Instructions

Circuit 43: Active 7.8V battery monitor

Setup information

Install the two transistors, the LED and the nine resistors as shown in Fig. 2.43. Then install the two elec-

trolytic capacitors. The fourteen jumper wires come next. Check the placement on the board again and only

then connect the battery.

Components required:

1 x 2N3906 transistor,

1 x 2N3904 transistor,

1 x BAT 85 Schottky

diode, 1 x red LED,

1 x 470 kΩ resistor,

1 x 100 Ω resistor,

1 x 47 kΩ resistor,

1 x 22 kΩ resistor,

1 x 6.8 kΩ resistor,

2 x 1 kΩ resistors,

2 x 220 Ω resistors,

2 x 10 μF electro-

lytic capacitors,

1 x breadboard, 1 x 9V

battery with clip con-

nector

Fig. 2.43: Active 7.8V battery

monitor

Experiment

An electronic active battery monitor provides information about the status of the monitored battery at any

time. Our circuit here shows the following behaviour:

Battery voltage indicator LED

steady lit, if greater than 7.8 V up to a maximum of 9 V

ﬂashing, if greater than 6.3 V and less than 7.8 V

not illuminated, if less than 6.3 V

You could also monitor the 9V battery used in this circuit. This

makes a lot of sense for experiments that need to run safely at a voltage from 6.3 V onwards

The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.43.