Level Meter - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.86 Level meter

Circuit 184: Peak level display with LED
Setup information
Install the transistor, the two diodes and the two resistors as shown in Fig. 2.184 followed by the jumper
wire. Check the placement on the board again and only then connect the battery.
If you are familiar with the relevant safety guidelines as per VDE and know how to observe them when
working with devices that are to be connected to the mains, you can now connect the audio amplifier.
Experiment
The circuit responds to low-frequency signals. The red LED turns on at an NF input voltage of 0.5V and
reaches its maximum brightness at about 1.5V input voltage. You can test the circuit on the speaker output
of an audio amplifier or perfectly safe on the speaker jack of a portable radio.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.184.
Components required:
1 x 2N3904 transistor,
1 x BAT85 Schottky
diode, 1 x red LED,
1 x 1 kΩ resistor,
1 x 10 kΩ resistor,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.184: Peak level display
with LED
209