can i combine more than 4 input in arduino mega

hello everybody

im student from computer science departement

how can i combine 4 input as sensor in arduino mega???

its possible to combine RFID rc522, PIR sensor, Infrared Sensor and ultrasonic hcsr04??

You have to tell us what interfaces each of the sensors uses to connect to the Arduino. Post links to their datasheets

I would be very surprised if you can’t connect a lot more than 4.

…R

You can make them all work together smoothly if that's what you want. Your code can integrate the readings to arrive at meaning ("is someone there?" from combined data) as a task in itself, that leads to much smaller, cleaner, easier to debug, faster responding code.

Running processes in parallel without an OS to do it for us is one of the main lessons shown here.
Question as always is if the horse, once led to water, actually drinks.

In my signate space at the bottom of my post are 3 addresses to Nick Gammon tutorial blogs. All of his tutorials are complete and give common sense explanations with code and pictures, beyond what can fit on the forum.

Learning the first will get you started with making things happen on time without one task blocking others. His initial explanation involves making breakfast so that 3 items (eggs, bacon, coffee) are all done at the same time rather than each done before the next starts. Common sense. He shows and explains the code.

The second explores receiving serial data while allowing other tasks to run. Pay special attention to the State Machine part, it is a powerful tool to manage getting task code to run only the part needed to handle changing situations based on what has already happened.

With those two lessons you have the keys to write event-driven code without an OS. You should be able to make more than what you ask work on a chip with 2K RAM.

16MHz clock means 16000 cycles per millisecond. Don't lose sight of that. A LOT of processing can be done in less than 16000 cycles. OTOH it's very easy to waste many milliseconds with blocking code.