Author: Peng Pei
The light-emitting diode LED and the transistor V1 and the potentiometer W1, and the potentiometer W1 or the like are constitute a charging constant flow source. Since the forward pressure drop on the LED is very stable, there is a function of regulating, which is added to the emission junction of V1 and W1, R2. When the W1 resistance can be changed, the base current of V1 can be changed. After the current flow is enlarged, it is charged to the capacitor C1 through the diode D1. The smaller the W1 resistance, the faster the charging speed is, that is, the faster the rising speed output from both ends of C1. When the voltage of C1 rises to a certain value, the output state of the NE555 integrated circuit IC is flipped, and the high level is changed to a low level, and the corresponding triode V2 is saturated. The discharge constant current source composed of diode D2, D3, and triode V3 and potentiometer W2 begins. Similarly, since the forward pressure drop on D2, D3 is very stable, there is a function of regulating, which is added to the emission junction of V3 and W2, R5. When the W2 resistance is changed, the base current of V3 can be changed. At this time, the capacitance C1 is discharged. When the voltage of the C1 drops to a certain value, the 3 pin output of the NE555 integrated circuit is turned to a low level, corresponding to the high level. 7 feet are also low, but due to the function of diode D1, C1 cannot be discharged through 7 foot, and can only be discharged through V3 constant current source. The smaller the W2 resistance, the faster the discharge speed is, that is, the fast-down speed of the sawtooth voltage output from both ends of C1. Since the output signal of this television scanning mosainer is given to the oscilloscope, the input impedance of the oscilloscope is very high, so the charging and discharge of the capacitor C1 are very small. The W1 in the figure corresponds to the field forward scan speed potentiometer; W2 corresponds to the field reversal scan speed potentiometer, which is powered by power switch K. The red junction column is the signal output and the black terminal is the output ground side.
Component List: 1 block (1C below); 1 in the following figure (1C below) (1C in the following figure) (W2 in the following figure, adjusting the sawtooth wave falling speed); 100K potentiometer (W1 in the figure, adjust the sawtooth Wave rise speed), 1 LED light emitting diode (power supply indication and voltage regulation of charging constant flow sources); 2 of 9012 or A1015 triode (V1, V2), 9013 triode (V3) 1N4148 Diode 1 (D1 in the following figure, block the oscillation capacitance to the time base integrated circuit 7 foot discharge); 2 of ordinary diode (D2, D3, D2, the voltage constant fluctuation), small power) 5.6K resistor 2 (R1, R4 below); 1 small power 560Ω resistor (R2 in the figure below); 1 small power 15K resistance (R3 in the figure below); 1 small power 2K resistance (below R5), red, black connection wires; 1 9V battery. Demonstration step: 1. Select a high-profile screen, and the X-axis scan frequency can be adjusted relatively low oscilloscope, such as the J2458 teaching oscilloscope. 2. Install a 9V battery in the TV scan demonstrator. 3. Use the signal line to connect the red wiring column on the TV scan presentation to the "Y input" end of the oscilloscope, and the black wiring column is connected to the "ground" end of the oscilloscope Y axis. Y axial DC input selection is dial to "DC". 4. The "scanning range" on the oscilloscope × axis is adjusted to the lowest "10-100", "scanned microwave" is rotated to minimal. 5. TV scan demonstrator on the playback speed potentiometer W2 counterclockwise, so that the speed of the field is slower. 6. Turn on the oscilloscope power supply, adjust the wave "X-axis gain" and the X-axis shift button, so that the highlight is filled with the fluorescent screen in the left and right directions. 7. By clockwise rotationally rotating the predeterminal scan speed potentiometer W1, and adjusts the "Y-axis gain" and the Y-axis shift button on the wave, the highlight is simultaneously filled with the fluorescent screen in the vertical direction. At this point, you can see that the highlights are moved by slow Iman, but also do the up and down movement. Seriously observe the law of electronic scan, especially the field forwarding and field offset scanning. 8. Separately rotate the predetermined step forward scan speed potentiometer and field reverse scan speed potentiometer, respectively, respectively, respectively, and observe the change of electronic scanning. 9. Adjust the scanning speed of the oscilloscope X-axis. Turn the "scanning range" of the oscilloscope X-axis to "1K-10K" while adjusting the resistance of W1 and W2 on the presentation to minimize, at which time you can see a full-screen grating. At this time, increase the Y-axis or reduce the Y-axis gain, which can be found to be compressed up and down. The horizontal scan of the oscilloscope is stopped, only a vertical bright line appears on the phosphor screen. 10. Detonate the "scan microwave" of the oscilloscope × axis, and more than 10 stable fields can appear on the grating. It can be seen that the demo can see how much the backfunction is related to the field reverse scan speed of the presentation and the × shaft scan speed of the oscilloscope.
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