Monitors battery voltage, Three-LED Display. Connecting this circuit to the battery of your vehicle, you will always know at a glance the approximate voltage available. An indication of battery voltage is useful to the motorist for monitoring the battery's capacity to deliver current, and as a check on the efficiency of the dynamo or alternator. Threshold voltages of the Leds are set by means of two Zener Diodes (D6 & D10) plus two further Diodes wired in series (D4, D5 and D8, D9 respectively) adding a step of about 1.3V to the nominal Zener voltage. Parts: R1 = 1k R2 = 100K R3 = 1k R4 = 3.3K R5 = 3.3K R6 = 1k R7 = 3.3K R8 = 3.3K Q1 = BC547 Q2 = BC547 Q3 = BC557 D1 = Red Led D2 = Amber Led D3 = 1N4148 D4 = 1N4148 D5 = 1N4148 D6 = BZX79C10 D7 = Green Led D8 = 1N4148 D9 = 1N4148 D10 = BZX79C12 Notes: Red LED D1 is on when battery voltage is 11.5V or less. This indicates a low battery charge. Amber LED D2 is on when battery voltage is comprised in the 11.5 - 13.5V range. This ...