Can I send serial data from Snap! to a USB connected microcontroller

[cymplecy]

I've got the new RaspberryPi Pico and I just want to control the pins by simply sending micropython commands to it over its REPL

Just for proof of concept to switch the onboard LED off and on

[cymplecy]

I've got Node-RED sending stuff

but I'd like to do it from Snap!

[programmer_user]

Yes. Use the Serial API: קריאה וכתיבה מיציאה טורית  |  Capabilities  |  Chrome for Developers

[cymplecy]

I think that way beyond my pay grade to be the 1st person to implement that in Snap!
[edit
But I am making progress having enabled web-platform experimetal thing in my browser

[programmer_user]

const port = navigator.serial.requestPort();

You can't do this, the Serial API is asynchronous.
Here's how you would do it:

function encodeString(str) {
  const buffer = new Uint8Array(str.length);
  for (let i = 0; i < str.length; ++i) buffer[i] = str[i].charCodeAt(0);
  return buffer;
}
async function writeString(writer, str) {
  const buffer = encodeString(str);
  await writer.write(buffer);
}
(async () => {
  const port = await navigator.serial.requestPort();
  await port.open({ baudRate: 9600 });
  const writer = port.writable.getWriter();
  await writeString(writer, 'from machine import Pin');
})();

edit 2/13/2022: added quotes for the quoted code snippet

[cymplecy]

This is way beyond my JavaScript knowledge

[programmer_user]

There was a typo, try running the code now.

[cymplecy]

No error but what I need to do is send 3 strings one after each other so I tried this but my LED didn't light

[programmer_user]

I believe you need to add a newline (\r\n), but I'm not sure.

[cymplecy]

Your right - my NodeRED solution adds \r to each string
Tried it with this but is didn't make any difference

I think I'll need to replace the Pico with a Pi so I can see if any serial data is going out

[dardoro]

function encodeString(str) {
...
return buffer;

[cymplecy]

We have a LED on

[cymplecy]

Eureka - 1st block sets it up
2nd and third switch the LED on and off

Many thanks @programmer_user (and @dardoro for his crucial addition)

webSerial

[programmer_user]

How did I not notice that? Thanks, I've edited my post.

[programmer_user]

You should probably encapsulate the functionality into a block that sends Python code to the Pi.

[cymplecy]

yep - that's the ultimate plan
Block to select and open the port
Block to close it

Then parameterised blocks to setup and read and write to the pins.

[cymplecy]

I've hit a bit of a problem (presumably due to the async code)

If I try to wrap the opening function in a custom block - my browser just starts eating up memory and have have to kill it using task manager

Any ideas on how to get around this?

[programmer_user]

Where's your code?

[cymplecy]

I tried creating a simple custom command block to simply wrap the call block reporter

[toontalk]

In general I worry about using await in Snap! blocks. The reason it was designed to be asynchronous is that it might take a long time to work. While it is waiting nothing else can happen.

While more complex, I prefer passing in a command to the custom block (in this case the one that is opening a port) and calling it when the asynchronous function (navigator.serial.requestPort in this case) returns a value.