Image Scan using Phototransistor Array
Well we have been using many electronic devices in our day to day life. All patented and commercialized. But making them on our own or bringing into light some innovation is totally an adventure which fetches in deep practical insights. Learning things and implementing them are two different aspects of understanding electronics. Here is one such implementation called image scanner which is made of an array of phototransistors. An array of transistors is used to detect intensity of light which is then transmitted to MATLAB for processing.
The idea behind designing this system was to exploit the use of phototransistor in scanning the object over a X-Y plotter. The X-Y plotter system is combination of mechanical and electrical design. In the assembly, we have 2 parallel metal threaded rods mounted onto a wooden platform using wooden blocks with holes drilled into them. Another vertical rod is mounted perpendicular to the two horizontal rods to facilitate a scan in all orientations. The PCB board with the phototransistor array is mounted on the vertical rod. Three stepper motors, two horizontal motors and one vertical motor, are used to drive the X-Y plotter. The movement of these motors is controlled using microcontroller ATMega644 and driven by motor driver ULN2003. For this scanner, light reaching the object is reflected from the image it is scanning. All the voltage signals generated by the phototransistor array is captured using ATMega644 A/D converter and then transmitted to MATLAB interface. The image scanner uses MATLAB as a software tool to process the scanned data and hence generate a bitmap image. This image is then stored as a .jpg file. Initially, the scanner is started by a calling function in MATLAB interface. The command is transmitted to the microcontroller by serial connection.
The photosensitive array used here consists of eight PS5022 phototransistors. Scanning speed of the plotter is directly proportional to the number of transistors used.