Night light with acoustic switch. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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The device proposed by the author is a self-powered night lamp with an LED as a light source, which can be turned on and off by an acoustic signal, for example, by clapping your hand. It is not difficult to place it in any convenient place, so it will be useful on a tourist trip, hiking and other occasions, since it can serve as a flashlight, and will also be used in various games and competitions "who will clap louder", etc.

The scheme of the device is shown in fig. 1. It consists of a BM1 microphone, a pulse shaper on a VT1 transistor, a single vibrator on a DD1.2 trigger, a DD1.1 counting trigger and a switch on a VT2 transistor. An EL1 LED of increased brightness was used as a light source.

The device works as follows. After the power is turned on, the capacitor C1 is charged through the resistor R2. At this moment, the resistor is at a high level, which is fed to the input R (pin 10) of the D-flip-flop DD1.1 and sets a low level at its direct output (pin 13). Transistor VT2 is closed and LED EL1 is de-energized. Transistor VT1 is also closed and its collector is low.

If you now clap your hands, then voltage surges appear at the output of the BM1 microphone, which through the capacitor C2 enter the base of the transistor VT1 and open it. The collector current increases, and on the load - resistor R4 - one or more (depending on the duration and nature of the clap) pulses are formed with an amplitude close to the voltage of the power source. The intensity of the clapping in the palm of your hand is not always constant, therefore, a different number of pulses appears on the resistor R4 with one clapping. In order for the counting trigger DD1.1 to switch once with each clap, a single vibrator was introduced into the device.

The pulses are fed to the S input (pin 6) of the DD1.2 trigger and set its direct output (pin 1) to a high level, thereby starting the one-shot. Through the resistor R6, the charging of the capacitor C3 begins, and as soon as the voltage on it exceeds approximately half the supply voltage, which will be perceived by the input R of the trigger DD1.2 as a high level, the trigger will return to a low level state at the direct output, and the capacitor C3 will quickly discharge through diode VD1. At the output of the single vibrator, a voltage pulse is formed with a duration T determined by the resistance of the resistor R6 and the capacitance of the capacitor C3:

T \u0.7d 6 * R3 * C3, where the capacitance of the capacitor C6 is in microfarads, and the resistance of the resistor R0,5 is in megaohms. For the values ​​​​of the elements indicated in the diagram - about XNUMX s.

The single vibrator pulse will go to the input C of the D-flip-flop DD1.1. Since the inverting output (pin 12) DD1.1 is connected to the information input D, this turns it into a counting trigger. Therefore, along the edge of the one-shot pulse, it will switch to a state with a high level at the direct output and an opening voltage will be applied to the gate of the transistor VT2, the resistance of its channel will sharply decrease and the EL1 LED will start to shine. The duration of the pulse generated by the single vibrator is several times longer than the duration of the clap, so switching will occur once from one clap. If you now clap your hands again, the single vibrator will again generate a pulse and the counting trigger will switch, but this time to a low level state at the direct output, the channel resistance of the transistor VT2 will increase and the EL1 LED will go out.

All parts of the device, except for the battery and the switch, are mounted on a printed circuit board made of one-sided foil fiberglass with a thickness of 1 ... 1,5 mm, shown in Fig. 2. The board is placed in a case of a suitable size, on which the switch is mounted. Holes are made in the housing opposite the LED and the microphone.

The device used resistors R1 - SPZ-38a, the rest - MLT; capacitors C1, C2 - oxide K50-35 or similar imported ones; C2, C3 - ceramic K10-17, KM-6. The diode can be applied to any silicon series KD102, KDYuZ, KD503, KD510, KD521, KD522; bipolar transistor - KT3107 with any letter index. Instead of a field-effect transistor KP501A, KP501B or its functional analogue, the K1014KT1 chip, is suitable. Microphone ВМ1 - electret, for example XF-18D. Switch SA1 - compact MTB-102, SMTS-102 or similar. In addition to that indicated in the diagram, you can use super-bright white LEDs ARL-5013UWC, ARL-5613UWW, green - ARL-5213PGC, red - ARL-5613URW or similar.

For power, you can use a 3R12G galvanic battery or a battery of three series-connected galvanic cells or batteries of AA or AAA sizes. In the stationary version, a mains power supply is suitable, preferably stabilized, with an output voltage of 5 V. In this case, a socket for connecting an external power supply must be installed on the device case. The current consumed by the device in standby mode (when the LED is off) does not exceed 0,25 mA. It remains operational when the supply voltage drops to 3 V, but depending on the type of LED, the brightness may decrease significantly.

Establishing a night light consists in setting the voltage on the microphone with a tuning resistor R1 in the range of 0,7 ... 1,3 V. Since the BM1 microphone has a built-in amplifier, by changing its DC mode, you can change the sensitivity. The required value of the current through the LED, and hence the brightness of its glow, is set by selecting the resistor R5.

Since the device responds to acoustic signals, the LED will periodically flash at a frequency of about 2 Hz during loud music. Therefore, a night light can serve as an indicator of exceeding the permissible noise level. In this case, the EL1 LED should use a red glow. An interesting application of the device can be found in various competitions, contests, where participants must turn on (and turn off) the LED with claps in their palms in two or three attempts. The winner is the one who manages to do it from the greatest distance. From the editor. It should be noted that in the extreme positions (see Fig. 1) of the resistor R1 slider, the sensitivity of the microphone drops sharply. To prevent this from happening during adjustment, it is necessary to install a resistor with a resistance of 5,1 ... 10 kOhm between the engine and the microphone.

Author: A. Oznobikhin, Irkutsk

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