Firefly on a two-color flashing LED. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting
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In recent years, light switches with built-in indicator lights have become fashionable and widely used, making it easy to find the switch in the dark. To add more variety to the world around you, you can make a very simple indicator for the switch on a two-color flashing LED. Its scheme is shown in Fig. one.
Ris.1
An excess of mains voltage extinguishes the resistor R2, a rectifier is assembled on the diode VD2. Capacitor C1 smooths out ripples, and the zener diode VD1 does not allow the voltage on this capacitor to exceed 5,6 V. To prevent the indicator from annoying with its blinking during daylight hours, a photorelay assembly is provided on the photoresistor R1, field effect transistor VT1, resistor R3 and capacitor C2.
When the photoresistor is illuminated, its resistance is small - approximately 30 kΩ. For this reason, the voltage between the gate and source of the transistor VT1 is less than the threshold and the transistor is closed, and the HL1 LED is off. In the dark, the resistance of the photoresistor increases to 1 ... 10 MΩ, and the voltage at the gate of the transistor VT1 also increases. When it exceeds the threshold, the transistor will open. The power supply voltage will be supplied to the LED, and it will flash red and green alternately at a frequency of 1,5 ... 4 Hz.
Resistor R4 is designed to reduce the brightness of flashes. In addition, as it turned out, it evens out the brightness of flashes of red and green colors. If flashes of maximum brightness are required, this resistor can be replaced with a jumper, since there are built-in current limiting circuits inside the blinking LED.
Fig. 2
"Firefly" can be mounted on a round fiberglass board, shown in fig. 2. It is easy to install in the light switch box. To protect the device parts and printed conductors from accidental contact with the metal box and the switch mounting elements, two round plates made of sheet insulating material 0,5 ... 1 mm thick (for example, fiberglass without foil) with a diameter slightly larger than the board can protect. In no case do not wrap the board with insulating tape, tape, paper. This will disrupt air circulation and cause overheating.
The SPS-1 photoresistor can be replaced with another small-sized photoresistor and even a phototransistor (for example, L-32P3C) or a photodiode (for example, FD265). The oxide capacitor C1 is an imported analogue of the domestic K50-35, the capacitor C2 is a small-sized ceramic or film capacitor. Instead of a 1N4006 diode, any of the KD209, KD410 series is suitable, and in addition to the KS156A zener diode, others at 5,6 V are also suitable for working in a firefly - KS456A, KS 156G, 1N4734A, BZX55C5V6, BZV55C5V6. The KP504G transistor can be replaced by any of the KP501, KP502, KP504, KP505, ZVN2120, BSS88 series. When replacing, take into account the differences in the pinout of these transistors.
If there is no flashing two-color LED SB3RG6SCECX, then you can install SB3YG6SCECY (yellow / green), SB3BG6SCECY (blue / green), SB3RB6SCECY (red / blue), DK5BR3SSC (red / blue) or DK5GR3SSC (red / green) - all of them in cases with a diameter 5 mm. Such LEDs are often found in children's toys. In extreme cases, a single-color flashing LED is also suitable.
Author: A. Butov, p. Kurba, Yaroslavl region; Publication: radioradar.net
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