Can webusb connect a website to a Kmtronic Usb one relay device in a ChromeOs chromebox?

Question

Hi I am trying to give a website direct on/off control of a usb relay on a chrome os device. In the past I just used some terminal scripts to run on start-up on a ubuntu device but chrome os is giving me a hard time making this work.

Answer 1

Based on the sample Linux code it looks like these devices are using an FTDI USB serial chip and support a very simple set of commands to turn the relays on and off. The FTDI chips are supported by ChromeOS and so you can use the Web Serial API to control the device like this:

let port = navigator.serial.requestPort();
await port.open({ baudRate: 9600 });
let writer = port.writable.getWriter();
writer.write(new Uint8Array([0xff, 0x01, 0x01]);  // Turn relay on command.
await writer.close();
await port.close();

This is a very minimal example. You can improve this by passing a filter to requestPort() to select only the USB devices you want. You also don't need to request permission every time. You can call navigator.serial.getPorts() to get a list of ports that your site already has permission to access.

See https://web.dev/serial and https://wicg.github.io/serial for more information about how to use this API.