Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 66

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.
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.
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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