The behavior of a diode is described by its characteristic curve. It shows that no measurable current flows up to a certain voltage, but then the current rises steeply. Overall, the current increases exponentially. On a linear scale, there appears to be a knee point, which for silicon diodes is approximately 0.5 V and for LEDs is around 2 V, depending on the color.

Measurement of Diode Voltages

Using TestLab and the TLScript scripting language, which were introduced in two other articles in this issue, various diodes are examined here. First, a red LED with a 1 kΩ series resistor is connected to four port pins (Figure 1), which are configured as inputs. The data direction is set to input with Pdir = 0. When Pout = 1 is set, the first connection, P0, remains an input, but at the same time an internal resistor of approximately 35 kΩ to VDD is activated in the Arduino Nano, allowing a small direct current to flow through the LED.

Figure 1: Diode voltage measurement.
Figure 1: Diode voltage measurement.
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