You know how hard the driver of the car staying awake during long trips at night and at dawn. But any weakening of attention of the driver can turn into a disaster!
The figure shows a schematic diagram of an apparatus that automatically includes the car's horn at the time when the driver began to feel drowsy and relaxed his fingers, gripping the steering wheel control. Power audio signal enough to "shake up" the driver and make it stronger to hold the wheel, or, if it does not help to attract the attention of drivers of other vehicles.
This device is easy. The "heart" of the device oscillator is executed according to the scheme "capacitive treatacne" on the transistor T1. The base of transistor T1 through a capacitor C3 are connected to the metallic rim And reinforced around the perimeter of the steering wheel. When the driver tightly grips the steering wheel, due to the large capacity of the body of the driver relative to the vehicle's mass base of the transistor T1 is shunted by the capacitor C3, resulting in the generation does not occur.
If the driver will relax your fingers, shunt capacitance is reduced and the generator is energized at a frequency of about 300 kHz. The voltage of this frequency with the collector of the transistor T1 flows through the emitter follower transistor T2 to the input of the detector, made of the diodes D1 and D2. The rectified voltage diodes opens the transistors T3 and T4 electronic relay, causing the relay P1, closing its contacts in the circuit for the alarm.
Adjustment of the device is to install the required sensitivity of the oscillator. This is done by means of the potentiometer R4. In addition, the potentiometer R5 regulate the current of the electronic relay.
Powered device from the on-Board network voltage of +12 V. the Coil L1 is wound on a ferrite core, the inductance is 1 MH.
The transistors T1-T3 may be the type KT315 with any letter index, T4 KT361. Diodes D1 and D2 - DV - DA, D3 - XA, D4 - DB. Turnips R1 - resistance of the coil is not less than 120 Ohm.
Literature
Publication: N. Bolshakov, rf.atnn.ru