Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 213

Circuit 190: Simple active probe with moving-coil instrument
Setup information
Install the transistor, the diode, the five resistors, the ceramic capacitor and the two electrolytic capacitors
as shown in Fig. 2.190 The seven jumper wires come next. Last but not least connect the moving-coil instru-
ment. Check the placement on the board again and only then connect the battery.
Experiment
The active probe operates within a frequency range from 100 Hz to approximately 1 MHz. The needle deflec-
tion 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. 3.190.
Components required:
1 x J111 FET transistor,
1 x BAT85 Schottky diode,
3 x 2.2 kΩ resistors,
1 x 4.7 kΩ resistor,
1 x 1 MΩ resistor, 1 x 10 nF
ceramic capacitor,
2 x 10 μF electrolytic
capacitors, 1 x moving-
coil instrument,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.190: Simple active probe
with moving-coil instrument
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