Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 205

Circuit 182: Simple 8.2V battery monitor
Setup information
Install the two transistors, the diode and the five resistors as shown in Fig. 2.182 followed by the 13 jumper
wires. Check the placement on the board again and only then connect the battery.
Experiment
The circuit is used to monitor battery voltage. If voltage is less than 8.2V, the red LED turns on. When the
battery breakdown voltage is finally reached, the LED turns off again.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.182.
Components required:
2 x 2N3904 transistors,
1 x red LED, 2 x 2.2 kΩ
resistors, 2 x 10 kΩ resis-
tors, 1 x 22 kΩ resistor,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.182: Simple 8.2V battery
monitor
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