Traditional Chinese Practical Automatic distress call: Circuit Design, Parts List & Workshop Prototype Guide

Premium 11,198 credits (=$111.98) · Priced by article length · permanent access after unlock · 1 $ = 100 credits

Automatic callerIf a patient with a heart attack suddenly faints, his life will be in danger if he is not rescued in time. Now we would like to introduce an automatic rescue device to readers. Once a patient wearing a call for help faints, the call for help can automatically send out a call for help signal. In urgent need, it can also be manually controlled to send out a call for help signal. People who hear the signal can come to help.How it works:People's bodies move to a greater or lesser extent when walking or working. When the wearer faints or stops moving completely for 5 minutes, the rescue device can automatically send out a cry for help.The rescue device is composed of a signal source, a sensor circuit, an amplifier, an alarm power supply control circuit and an acoustic alarm circuit. The circuit schematic is shown in Figure 198-1. The four operational amplifiers A1, A2, A3, and A4 in the circuit are LM324 quad operational amplifiers. A1 and A2 respectively form two Wien bridge oscillators as signal sources, and are coupled to the alarm and sensor circuits using C11 and C6. A bridge inductive sensor circuit is composed of RP2, R9, R8, L and C7 as bridge arms, and L is an inductive vibration sensor (self-made).When the human body moves, the oscillator of the inductor L vibrates, causing the inductance to continuously change. As a result, the bridge loses balance and generates a modulation signal that changes with the inductance. This signal is directly sent to the amplifier, first amplified by the differential amplifier composed of A3, and then detected and filtered by CD1 and C8 to form a positive fluctuation signal. In order to obtain a stable control signal, the fluctuation signal that changes with the inductance is coupled to the comparator A4 through C9, and compared with a +3.2V voltage, a stable +5.6V voltage is obtained. This voltage turns off the transistors VT1 and VT2 of the switching circuit. Since VT2 is cut off, the power supply to the alarm circuit is cut off. The comparator and switch circuit constitute the alarm power supply control circuit.When the human body stops moving, the bridge of the sensor circuit is in a balanced state, the differential amplifier A3 has no fluctuation signal output, and the comparator A4 generates a stable voltage of +0.4V. After the comparator reverses, due to the delay effect of R16 and C10, the voltage of C10 drops to +3.5V after 5 seconds, causing the Zener diode 2CW9 to conduct, and VT1 and VT2 also conduct, thus turning on the power supply of the alarm circuit and sending out an alarm signal.The alarm circuit is composed of audio integrated block TB4100. The 1KHz audio signal generated by A1 is coupled to TB4100 through capacitor C11 for audio power amplification, so that the speaker generates a sound signal that is enough to be heard 20m away. If people working in dangerous situations use this rescue device, they can also change the acoustic alarm to a radio alarm, so that the monitoring personnel can receive the signal from a distance.Component selection:The LM324 and TB4100 (ie LA4100) integrated blocks are selected in the caller, mainly for the convenience of adjustment, reduction in size and cost. If it is made with discrete components, the price will be higher and it will be more difficult to adjust. VT1 and VT2 use 3AX61 tubes, VD1 uses 2CP9, and VD2 uses 2CW9. Inductive vibration sensors are key components. However, since the linearity and sensitivity requirements for this component are not high, it can be made by yourself.Installation and production:The sensor consists of an inductor L, an oscillator P and a small box M, as shown in Figure 198-2. On the gable-shaped high-frequency magnetic core with dimensions of 6×10×20 (mm), directly wind 365 …

Sign in to unlock

Login / Register

One-time payment per article, billed in credits (1 $ = 100 credits). You will review the invoice and the non-refundable digital-asset policy before anything is charged. The PDF is generated on demand and embeds a licensing watermark.