| 摘要 |
PURPOSE:To improve response of a display and to prevent flicker by utilizing a time constant controlling circuit comprising a nonlinear resistance element, in which the value of the resistance decreases with an increasing car speed and a capacitive element in an electronic speed meter for a vehicle. CONSTITUTION:A car speed pulse from a car speed sensor 9 is shaped to constant width in a monostable multivibrator 8 and with a condenser 6 and a resistance 7, a discharge voltage proportional to a car speed is obtained. When, with a rapidly increased car speed, an output of a buffer amplifier 18 is increased guickly, all of zener diodes 10-12 conduct, a time constant for charging of a condenser 17 becomes relatively small because a parallel synthesized resistance of resistances 13-16 is small and thus response of a display is improved. For a fine variation of a car speed when running with a constant speed, all of the zener diodes do not conduct, a charging time constant of the condenser 17 is determined by the resistance 16, and because it becomes relatively large, flickering of the display is prevented. |
