| 摘要 |
<p>An on/off circuit is provided to automatically turn "on" or "off" a radar warning receiver upon lapse of a preset period of time after an automobile engine is turned "on" or "off". The receiver is powered by a D.C. input signal from the battery of the automobile via its cigarette lighter plug. The circuit includes an on/off switch connected to the cigarette lighter plug and the receiver and being switchable between "on" and "off" states to correspondingly transmit and not transmit the D.C. input signal to the receiver for turning it "on" and "off". A noise sensor is also connected to the cigarette lighter plug for sensing the presence or absence of a varying noise signal superimposed on the D.C. input signal which depends on whether or not the automobile engine is running. The noise sensor senses whether or not the noise signal is present by integrating the input signal and producing a first output signal having an increasing magnitude when the noise signal is present and a second output signal having a constant low magnitude when the noise signal is absent. A time delay in the form of a resistor and capacitor network is connected between the noise sensor and on/off switch and is actuated, after lapse of a preset period of time, between high and low output states in response to the first and second output signals to, in turn, cause the on/off switch to switch between its "on" and "off" states.</p> |
