Plug the numpad into this computer with a USB-C data cable, then click Install and pick the serial port. Works in Chrome, Edge, or Opera over HTTPS.
After flashing, switch to the Customize tab, hit Connect, and Read from device.
After flashing, the device advertises as a Bluetooth keyboard (default name “Candy BLE”). Pair it from your phone/PC Bluetooth settings. Each key sends whatever you mapped. It deep-sleeps after the idle timeout and wakes when you press a key wired to GPIO0–GPIO5.