Dual frequency generator with flashing LED. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Flashing LEDs quickly won the sympathy of radio amateurs. The simplicity of their application compensates for some disadvantages, for example, the relatively high cost and the inability to control the frequency and duty cycle of light pulses. Radio amateurs would not be such if they were not looking for non-standard options for switching on and using various radio components. Flashing LEDs have not been ignored either.

Descriptions of devices in which flashing LEDs were used as low-frequency generators of rectangular pulses have already been published in the technical literature, see, for example, articles [1, 2]. Given that the blinking LED contains a high-frequency master oscillator with a frequency divider, it is not difficult to assemble the device according to the circuit in Fig. 1, in which the flashing LED will simultaneously operate both as a low-frequency generator with a pulse repetition rate of 1 ... 3 Hz, and as a burst generator with a duty cycle of 100 ... 350 kHz.

The bipolar transistor VT1 works as an amplifier-separator of the high-frequency and low-frequency components of the current consumed by the HL1 LED. At the output of the emitter of the transistor VT1, a low-frequency component is distinguished, the amplitude of the pulses here is about 2 V. The amplitude of the bursts of high-frequency pulses (Fig. 2) at the collector output of the same transistor will be about 4 V. The expanded waveform of the high-frequency filling of the pulses is shown in fig. 3. Capacitor C4 acts as a blocking capacitor in the power circuit.

This generator has one interesting feature: if a choke with an inductance of several tens of microhenries is connected in series with the HL1 LED, then the signal at the high-frequency output is "colored" by many high-frequency harmonics. This property can be used, for example, to test radios.

If the generator, made according to the scheme of Fig. 1, supplement with a frequency divider assembled on a CMOS chip and two transistors, as shown in fig. 4, then you get a sound generator of tone pulses reproduced by a high-impedance dynamic head BA1.

On the n-channel field-effect transistor VT1, an amplifier of high-frequency pulses is assembled, which increases their amplitude to the level of the supply voltage. Chip DD1 type K561IE10 is a two-bit binary counter. It is turned on in such a way that at pin 13 the pulse frequency is 128 times less than at the input (pin 2), and at pin 14 it is 256 times less.

The tone and frequency of the beeps depend on the type and instance of the applied LED.

The cascade on the bipolar transistor VT2 is built according to the emitter follower circuit in such a way that a four-level signal arrives at the non-dynamic head, the waveform of which is shown in Fig. 5. By changing the resistors R3 and R4 within small limits, it is possible to change the nature of the sound of the dynamic head BA1. The frequency of beeps can be increased by connecting resistors R3 and R4 to other outputs of the counter DD1.2.

In place of HL1, the author used a blinking L816BYD type LED manufactured by Kingbright, yellow with a brightness of up to 40 mCd and a housing diameter of 10 mm. It can be replaced by any LED from the L816B...L796B... (8 mm), L56B... (5 mm) series or, for example, red matte superbright L796BSRD/B. Flashing LEDs from other manufacturers will also work, but only without the built-in high-resistance current-limiting resistor. The microcircuit can be replaced with CD4520AE, and with a change in the switching circuit - with K561IE16, K561IE20. Bipolar n-p-n transistors - any of the KT315, KT3102, KT645, KT6111, SS9013, 2SC2001 series. Field - KP501A, KP501V, KR1014KT1A, K1014KT1A. Oxide capacitors - K50-35 or their imported counterparts. Non-polar - K10-17. Resistors - S1-4, MLT, S2-23, S2-33.

Literature

1. Butov A. Generators - signaling devices. - Radio, 2002, No. 7, p. 59, 60.
2. Martemyanov A. Signaling devices on a flashing LED. - Radio, 2000, No. 5, p. 67.
3. Butov A. Electronic referee. - Radio, 2002, No. 10, p. 54, 55.

Author: A.Butov, village of Kurba, Yaroslavl region

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