Abstract: A telltale for sensing and responding to ambient light levels. A photosensor monitors light levels and causes a bulb or other controlled element to be energized if ambient levels reach a threshold. In one embodiment a time delay is instituted between sensing the threshold light level and bulb energization. This prevents false triggering on transitory conditions. An additional embodiment has a threshold level that uses hysteresis to avoid unstable sensing near the threshold level. A preferred use for the telltale is in apprising a motor vehicle operator when to turn on the vehicle headlamps.

Abstract: An electronic reostat circuit having a pulse width modulated output for controlling energization of a device such as a vehicle dashboard illumination lamp. A comparator circuit compares a reference signal adjusted by a user with an alternating signal, preferably a saw tooth waveform, and generates a pulse width modulated output whose duty cycle varies directly with the size of the reference signal. The reference signal is generated by a tapped resistor array wherein contacts on the array are coupled to ground by a rotary switch contact which can be adjusted by the user. By raising and lowering the reference signal, the duty cycle can be changed from a minimum to maximum and thereby produce a minimum and maximum lamp illumination signal.

Abstract: A control for a resistive heating element embedded within a motor vehicle seat. A transistor is biased into conduction to energize the heating element when the temperature of the element is below a threshold that is adjusted by the vehicle operator. A fault sensing system monitors operations of the control and de-energizes the heating element if a fault is sensed.

Abstract: A pulse width modulation control unit for energizing a vehicle head lamp. During daylight operation of a motor vehicle the control unit energizes the head lamp by pulse width modulating the battery output and coupling the modulating output across the head lamp. As battery voltage changes the pulse width modulation is adjusted to maintain power output of the head lamp. An over current condition in a switching transistor is monitored and used to de-activate the pulse width modulation of the head lamp energization.