Thermostable pulse generator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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The K561TL1 chip (foreign analogue - CD4093B) is very popular among radio amateurs. You can build a variety of devices on it, because this microcircuit contains four 2I-NOT elements with the transfer characteristic of the Schmitt trigger (hysteresis). In particular, K561TL1 can be used as a generator of rectangular sound signal pulses (Fig. 1), operating in a wide frequency range. The frequency of the generated pulses depends on the ratings of the elements R1 and C1.
Fig. 1
Adding an LED to the classic circuit provides much better thermal stability (small deviations in the frequency of the output pulses with temperature fluctuations.
Shown in fig. 2 oscillator is quite competitive with crystal oscillators. The resistance of the resistor R1 can vary over a wide range (from units of kilo-ohm to 10...15 MΩ). Capacitance C1 also successfully varies from 100pF to 50uF. In this case, the smaller the capacitance C1 and the greater the resistance R1, the higher the frequency of the output pulses. For better thermal stability, capacitor C1 must be used non-polar, with TKE (temperature coefficient of capacitance) H70 or M75. With the ratings of the elements indicated on the diagram, the pulse frequency is 1 kHz. A low-power piezoelectric capsule HA1.2 is connected to the output of the DD1 element, which converts the generator pulses into an audio signal. For the specified capsule, additional signal amplification is not required.
Fig. 2
If a stabilized source with a constant voltage of 1 V is used to power the classical circuit (Fig. 12), when Upit decreases by 1 V (by about 10%), the frequency of the output pulses also decreases, but by 1%. Thus, the ratio of the change in the supply voltage to the change in the frequency of the output pulses is 1:10, respectively. In some practical cases, this is unacceptable.
In the generator circuit in Fig. 2, the ratio is about 1:200. And with fluctuations in the supply voltage in the range of 11 ... 15 V, the frequency change is not noticeable at all. As an HL1 LED, in addition to that indicated in the diagram, it is permissible to use any LED with a continuous glow, for example, L63SRC.
It is not difficult to give the generator additional features if a blinking LED is used instead of the usual LED. Almost any type of flashing LED is suitable here. A diagram of such a generator is shown in fig. 3. HL1 LED plays the role of a current interrupter. Instead of the LED indicated in the diagram, you can use L816BRSC-B, L-769BGR or similar. While the node is running, it flashes.
In this circuit, the need for capacitor C1 is eliminated. The generator works due to feedback through the resistor R1 and its own generation of the HL1 LED. The output sound is intermittent: pause 0,8 s, sound pulse 1,2 s, etc. When the supply voltage changes, the frequency remains stable.
It is convenient to use such a node as a light and sound signaling device in various toys, security devices, etc. It does not need to design a printed circuit board.
If instead of the specified emitter HA1 in this embodiment, a capsule with a built-in generator is used, for example, FMQ-2015B, then the sound signal will resemble a police siren: the sound frequency will change by 170 ... 300 Hz in time with the flashes of the HL1 LED.
You can go even further and use the interrupted emitter KPI-4332-12. Then a three-tone iridescent sound is obtained. For "softness" of the sound, it is worth installing a non-polar capacitor with a capacity of 1 ... 1000 pF in parallel with HA6800. To increase the sound volume, it is necessary to use a more powerful HA1 emitter, for example, SP-1, NS0903A, and equip the node with a current amplifier based on any medium power transistor (KT817).
Author: A.Kashkarov, St. Petersburg
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