Signal level indication unit on IVLShU1-11/2. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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In this issue of the magazine, in the "Reference sheet" section, a luminescent indicator of the level of the stereo signal IVLSHU1-11/2, controlled by a built-in microcircuit, is described. It also provides information about the scheme for turning on the indicator, how the node works as a whole, how to set it up, etc.

The experiments were carried out with a copy of the IVLSHU1-11/2 indicator (made in December 1987), which was purchased in one of the Moscow stores. When the indicator was turned on, it turned out that it was different from those described in the reference books. Firstly, the current through the control inputs (pins 6 and 7) had a flowing direction and a noticeably larger value (100 ... 150 μA). Secondly, all the elements in the scoreboard were green in color, but differed in structure. In both lines of the display, the first eight elements, indicating the average signal level in the channel (-20 ... 0 dB), each consist of three strokes that turn on simultaneously. Each of the last three elements for indicating the peak level (1 ... 5 dB) is a solid luminous field of a square shape. Note that in the foreign analogue of the device, all elements also have a green glow.

One of the practical variants of the indicator switching circuit is shown in fig. 1. The input low-frequency signals of the right and left channels are fed to the inputs Uin.p and Uin.l. Converters U1-U4 generate DC signals proportional to the average voltage value of each channel (U1, U3) and the peak value (U2, U4). Through the switches DD2.1-DD2.4 and emitter followers on transistors VT1, VT2, these signals are fed to the inputs of the analog-position indicator converters.

The voltage that controls the inclusion of elements that indicate the average level is applied to input 1 of the control (pin 6) of the indicator in a negative polarity relative to pins 2 and 3. The voltage for indicating the peak values ​​of the signal is connected to the control input 2 (vyv.7).

Switches DD2.1-DD2.4 open and close in pairs alternately under the action of two paraphase output signals of the clock generator, assembled on logic elements DD1.1-DD1.4. The generator frequency is about 300 Hz (this value is not critical), the duty cycle of the signals is close to two.

At a single logic level, at the output of the element DD1.3 (0 ... -1 V relative to the common wire), the switches DD2.1 and DD2.2 are open, the signals from the outputs of the converters U1 and U2 of the right channel pass to the corresponding indicator inputs. At the same time, a zero logic level (-4 ... -8 V relative to the common wire) is supplied to the indicator channel selection input (pin 9) and the display line corresponding to the right channel is turned on.

The medium-level AF signal illuminates the elements in group 1-8 of the right indicator line, starting from the first, and the greater the signal voltage, the greater their number is turned on. The peak component illuminates elements 9-11 of the right ruler in the same way. Switches DD2.3, DD2.4 are closed at this time, and the elements of the left indicator line are turned off.

As soon as level 1 appears at the output of the DD1.4 element, the left indicator line turns on and the converters U3, U4 come into operation, the switches DD2.3, DD2.4 open - the left channel works.

Emitter followers serve to reduce the influence of the input current of the analog-position converter on the charging and discharging time of the capacitors of the converters U1-U4. The zener diode VD1 generates a bias voltage that reliably closes (along the grids) the elements of the indicator lines that are not included at one time or another.

The position of the trimmer resistor R7 determines at what minimum input voltage the first element of the line will turn on (the bottom or left on the scoreboard - it is the first in the group of average values). In the same way, resistor R8 can change the threshold for switching on the ninth element of the line (it is the first in the group of peak values).

Note that during the tests of the indicator, the results of which are presented below, converters U1-U4 were not used. The trimmer resistors R1-R4 were connected directly to the inputs of the switches DD2.1-DD2.4, and an adjustable constant voltage was applied to the stereo input. You can read about how such converters are arranged and work in the article by I. Isakson, V. Zaika, P. Kolesnikov and N. Salo "Modern cassette tape recorder" (Radio, 1984, No. 10, pp. 33-35) or in book by Yu. Bystrov, A. Gapunov and G. Persiyanov "One Hundred Diagrams with Indicators" (M.: Radio i Svyaz, 1990).

On fig. 2 shows the dependences of the voltage that needs to be applied to the control inputs of the indicator to turn on a different number of elements in each line, on the left - for average values, on the right - for peak ones, taken at different positions of the knobs of resistors R7 and R8. It can be seen that the position of the initial sections of the curves strongly depends on the resistance of these resistors, on the one hand, and on the other hand, the turn-on voltage of the last element in the groups is fixed at about 5,5 V (for the test specimen). Turning the elements on and off when the signal level changes is quite smooth.

From the examination of the curves it is also clear that the type of dependence of the length of the luminous line of elements on the input voltage required for such an indicator - the dependence must be logarithmic - is not maintained for any value of the resistance of the resistor R7. Therefore, the digitization of the scale in decibels, available in the indicator, is very arbitrary and can only serve to assess the signal level, and not to measure it.

The required ratio of the signals applied to the input of the converters U1 and U2 for the right channel (U3, U4 - for the left one) is set by trimming resistors R1 and R2 (R3, R4).

If you fix the voltage at the input of the channel selection signal of the HL1 indicator (pin 4) at 0 or -9 V relative to the common wire, the indicator will work as a single-channel one. In this case, both the generator and the switches DD2.1-DD2.4 become unnecessary.

Calibrate the device, assembled according to the scheme in Fig. 1, as follows. The trimmer resistors R7 and R8 are set to the maximum resistance position. The inputs Uin.pr and Uin.l are interconnected and a low-frequency sinusoidal signal with an amplitude corresponding to the level of 0 dB is fed to them. Trimmer resistors R2 and R4 achieve half the brightness of the elements that indicate this level in the "right" and "left" lines, respectively. By reducing the input signal voltage to a level corresponding to -20 dB, the slider of the resistor R7 is set to a position in which the first elements of the lines remain on.

In the same way, resistors R1 and R3 set the threshold for turning on the last (eleventh) elements of the indicator lines at a signal level of +5 dB, and resistor R8 achieves the inclusion of the "+1 dB" element at the corresponding input signal level.

Author: S. Biryukov, Moscow

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