Over the last couple of years I have been looking for an easy way to control a few relays from Javascript. I want to build a web App to control starting sequence horns for sailing races.
I recently discovered webUSB and it seems like exactly what I need. A direct connection from JS in chrome to the USB world. Simple coding in a language I already use.
On the hardware side I am having trouble finding a product that is compatible. Googling USB Relay finds 100's of products that all seem to rely on some proprietary SW for the OS. I can find lots of educational demo's that turn an LED on and off.
Does anyone have any ideas where to find such a product?
While I'm sure you will be able to find USB relays that can be controlled via WebUSB, most USB relays will probably come with some kind of serial port driver, e.g. https://numato.com/product/1-channel-usb-powered-relay-module uses a CDC serial port driver. These can be controlled using Web Serial, available in Chrome 77 and later behind a feature flag. For a tutorial, see https://codelabs.developers.google.com/codelabs/web-serial/
If you search for "5V USB Relay Programmable Computer Control For Smart Home" on eBay, you will also find low-cost relays that use HID instead. The advantage of these is that you don't need any serial port or USB drivers, as it will use the operating system's built-in HID drivers. For that you can use WebHID. For more info, see https://github.com/robatwilliams/awesome-webhid.