Display of eight signals on the oscilloscope screen. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Display of eight signals on the oscilloscope screen. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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Rapidly developing modern digital electronics requires radio amateurs to have deep knowledge and good measuring equipment. If the first is quite achievable, then the second, with the enormous high cost of imported equipment and obsolete domestic equipment, leads to a dead end, from which a way out can be found through joint efforts.

In the process of setting up sequential logic circuits, a radio amateur may need to simultaneously observe several signals. In this case, it is most important to know the logical states and moments of signal change, and the exact values of voltages and durations of edges are less significant. You can view two, four, or eight digital signals simultaneously on the oscilloscope screen. Digital signals are treated as purely logical and are gated by a digital multiplexer. Although this does not preserve voltage levels and precise mode shapes, maximum performance is achieved with a relatively simple circuit.

(click to enlarge)

The circuit (see figure) allows you to display a large number of signals using one oscilloscope channel. After each sweep of the oscilloscope, the contents of the divide-by-16 counter (DD2) are incremented by one [1]. The counter output code controls the selection of the inputs of the digital multiplexer DD1 and the analog multiplexer DD3, while the counter input stage is used to obtain the channel “interleave” mode, in which the counter output code changes only every second scan cycle.

The highest three digits of the counter provide selection of the input signal passing through the digital multiplexer DD1, and at the same time selection of the magnitude of the DC voltage taken from the resistive divider and passing through the analog multiplexer DD3.

This voltage is added to the digital signal to provide a different reference voltage level at each sweep cycle, so that as each digital signal is displayed, the electron beam on the oscilloscope screen is shifted vertically by a certain amount. Variable resistor R6 serves to adjust the vertical shift of the beam, so the distance between the images of different signals on the screen can be changed. You can use the vertical sensitivity control included in the oscilloscope to adjust the amplitude of the images.

Potentiometer R2 is set in such a way as to obtain the best transient response of the vertical amplifier of the oscilloscope. Both potentiometers R2 and R6 must be non-inductive type. Resistors R7-R9 can be used to set the required voltage levels at the control inputs of the multiplexers. The chain of constant resistors can be replaced with eight parallel-connected potentiometers, the sliders of which are connected to the input terminals DD3, this ensures separate adjustment of the vertical positions of the scan lines for each signal. If toggle switch S1 is opened, only four signals are displayed on the screen (inputs 0, 2, 4, 6 of the digital multiplexer).

If you open both toggle switches S1 and S2, only inputs 2 and 6 are displayed. The strobe pulse is usually removed from the back panel of the oscilloscope. Microcircuits DD1, DD2 can be replaced with any, but they must be functionally similar; DD3 can be replaced with K590KN1 [2]. Any transistor VT2 with a coefficient of at least 40.

References:

Shilo V.L. "Popular Digital ICs"
Novachenko I.V. and others. "Microcircuits of household radio equipment" Ref., 1993

Author: A.V. Kravchenko

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