By producing the presented circuit between the lamp as well as the supply, the expected blown brake light bulb indicator could be conveniently constructed and executed in every vehicle.
The performance is reasonably easy:
The IC 555 is configured as a simple voltage comparator, where its pin2 results in being the sensing input.
The BC557 alongside the linked R1, R2 resistors forms a current to voltage converter stage.
Assuming that a working bulb lamp continues associated across the proven points, a small negative potential corresponding to the bulb current consumption is designed across Rx.
This potential evolves into satisfactory to continue the BC557 turned on and performing which sustains pin2 of the IC high.
With the above situations, pin3 of the IC stays low and the LED continues to be switched off.
In spite of this in an event the car bulb fuses or quits illuminating, the potential across Rx fades away or eliminates to an range where the BC557 merely quits executing.
This quickly offers pin2 of the IC high as well as the LED commences glowing suggesting the blown brake light bulb situation to the user.
The above design could be moreover efficiently employed in numerous purposes which desire some form of current (amp) supervising for instance an over-current or over-load cut off etc.
R1 could be measured provided below:
R1 = 0.7/bulb current rating
The above discussed circuit could be significantly made easy by way of the following cofiguration: