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Voltampere LED characterization
(approximate determination of Planck's constant)


Measurement principle

The measurement principle of this role is based on the standard method of measurement of V-A characteristics of the electronic element. With the variable power changing voltage at the measuring element (here LED) and amperemeter, which is connected in circuit subtracting the size of the electric current. For measurement of the diodes in the forward direction is still in the circuit even included a protective resistor to prevent a steep current increase and subsequent destruction of the diode after exceeding a threshold voltage. Schematic diagram of the electrical circuit is shown in Figure 1

schema zapojeni V-A charakteristiky

FIG. 1 - Schematic diagram of the experiment for measuring the V-A characteristics of the LED

We start from the same scheme in the case of our remote experiment CEcIL. The regulated power supply and measuring instruments replaces measuring USB card K8055. Digital-to-Analog output is current strengthened and serves as a regulated power supply with a maximum voltage of about 5 V. A pair of analog-to-digital inputs are used as a pair of voltmeters. One measures the voltage on the measurement of LED, the second measured voltage to the ballast (protective) resistor. From knowledge of the voltage on a linear element (resistor) can use Ohm's law to determine the current flowing through the resistor. This is due to the serial connection (see schema - Figure 1) is the same as the current in the whole circuit, thus the current through the LED. Five Card K8055 digital outputs are then used to select one of five LEDs that can be measured. The effect of passing current (such as the LED, or the rate of sunshine) can be observed via Webcam.

pohled na ulohu CECIL
panel ulohy CECIL

Both values, ie voltage ULED and current ILED, are retrieved and displayed on the control panel in the web browser on the client side. Thus, the measured values can be stored to a table (file) and continuously displayed on the graph. Continuous display of values in the graph directly on the measuring task panel is mainly used for checking the accuracy of the measured data, and to find the characteristics of places where it is necessary to assess the tax required data. To complete the processing of the specified work assignment, data can be saved to your PC and then processed in any spreadsheet program.

Video tutorial