Micro-power sub-ultrasonic remote control lighting

Micro-power sub-ultrasonic remote control lighting

The micro-power remote control lighting introduced in this article is designed for disabled people with lower limb paralysis. It is simple and easy to make, low cost, high sensitivity and stable operation. The remote control signal transmitter of the remote control lamp is a small rubber airbag (available in the electronics market), which does not require electricity and is durable. At night, the disabled person only needs to pinch the airbag placed next to the pillow, and the indoor light will automatically light up; if he pinches it again, the light will automatically go out, which is very convenient to use. In addition, due to a series of power-saving measures taken in the circuit, when the light is not on, the standby working current of the lamp is only 180μA.

1. Circuit Working Principle

The remote control lamp is composed of voltage stabilization, remote control signal receiving and control circuits, and its circuit principle is shown in Figure 1.

In the figure, VD1, VT4, R10 and C5 form a high-efficiency micro-power voltage-stabilizing circuit. When the power is turned on, the 220V AC is half-wave rectified by VD1, reduced by R10 and limited by current, filtered by C5 and stabilized by VT4 be-junction to generate a stable DC voltage of about 7.5V for the entire circuit. VT4 is used here as a micro-power voltage-stabilizing tube. Compared with ordinary silicon voltage-stabilizing diodes, the voltage-stabilizing tube composed of a low-power silicon triode be-junction still has a good voltage-stabilizing effect even when working at a current of several microamperes (the voltage-stabilizing performance of ordinary silicon voltage-stabilizing diodes will be significantly deteriorated when working at such a low current). According to actual measurements, the stable voltage of the be-junction of the 9013 silicon triode is about 7.5V (related to its β value and manufacturer), and its working current (i.e., the reverse current flowing through the be-junction) remains basically unchanged even if it drops to a few microamperes. Due to the use of this voltage-stabilizing circuit for power supply, the standby working current of the entire circuit of the lamp is only 180μA.

VT1, VT2, L, C2 and other components form a high-gain frequency-selective amplifier. The frequency selection frequency is determined by L and C2, which is set at around 16kHz, which is very close to the frequency of the sub-ultrasonic remote control signal emitted by the airbag. IC is a CMOS dual D trigger, in which ICB is connected to a bistable circuit to control the conduction and cutoff of the unidirectional thyristor VS; ICa, R8 and C4 form a monostable circuit to shape the trigger pulse of the bistable circuit so that it can be reliably flipped. Usually, because the output terminal Q2 of ICb is at a low level and VS is cut off, the bulb HL will not light up.

At night, when the disabled need to turn on the light, they only need to pinch the airbag placed beside the pillow. The piezoelectric ceramic BC (here used as a sound-to-electric transducer) will receive the sub-ultrasonic remote control signal and convert it into a corresponding electrical signal and send it to the base of VT1. This signal is amplified by VT1 and VT2 and selected by L and C2, and then added to the base of VT3 through R6, so that VT3 in the cut-off state is instantly turned on. The trigger pulse output by its collector is shaped by ICa and becomes a trigger pulse with a steep edge and added to the CP2 end of ICb, so that it flips, and the output of Q2 end of ICb becomes high level, so VS is turned on and HL lights up. If the airbag is pinched again, the bistable circuit composed of ICb will flip due to being triggered again, and its Q2 end will become low level again, so that VS is cut off again and HL is extinguished. At this time, the whole circuit enters the micro-power waiting state.

2. Selection of components

Transistors VT1 and VT2 use 9014, and the β value of VT1 is required to be around 120, and the β value of VT2 is required to be around 350; VT3 uses 9015, and the β value is required to be greater than 250, and Iceo <0.1μA; VT4 uses 9013, and the β value is required to be around 130. VS uses BT169D type unidirectional low-power thyristor, and its trigger current is required to be less than 30μA. L can use a color-coded inductor with a DC resistance of less than 25Ω. C2 uses a polyester capacitor. Resistors R1~R10 are all 1/4W metal film resistors. BC should use the piezoelectric ceramic sheet used in sub-ultrasonic remote control switches. If it is not available, it can also be removed from some waste sub-ultrasonic remote control switches. HL should use an incandescent bulb below 60W. The airbag can be purchased from the electronics market. There are no special requirements for other components.

3. Debugging and production

As long as the components are selected according to the values ​​in the figure and the welding is correct, the remote control lamp can work normally without debugging. Its remote control distance can reach 10m. If this value cannot be reached, the depth of the small plug on the top of the airbag can be appropriately adjusted to make the frequency of the sub-ultrasonic remote control signal emitted by the airbag as consistent as possible with the frequency selection frequency of the receiving circuit. If the anti-interference ability is not strong enough, the resistance value of R4 can be appropriately increased or the capacity of C3 can be reduced.'

The appearance of the remote control lamp is shown in Figure 2. For the convenience of production, all components are made into a printed board and then installed in a white wall switch shell. During production, the piezoelectric ceramic sheet BC can be glued to the inner side of the wall switch shell with a universal glue, and some sound-permeable holes should be opened in front of it. After the production is completed as shown in Figure 2, the wall switch is fixed to a suitable position on the wall and connected to the incandescent lamp HL for use.

Since the remote control light is directly connected to 220V AC power, attention should be paid to safety during debugging and production to avoid electric shock.