Two serial devices, one nano

Hi, I'm working on a small project where I need to plug an RTC module and an LCD with its i2c ointerface to a nano. I know it can be done on an uno, and that the nano is essentially a reduced version of the uno. What would be the pins to use?
I also be using a 4x4 numpad, a couple of leds and a relay. Can the nano power them all?

You need to power the relay directly from the power source, not from the controller.
Keyboard connects to the controller.

The Nano uses the same processor as the Uno so the same pins are used for I2C, SDA is pin A4 and SCL is pin A5.

I agree with Railroader the the relay coil may need an external power supply. It will also need a driver. Relay modules have a driver on board. What exact relay do you need?

How is the Arduino powered?

A keypad needs very little current so should not be a problem.

The LEDs may be OK as well, but since we do not know their specifications we cannot say for sure.

SDA and SCL on Arduino Nano are available on A4 and A5 pins. Look at the silk screen it should be labeled. There are a lot of various versions of the Nano and I do not know which version you have. Some of my nano's have extra pins labeled SDA and SCL but they are also wired to A4 and A5. As far as the keyboard yes but the interface determines how it is hooked up. I assume you are talking about 5MM leds or something in that size range operating at about 10mA, these would be fine. The nano actually has two additional A/D pins that the UNO does not (they are not pined out). Remember to connect all the grounds and use Pull Up resistors on SDA and SCL.

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