Failure Switch Monitor for Car Lamps/Bulbs

Figure 1 

The circuit has been designed for use on cars and other types of vehicles that would provide an indication during a failure of the lamps or bulbs.

• LM741 – a general purpose single operational amplifier with features such as offset null, compensated internal frequency, voltage range with high input, good stability of temperature, and protected from short circuit
• BC214 – a complementary silicon planar epitaxial transistor used in AF small signal drivers and amplifiers as well as for low noise preamplifier applications due to its feature of good linearity of DC current gain

The circuit consists of two parts where the first part is a switch responsible for sensing the presence of a DC current. The current that will be applied will originate from an 8 V to 16 V supply. The value of the resistor R1 should be set to be able to produce and generate a voltage of approximately 100 mV. This voltage will be required for the trip current is it becomes triggered. The 1K Ohm trimmer RV1 is used to adjust the sensing point of the circuit and the current trip.

The second figure illustrates the operation of how the circuit can be can be made to function as a car lamp failure switch. This circuit will be triggered to turn ON if any lamp that is being monitored suddenly gets damaged or burns out. In series with the wiring harness is the resistor R which is fed to a selected cluster of up to four lamps which are rated with similar values which are grounded to the car chassis. The relays are used for each of the circuits to be triggered for their functionality.

Figure 2 

The use of this car lamp failure switch may be seen being applied to brake lamps which are high in quality. This will provide a failure warning in the event that any of the bulbs have been damaged. In some designs, the voltage dependence of the car indicator lamps is also compensated for lamp failure while some warning indications of lamp failure are by means of frequency doubling.

Source:users.otenet.gr/~athsam/car_lamb_failure_swittch.htm