The heart of the MicronEye is the IS32 OpticRAM, developed and manufactured by Micron Technology, Inc. The integrated circuit is Micron's 64K Dynamic RAM assembled in a standard 16 pin ceramic DIP package with a clear glass lid. The IS32 is composed of 65,536 individual image sensing elements called pixels. These pixels are organized into two arrays of 128 rows and 256 columns. (Typical applications will utilize only one of the sensor arrays since the arrays are separated by an optical non-light sensing zone of amplifiers). Each of the elements in the IS32 is a light sensitive capacitor which can be accessed randomly by simply strobing in the appropriate row and column address of the particular element to be accessed.

The device operates by focusing the reflected light from an object onto the 32,768 light sensitive elements of the array. Light striking a particular element will cause the capacitor, which is initially precharged to a fixed voltage, to discharge toward zero volts. The capacitor will discharge at a rate proportional to both the intensity and duration it is exposed to light.

To determine if a particular element is black or white, the user would read the appropriate row and column address associated with the physical location of that particular element. The IS32 would read the voltage value of the capacitor and perform a digital comparison between the voltage of the capacitor and the fixed threshold voltage. The output pin of the IS32 would be set to a logic level of 1 if the voltage on the capacitor was above the threshold point. It would set the output to a logic level of 0 if it was below the threshold voltage.

The logic level of 0 will be associated with a white pixel. A logic level of 1 will be associated with a black pixel. A white pixel indicates the capacitor was exposed to a light intensity sufficient to discharge the capacitor past the threshold point. A black pixel indicates the light intensity was not enough to discharge the capacitor past the threshold, therefore it retained the charge and is read as a logic 1.

The other significant factor affecting the discharge of the light sensitive capacitors is the length of the time which the capacitors are exposed to light. This period of time is measured from the initial exposure of an element until the time the particular element is read or refreshed.

The combination of the light intensity and the scan rate (the amount of time the elements are exposed before being read) will determine the optimum imaging environment. The faster the elements are scanned, or read, the greater the light intensity is required.

Perhaps the most important consideration the user must keep in mind is that the MicronEye requires a high contrast scene in order to image the object onto the IS32. Unlike a TV camera which can respond to "shades of gray," the IS32 is a digital chip where each picture element will only respond to a dark/light (1/0) binary part of the scene around an arbitrary amount of light used as a threshold. Shades of gray can be achieved by averaging multiple scans together using either a different threshold voltage or varying the scan rate. By changing the threshold voltage, keeping both the image and light intensity constant, the outputs produced during each scan will not change where pixels are definitely black or white. Change will be exhibited where the image is gray and the amount of reflected light striking the capacitors is near the threshold voltage. If an area of the image is a dark shade of gray, the output will generate more logic level 1's than logic level 0's. Where the image is a lighter shade of gray the output will generate more logic 0's than logic 1's. By averaging these outputs over a number of scans, the appropriate shade of gray is produced.

The nominal threshold with pin 1 open is 2.1 volts. This threshold can be adjusted via pin 1 from 1.5 volts to 3.0 volts. It is suggested that gray scale capability be achieved by varing the scan rate rather than adjusting the threshold voltage. By varying the scan rate (varying the discharge time) you can more accurately achieve gray scale capability.

If for any reason you must remove the IS32 from its socket, caution is imperative. The IS32 is susceptible to static and can be damaged by static electricity. Removal of the IS32 from the Bullet may require that the tips of the chip extractor tool be bent out slightly to accomodate the narrowness of the Bullet housing. When reinserting an IS32 into the socket, be certain it is properly oriented. For the Bullet, the IS32 is oriented properly when the red edge of the ribbon cable is on the same side of the Bullet as the Pin 1 notch on the IS32. For the Camera, the IS32 is oriented properly when the Pin 1 notch on the OpticPAM is on the same edge as the Pin 1 notch on the other IC's in the camera.