| 摘要 |
<p>The description relates to a control circuit for recording the actuation of an optical key, in which there is a light-sensitive diode operated in open circuit as a key actuation sensor. A microprocessor circuit monitors the no-load voltage of the diode to differentiate an actuation of the optical key from variations in the brightness of the ambient light. The invention is characterized by an easily producible voltage-time-conversion process for monitoring the no-load voltage. To this end, there is a capacitor connected to the diode which assumes a load operating status corresponding to the no-load voltage of the diode and can be discharged in a discharge operating status via a discharge resistor, where the microprocessor circuit has a high-resistance input port connected to the capacitor to monitor the capacitor discharge and, as a measure of the no-load voltage, determines the time elapsing until the voltage at the input port during the capacitor discharge process reaches a predetermined input port switching threshold.</p> |
