TinyProjector Lab Notebook

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The biggest challenge for designers of mobile communication devices is presenting large amounts of information on very small displays. As the form factor of these devices continues to get smaller and our demand for mobile information continues to grow, the task only gets more difficult.


The solution to this dilemma cannot simply consist of adapting design principles, like the desktop metaphor, to fit the limited real estate. Adding projection capabilities to the mobile device itself might pose a possible solution to this problem.


The basic idea of TinyProjector is to create the smallest possible character projector that can be either integrated into mobile device, or linked dynamically with wireless RF connections like serial low range transceivers.


After extensive research, and having explored many non-viable alternatives, a completely new prototype (number 9) was designed and built, making intensive use of 3D modeling CAD software and the 3D printer.


The overall design is radically simplified and miniaturized. Compared to all the earlier versions, which used laser diodes salvaged from cheap key chain laser pointers, the current prototype has smaller low-cost low-output laser diodes that allow for just one row of eight lasers instead of two interlinked rows of four lasers, making cumbersome primary deflection mirrors obsolete.


A micro motor with a single swiveling servo arm, making a continuous full 360-degree rotation, drives the deflection mirror, resulting in a 38-degree left-right sweep. This leads to an unusually high overall laser projection angle of 104 degrees.


All body parts of the prototype, including the critical lens assembly and mirror holder, were designed completely in CAD software, and then 3D printed in ABS plastic.


The system is now closed loop: an IR LED/photodiode combination signals the PIC chip when the mirror is at its origin, which enables a precise overlapping of the laser pulse sequences.


Compared to the earlier prototypes, a PIC chip with more memory (and EEPROM) is used in the current prototype, which allows storing character templates for the complete alphabet as well as some special characters.


A two-way serial port connection with both Palm PDAs and Java enabled cellphones is demonstrated. From either device, arbitrary text can be sent to the projector and is displayed; in addition to that, preset text lines stored on the projector itself can be triggered from these devices.


The current prototype is capable of displaying 8 characters, each consisting of an 8x5 pixel matrix. (However, tests have shown that the horizontal resolution can be easily increased by at least factor 10, and the vertical distance between the laser beams could be reduced by factor 2. In such a configuration, the prototype could project two to three times more characters than the current prototype.)


Very important, the projection refresh rate of the third prototype is increased to about 25Hz, which is significantly higher than the earlier prototypes that had a refresh rate of only about 3Hz, and therefore had to rely on the effect of persistence of vision. The projection of the current prototype appears stable, easy to read, and—after intensive debugging and mechanical tuning—almost jitter free. However, the overall brightness of projection is lower than of the projectors based on persistence of vision, due to the increased refresh rate. Furthermore, the amount of vibration has increased, which is due to the higher RPM of the micro motor, together with the inherent inertia of the stainless steel mirror. Nevertheless, the primary goal of TinyProjector prototype 9 was to make the projection "usable" and readable. This goal has been met.


In order to document this work, an extensive lab notebook has been written, including several hundreds of pictures, scans, screenshots, and movies.

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Send me some comments! Stefan Marti Last updated February 23, 2003.

Copyright © 1997-2004 by Stefan Marti and MIT Media Lab. All rights reserved