Television makes simple oscilloscope ----- TV Oscilloscopes

TV made simple oscilloscope, TV Oscilloscopes Keywords: TV do simple oscilloscope TV made simple oscilloscope Using an additional circuit board to be observed input electrical signal, the output signal of the TV to video input interface, a waveform can be displayed on the screen of the electrical signal. The circuit configuration in FIG. 1, FIG 2 brother actual circuit. Oscillation circuit Circuit 555 generates a horizontal synchronizing signal and the sawtooth signal, the output period tH = 0.693x (Ra + Rb) C1, tL = 0.693 × RbC1. The input circuit To the signal input port being observed, SWl is AC / DC selector switch, closing the DC, AC disconnect; waveform positioning on the television screen by VR3 adjustment, the adjustment range of the sawtooth signal voltage range (1 / 3Vcc ~ 2 / 3Vcc) Similarly, C3, C4 voltage terminal VR3 stabilizing effect; the size of amplitude of the waveform is adjusted by potentiometer VR4. Control circuit The sawtooth wave signal generated by the oscillator and the input signal to the comparator IC2a ​​pulse width modulation (PWM), generates a PWM signal, then uses the falling edge of the differentiating circuit taken PWM rectangular wave pulse obtained corresponding to the input signal. Charging time constant of the differentiating circuit t = R9C6 = 0.22μs, discharge time constant t = (R8 + R9) C6 = 0.44μs. IC2b inverting input pulse signal. The image signal output The signal outputted by the inverter circuit IC2b Tr1 an emitter, with the horizontal synchronizing signal from the composite video signal outputted IC2c; R12 is a 75-ohm resistance, in order to get close to the 75-ohm impedance matching. Circuit adjustment This oscilloscope oscilloscopes ordinary time axis is the vertical direction, the horizontal direction is the voltage axis. The video input terminal and its output terminal is connected to the television, VR3, VR4 is rotated to the intermediate position, and then adjusting VR1, VR2 to achieve horizontal synchronization, so that a vertical white line (axis) appears on the screen, and then adjust the white line movement VR3 to the central position; the input signal at the signal input end of the observation, by adjustment VR4, the measured waveform can be shown on the display screen. This oscilloscope signal frequency of 10kHz or less observable.

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