Active Battery Monitor - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.17 Active battery monitor

Circuit 42: Active 8.5V battery monitor
Setup information
Install the two transistors, the two diodes and the eight resistors as shown in Fig. 2.42. Then install the two
electrolytic capacitors. The fourteen jumper wires come next. Check the placement on the board again and
only then connect the battery.
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 8.5 V up to a maximum of 9 V
flashing, if greater than 7.0 V and less than 8.5 V
not illuminated, if less than 7.0 V
You could monitor for example the 9V battery used in this circuit. This makes a lot of sense for experiments
that need to run safely at a voltage from 7 V onwards.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.42.
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 kΩ resis-
tor, 1 x 47 kΩ resistor,
1 x 22 kΩ resistor,
1 x 6.8 kΩ resistor,
1 x 1 kΩ resistor,
2 x 220 Ω resistors,
2 x 10 μF electrolytic
capacitors, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.42: Active 8.5V battery
monitor
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