Check Scanner Demo

TypeScript SDK and demo app for scanning checks with a Digital Check CX35 scanner from the browser. The browser communicates directly with the scanner over USB/RNDIS via a Chrome extension — no native drivers or server-side components required.

scanner.mov

Prerequisites

• Digital Check CX35 scanner connected via USB
• Google Chrome
• Scanner configured with HTTP enabled and CORS set to * (one-time setup via scanner admin UI)

Quick start

cd web
npm install
npm start

Load the Chrome extension from extension/ via chrome://extensions (developer mode → Load unpacked).

Open http://localhost:3000 in Chrome.

How it works

The SDK runs entirely in the browser. A Chrome extension proxies HTTP requests to the scanner's embedded web server at http://192.168.2.1 (the scanner's fixed RNDIS IP). The extension is needed because browsers block cross-origin requests to local network devices.

Browser page
  └── SDK (window.postMessage)
        └── Chrome extension (service worker)
              └── fetch() → http://192.168.2.1/securelink
                                └── CX35 scanner (USB/RNDIS)

SDK usage

import { isExtensionAvailable, ScannerSession } from "./sdk";

if (await isExtensionAvailable()) {
  const session = new ScannerSession();
  await session.connect();
  await session.setParameters({
    fgsEnabled: "true",
    rgsEnabled: "true",
    MicrEnabled: "true",
  });

  const result = await session.scanOne();
  console.log(result?.micr.routingNumber, result?.micr.accountNumber);

  await session.disconnect();
}