Alarm for emergency oil pressure reduction in a car. Free Technical Library article

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Oil pressure alarm in a car

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The proposed oil pressure alarm is intended for installation in Moskvich vehicles, where there is only a pressure gauge. The signaling device can also be installed on cars of other models.

As you know, when oil leaks from the system or there is no oil pressure, the engine of any car fails very quickly. To prevent engine failure, the driver must be informed by an attention-grabbing signal immediately in the event of an accident in the lubrication system. To date, not all cars have such a device, and the pressure gauges are not operational in this regard.

A characteristic feature of the proposed device (Fig. 1), assembled on six microcircuits, is that the driver controls its good condition before leaving when starting the engine. If the lubrication system is in good condition, then when the ignition is turned on, the VD2 LED should flash at a frequency of 1 ... 2 Hz, and when the engine is started, the flashing stops. Flashing of the LED when the engine is running indicates an emergency condition of the lubrication system (oil leakage from the system, failure of the oil pump, etc.). The LED is mounted on the instrument panel in close proximity to the oil pressure gauge.

Alarm for emergency oil pressure reduction in a car. Oil pressure alarm circuit diagram

The operation of the device is based on the dependence of the frequency of closing the contacts of the oil pressure sensor on the value of the oil pressure in the system. On fig. 2 shows timing diagrams of sensor contact vibration measured by an oscilloscope at the sensor contact.

Alarm for emergency oil pressure reduction in a car. Timing diagrams of sensor contact vibration

The operation of the device is as follows. Pulses from the oil pressure sensor (DMD) are fed to the input of the DD2 microcircuit, which acts as a galvanic isolation between the sensor contacts and the oil pressure alarm. Galvanic isolation is necessary due to the difference in the supply voltage of the microcircuits and the voltage on the DMD. The inverted DMD pulses from pin 10 of the DD2 chip are fed to the reset counter DD3 and the input of the divider by 16 (DD4).

The counting input of the counter DD3 receives the output signal of the generator, assembled on the elements DD1.1, DD1.2, DD1,3. The generator generates a frequency in the range of 500...1000 Hz. Thus, the pulses from the generator fill the counter, and the pulses coming from the DMD reset it. From this it follows that the transfer pulses at the output 12 of the DD3 counter appear if the sensor generates pulses with a duration of about 100 ms (Fig. 2, a). When shorter pulses arrive at the R-input DD3 (the engine is running - Fig. 2, b), the counter does not have time to fill up to the end with the generator pulses and there is a logical 0 at its output.

Entering the C-input of the JK-flip-flop DD5.1, the transfer pulse causes this trigger to fire. At its output 9, the state of logic 1 is set, which allows the passage of pulses from pin 10 DD4 to input 3 of the DD6.1 chip. The frequency of receipt of these pulses is 1...2 Hz as a result of dividing by the counter DD4 of the frequency generated by the optoelectronic switch-inverter. On the diagram of Fig. 1, the division factor is set to 8. It can be changed and made equal to 2 or 4, for which you need to connect input 3 DD6.1 to pin 13 or 9 of the DD4 chip.

JK-trigger DD5.2 is designed to bring the JK-trigger DD5.1 to its original state. When a pulse arrives from the output of the divider DD4 (pin 12) to the C-input of the JK-flip-flop DD5.2, it is transferred to the state of logic 1 on the trailing edge of the pulse (logical 13 is set at the inverse output 0). The DD5.2 trigger is reset by logic 0 coming from pin 13 of the DD5.2 chip. At the same time, at the input 12 of the 2I-NOT DD1.4 chip, a logic 1 is set, which allows the signal to pass from the output 13 of the counter DD3 to the R-input of the JK flip-flop DD5.2. With the first pulse, the trigger is transferred to the zero state. Now both triggers are in the zero state, the JK-trigger DD5.1 is again ready to receive information on the C-input (pin 5). If the transfer pulses are not received at the C-input of DD5.1, then pulses are constantly received at the R-input of DD5.2 confirming its reset. As soon as the first transfer pulse sets the DD5.1 JK flip-flop to a single state, the signal passing to the R-input of the DD5.2 chip will be terminated by a logical 0 at pin 12 of the DD1.4 chip and the DD5.2 JK flip-flop will be ready to reset the JK- trigger DD5.1 with the next pulse arriving at the C-input (pin 1) from the output 12 of the divider DD4. Setting triggers to their initial state or setting confirmation occurs periodically every 16 pulses generated by the sensor. The device is reset also when power is applied, i.e. when the ignition is switched on.

The open-collector chip DD6.1 provides current flow through the VD2 LED when the JK-trigger DD5.1 is set to logic 1. If the LED glow is not enough, then you can install a miniature HCM 6,3x20 incandescent lamp instead, eliminating the resistor R5.

For power, you can use the simplest voltage regulator, made on the transistor VT1 (KT807A) and the zener diode VD1 (KS156A). To reduce interference in the power circuit, an L1 choke with an inductance of 30 mH is installed.

All microcircuits used in the device have a planar pinout. During installation, a universal board was used, designed to install microcircuits of the 133, 134 series. The wiring of the intercontact connections is carried out with an MGTF wire with a diameter of 0,12. Resistors Rl, R2, R3, R5 and capacitor C1 are installed on additional contact pads; contact pads of free microcircuit seats can be used. Similarly, you can install a voltage stabilizer.

As DD1, you can use 133LAZ or 106LAZ, DD3, DD4-133IE5, 133IE2 microcircuits, paying attention to the difference in microcircuit contact numbers. All resistors in the device are of the MLT type, capacitors C1 are of the KM-6 type, C2 are of the K50-6 type.

Setting the signaling device consists in setting the switching threshold of the optoelectronic inverter-switch DD2. As can be seen from fig. 2, when the voltage at the input DD2 is 4 V, the input current must be insufficient to switch the inverter DD2. At a voltage close to 12V, the optoelectronic inverter must switch reliably. The switching threshold is set by resistor R3, i.e., pulses should be obtained at pin 10 DD2 when DMD pulses arrive at input 6. Resistor R2 regulates the frequency of the pulse generator. It must be set so that when the engine is idling, the LED flashes, and with a slight increase in engine speed, the flashing stops. If this cannot be done with the help of resistor R2, then it is necessary to change the capacitance of the capacitor C1, and a decrease in capacitance leads to an increase in the pulse frequency of the generator.

The mounted board is placed in a metal screen of the appropriate size and installed in the car interior near the instrument panel. You can connect to the DMD at one of the contacts of the oil pressure indicator. The +12 V power supply must be after the ignition switch.

It should be noted that on different vehicles, the duration and frequency of the pulses generated by the DMD will differ from the frequency and duration of the pulses shown in Fig. 2, but this will not affect the operation due to the large difference in the specified pulse parameters when the engine is running and not running. The device is also uncritical to the temperature instability of the frequency of the pulse generator, the signaling device has proven itself well in operation.

Publication: cxem.net

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