Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 208

Circuit 185: Peak level display with LED
Setup information
Install the transistor, the diode and the four resistors as shown in Fig. 2.185 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 moving-coil instrument shows deflection at an NF input
voltage of 0.3V and full-scale deflection at an NF input voltage of 1.5V. 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. 3.185.
210
Components required:
1 x 2N3904 transistor,
1 x BAT85 Schottky
diode, 1 x 220 Ω resis-
tor, 1 x 1 kΩ resistor,
1 x 10 kΩ resistor,
1 x moving-coil instru-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.185: Peak level display
with moving-coil instrument