Car Lights Monitor

003 CAR ELECTRONICS A defect car light is at best a nuisance and at worst a danger. Fortunately, most new cars are equipped with suitable monitors thast indicate on the dashboard whether a light is not working. There are, of course, millions of older cars that have no such sophistication and it is for these that the present monitor is intended. Two special ics are available from Telefunken that are de- signed for measuring the current through a light bulb. In practice, detecting whether a current flows through a bulb or no is a most suitable way of determin- ing whether the bulb still works. If a small resistance is con- nected in series with the bulb, a small voltage drop will develop across it when the bulb lights (R1 can cope with only two bulbs, so needed. The junction of the bulb of the inputs (pin 4 or pin 6) of the ic. The potential across the resistor is compared in the lc with an internal reference voltage. Depending on which of the two ics is used, the voltage drop must ...