| 摘要 |
PURPOSE:To prolong the life of a projection source and to reduce its power consumption by determining the quantity of projection light in distance measurement on the basis of past measured distance values. CONSTITUTION:A control part 5 decides on the quantity of projection light on the basis of past measured distance values. The control part 5 turns on a transistor TRQ1 at specific intervals to emit infrared rays from the projection source 1 to a subject OBJ, and takes a distance measurement. It is judged whether the last and current measured values indicate short distances or not, and when at least either one indicates long distance, a high-level signal is outputted from an output part O2 to turn on TRs Q2 and Q3. The voltage of a power source VCC is therefore applied to a capacitor C as it is. When the subject is at short distance, the output of the port O2 falls to a low level to turn off the TRs Q2 and Q3. The capacitor C is charge through a Zener diode ZD, diode D, and resistance R6; the voltage drop across the diode ZD is large, the applied voltage to the capacitor C is low, and the energy charged in the capacitor C is reduced to decrease the quantity of projection light. |
