Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 37

Circuit 14: Threshold voltage green LED
Setup information
Install the diode as shown in Fig. 2.14. Install the two resistors. Now it is time for the jumpers. Connect the
moving-coil instrument. Check the placement on the board again and only then connect the battery.
Experiment
If everything is wired correctly, the moving-coil instrument will show a strong deflection. This indicates the
so-called threshold voltage of the diode. This voltage must have at least forward current applied, so that
current can flow through the diode. At lower voltage, neither forward nor reverse current is flowing. In our
present case, we are measuring the threshold voltage of a green LED, which is typically 2.1 V.
You can use this circuit to determine the type of an unknown diode. Write down the above measured value
of the moving-coil instrument. If the unknown diode shows the same value, we have a green LED.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.14.
Components required:
1 x green LED, 2 x 1 kΩ
resistors, 1 x moving-coil
instrument, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.14: Threshold voltage
green LED
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