This project is a stationary linear barcode scanner made from an IR emitter and an IR detector. With the project deadline only weeks away, we decided to make a linear barcode scanner with photo-detectors instead. The operation of a photo-detector is very simple. Depending on the reflectance of the scanned object, photo-detector simply outputs different level of analog voltage (generally higher voltage for larger reflectance). Using the photo-sensitive nature of a photo-detector, we were able to construct a home-made linear barcode scanner at a very cheap price.
Source: Smith & Huang