LED signal indicator for ULF. Scheme, description

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LED signal indicator for ULF. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

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The low-frequency LED indicator is not only informative, but also looks very attractive in any equipment, which is why it is currently preferred by many musicians over dial indicators. To control LEDs, the foreign radio-electronic industry has been mass-producing specialized microcircuits for a very long time [1, 2]. Unfortunately, these microcircuits can only be found on the radio markets of large cities in the post-Soviet space, so the old amateur radio technique remains - not to chase after "bourgeois things", but to use radio components that are widely used in practice.

In the Czech amateur radio magazine [3], a diagram of such an indicator was given using a quad operational amplifier of the LM324 type. These microcircuits are no longer in short supply and have a minimal cost. The scheme of the device is shown in Fig.1.

(click to enlarge)

The input low-frequency signal is applied simultaneously to the inverting inputs of all the op-amps of the circuit. The potentials of the non-inverting inputs of these operational amplifiers are connected to a resistive supply voltage divider P1, R1...R9. Depending on the ratio of the resistances of these resistors, any characteristic of the indicator can be obtained - both linear, quadratic, and combined, therefore this circuit is suitable for indicating the input signal level of a powerful ULF, for indicating the output power of a ULF and many other purposes.

The trimming resistance P1 sets the required sensitivity of the display device during tuning. The values of the resistors R11...R18 determine the current of the LEDs LD1...LD8. In principle, it is desirable to use components in the circuit that provide sufficient brightness at low currents through the LEDs. This will reduce the load on the output transistors of the op amp chips.

It is advisable to use LEDs of various glow colors in the circuit. This will make such an LED scale of the device more informative. An even greater visual effect can be achieved if a "flashing" LED is used as the LED, which is designed to indicate ULF overload. There is no need to make any changes to the schema.

Let me remind you once again - try to maximize the values of resistors R11 ... R18 from the condition of a compromise between their values \uXNUMXb\uXNUMXband the brightness of the specific types of LEDs used.

The closest domestic analogue of the LM324 chip is K1401UD2. The supply voltage of the microcircuit must be at least 4 V, but not exceed 15 V [4] . The "plus" of the power supply is supplied to pin 11 of the microcircuit, and the "minus" of this power is fed to pin 4. Unfortunately, this information was not given in the original article [3].

Literature

E.L. Yakovlev, Indication microcircuits // Radio components. -#2. -2006. -p.25-29.
E.L. Yakovlev, Indication microcircuits // Radio components. -#2. -2007. -p.26-27.
Indikator vybuzeni pro nf zesilovac // Amaterske RADIO. -#12. -2009. -S.4-5.
A.G. Alekseev, G.V. Voishvillo // Operational amplifiers and their application. - Publishing house "Radio and communication". -M. -1989.

Author: E.L. Yakovlev, Uzhgorod, Ukraine

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