PcompW7 — J's tudio

Nov 4, 2025

Week7: Lab: Intro to Asynchronous Serial Communications

Serial means that the two computers communicating are doing so one bit at a time, by sending pulses of data back and forth. Asynchronous means that the two computers that are communicating are each keeping track of time independently.

Week7: Lab: Serial Input to P5.js using WebSerial

I learned what is the asynchronous communications.

but my question is: why serial monitor that I created in p5.js cannot update real-time value of my potentiameter? Is that I did something wrong?

-Nov 13,2025 update

I went to Tom, and ask him about this issue. It turns out on my SerialEvent, I use read instead of readLine to read the value from the potentiameter. But my Arduino sends data one line at a time, so p5 needs to read it one line at a time. readLine() gives me a complete piece of data, while read() only returns a single character and breaks everything apart.

What Arduino Really Sends


In my Arduino code, I print sensor values like this:


Serial.println(sensorValue);


println() doesn’t just send the number. It sends

Each digit of the number

And then a newline character
So if the value is “123”, then it will send like:

'49' '50' '51'


It travels across the wire as a sequence of bytes.

But logically, 
Arduino is sending one complete reading per line.



What readLine() Does

In p5.js:

inData = serial.readLine();

readLine() patiently waits until it reaches the newline character
and then hands me the entire reading as a single string:

"123"

Once I realized this, 
the whole data flow felt almost elegan