I will be using a 9v 600mah battery to power the Arduino to the dc jack which I've been doing since forever. I will be using an Ir breakbeam that's compatible with either 3.3v or 5v , wired to pin 4 , 5v and ground. Sorry on my phone can't make a wiring diagram. The LoRa module I'll be using is a Reyax RYLR998 LoRa module that requires 3.3v . I've read forums saying yes you can connect to 3.3v and 5v at the same time but wanted to double check before I buy hardware. Also can someone explain how is that possible if Arduino needs those the power to run itself?
See level shifters and voltage dividers
You forgot to say what type of Arduino you are using. The answer can be very different for different types of Arduino. I will assume you mean Uno R3.
The Uno has 2 voltage regulators on-board, one for 5V and another fort 3.3V. Both can provide more current than the Uno needs for itself.
So, yes, you can draw current from both the 5V and 3.3V pin.
But I would not expect your 9V battery to last very long, certainly not "for ever" !
The UNO can only provide 50mA to the 3.3V pin, thats not enough for a LoRa module thats transmitting.
In addition the UNO uses 5V logic levels, and that LoRa device appears to use 3.3V logic so you cannot directly connect the IO pins.
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The 9V battery is a terrible choice to power your project. First, half your power will be wasted as heat. 2nd, the battery ampacity is too low and will only last minutes.
That unfortunately a mistake in the spec sheet that has been carried on from older boards, where the 3.3volt supply was stolen from the USB<>Serial chip. And is still true for the (classic) Nano.
The Uno has now a dedicated 150mA regulator (power stolen from the 5volt pin).
Nothing on the Uno draws current from that regulator.
I think that LoRa module draws 140mA in transmit mode.
Leo..
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