Simple Battery Monitor - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.84 Simple battery monitor

Circuit 181: Simple 7.5V battery monitor
Setup information
Install the two transistors, the diode and the four resistors as shown in Fig. 2.181 followed by the ten
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 7.5V, 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. 3.181.
206
Components required:
2 x 2N3904 transistors,
1 x red LED, 1 x 2.2 kΩ
resistor, 2 x 10 kΩ resis-
tors, 1 x 22 kΩ resistor,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.181: Simple 7.5V battery
monitor