HARDWARE LAB 08 · OPTICAL INPUT / RASTER TIMING

CRT OPTICAL CONTROLLER LAB

Compare two different tricks: a light pen latches live beam counters; a flash-detection gun asks software to show a known bright target.

H COUNT: 000
V COUNT: 000
H SYNC: HIGH
V SYNC: HIGH

THE CONTROLLER DOES NOT SEE OBJECTS.Its photodiode produces one changing voltage. Timing hardware or game software gives that voltage meaning.

SLOWED RASTER VIEW

640 × 480 ACTIVE DISPLAY

BEAM SYNC

The beam animation is intentionally slowed. Click or drag to aim; arrow keys move one pixel and Shift + arrow moves ten. The counters retain the actual 31.47 kHz line and 59.94 Hz frame timing.

TWO-LINE BEAM WINDOW

SYNC + PHOTODIODE SCOPE

25.175 MHz

LIGHT PEN

WHEN did this pixel glow?

A local pulse latches counters tied to the scanning beam. Sensor delay becomes a position error, and a buffered display breaks the timing relationship.

PHOTODIODE → COMPARATOR → H/V LATCH

FLASH-DETECTION GUN

Did this known area become bright?

Software changes the picture, waits, and samples the detector. It can identify a target because it already knows what it flashed—not because the gun returns coordinates.

SOFTWARE FLASH → SENSOR BIT → HIT TEST

01SCREEN LIGHTA scanning spot or software-controlled target reaches the sensor.

02PHOTODIODELight becomes a small analog current and then a voltage.

03COMPARATORA threshold turns the analog waveform into one digital event.

04TIMING / SOFTWARECounters or a known flash sequence infer the intended input.