battery voltage indicator - in the green or in the red?

4-30 — elektor april 1980 battery voltage indicator d e a )r in thegreen or in the red? It can be rather a nuisance when a car battery goes "dead". This can happen if the lights are left on after leaving the car, but it can also be the result of a fault in the electrical system — where the battery is not charged properly. An "early warning" system that gives an continuous indication of the battery condition is a useful accessory. As described here, only a few components are needed to obtain an "optical" indication: a single lamp that changes colour from green to red as the battery goes into the danger area. 1 The circuit in figure 1 uses a two-colour LED as an indicator. Below a certain threshold (12 V, for instance) the LED lights up red to indicate that the battery is low. When the battery is fully charged, the LED will be green. The colour changes gradually from red to green as the voltage increases. The heart of the circuit is an LM 10 (C) (National). This IC contains a re...