drop of the LED, and the current to supply to the LED.

Here is a link to an LED resistor calculator: https://ohmslawcalculator.com/led-resistor-calculator

The formula is R = (source_voltage - LED_voltage_drop) / LED_current

So if you have a 20 mA LED with a 1.3V voltage drop, and you are powering it from 5V (all fairly common values) you'd get:

(5-1.3)/0.02 = 185 Ω.

Then you would round up to the nearest resistor value.

You can safely use a higher resistance value than what you calculate. That will cause the LED to be dimmer. If you use a lower resistance you risk burning out the LED, or even burning out your Arduino.

For 20% resistors, that would be a 220Ω resistor. (The percent is a tolerance value. 20% resistors can have their actual resistance vary by as much as 20% from one to the next. You can get resistors in 20%, 10%, 5%, 2%, 1% tolerances, and even lower. The lower the tolerance value, the more they cost, and the more resistors you need to have all the possible values.

Don't use that value however. Look up the voltage drop and current for your LED and plug them into the above formula.

If you want to vary the apparent color of an RGB LED through software you can hook each color channel to a different PWM output pin on your Arduino. You then set each color channel to a different "duty cycle" to vary the brightness of that color.

This is an addition to the answer of Thomas Weller.

Also, I need to wire up a rechargeable lithium battery to both projects, I have a 3.7v 1000 Mah lithium battery and a charging port, but do I need more? Ive seen battery regulators, and other parts people recommend, but I want to make sure it will work with just those 2 parts.

I guess with "charging port" you simply mean a plug, where you can connect a power supply to charge the Li battery. Then the answer is: No, you cannot do it with only the battery and the plug. Lithium batteries are rechargeable, yes, but there is much to consider for charging. You must never ever overcharge the battery or discharge it beyond a certain point. Otherwise the battery gets broken (the result can be between simply holding less and less or no power, to the battery exploding).

Also you need to know the battery level to accurately charge or turn of the device, when the battery is empty. Lithium batteries mostly don't change their voltage enough between the full and empty states. Thus Li battery devices have a circuit, that measures, how much power is coming in (while recharging) and how much power is taken out (for powering a device), to determine the current battery level.

At your stage you cannot build that yourself, and also I wouldn't recommend that to anyone. You can by Li battery charger/regulator boards, which will do all that for you, and they are not expensive. There are also microcontroller boards, that incorporate that support for Li batteries.

Warning: unexperienced experiments even with low voltage may result in dangerous situations. E.g. a typical 10 Ohm resistor on 5 V may get so hot that it starts burning. Make yourself familiar with basic electronics, ideally with the help of someone else who can explain it to you. That person should especially explain the safety instructions first.

Both need to be plugged into the "5v" pin but there seems to be only one.

5 Volts means that this is a voltage source. In an ideal voltage source, you can basically plug in as many components as you like.

A real world voltage source will have a power limit. So you need to find datasheets of all components: the Arduino and the sensors. You can then read how much power the Arduino can provide and you can read how much power the sensors need.

As long as the Arduino can provide more power than the sensors need, that's ok. If it can't stuff will become more complicated, since you'll need another 5 V source and find a way to connect them safely.

Is there a way I could split the pins to add multiple sensors?

One does not split pins, one connects additional wires to a pin.

Will data be taken in simultaneously, and be cross compared with each other for code execution?

The 5V pin is only a voltage source. It will not provide or receive data. You'll need another pin or even multiple other pins to send and receive data.

Sometimes you can only have one device per pin (like a digital out pin), sometimes you can have multiple devices on a few pins (like I²C, SPI, 1Wire).

Typically, you would define what you need and then buy the components so you can build it. This requires a bit of knowledge, so watch some tutorials or introduction videos first.

I dont want to use breadboaard and want to wire directly to chip.

Sorry to be that direct, but at your level of understanding, that's probably not a good idea. Build it on a breadboard first and once it works as intended, make it a soldered circuit.

I need to wire up a rechargeable lithium battery to both projects, I have a 3.7v 1000 Mah lithium battery and a charging port, but do I need more?

As you said your components need 5 V, a 3.7 V battery will not help you at all.

You also need to be careful with the terms: a Mah is something totally different than a mAh. Don't confuse other people by mixing Mega (millions) with milli (1/1000).

Other than that, again, read the data sheets, find out how much current each component needs and sum it up. Then divide the 1000 mAh by the value you found, e.g. 100 mA and you'll get 10 h. That's how long it will last. Maybe it's good for your purpose, maybe not. How should we know that?

I want to make sure it will work with just those 2 parts.

That's great. Just consider all the aspects written in the data sheets of the components and it'll be fine.

I also need to wire a multicolor LED to the board, but do I need any resistors?

Yes. Read the data sheet of the multicolor LED and build a voltage dividor according to the values you find.

Totally new to EE

That's probably true. Maybe you want to start at the beginning and not jump into such a complex project. Get some resistors, measure voltages, measure currents. Make an LED light up. Learn about Ohms law, you'll need it very often. Once you got familiar with the basic stuff, come back to this project.

Honestly, I think you'll destroy components if you start with "a couple of projects".