Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 215

Circuit 192: Simple active probe with moving-coil instrument
Setup information
Install the two transistors, the three diodes, the six resistors, the ceramic capacitor and the two electrolytic
capacitors as shown in Fig. 2.192 The seventeen jumper wires come next. Last but not least, connect the
moving-coil instrument. Check the placement on the board again and only then connect the battery.
Experiment
The active probe operates in a frequency ranging from 100 Hz to approximately 1 MHz. The needle deflection
of the moving-coil instrument corresponds approximately to the level at the tip of the probe.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.192.
Components required:
1 x 2N3904 transistor,
1 x J111 FET transistor,
2 x 1N4148 silicon diodes,
1 x BAT85 Schottky diode,
1 x 1 kΩ resistor,
2 x 2.2 kΩ resistors,
2 x 10 kΩ resistors,
1 x 1 MΩ resistor,
1 x 100 nF ceramic
capacitor, 2 x 10 μF
electrolytic capacitors,
1 x moving-coil instru-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.192: Simple active probe
with moving-coil instrument
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