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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Ignition system malfunction indicator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Ignition

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The proposed indicator notifies the driver about the status of the vehicle's ignition system. The device is made on an accessible element base, can be replicated by beginning radio amateurs and practically does not require adjustment.

Every car enthusiast has probably found himself in a situation where the car engine would not start. And there can be only two main reasons for this, when the starter cranks the engine and this engine is gasoline - a malfunction of the ignition system or a malfunction of the fuel system. If you immediately correctly determine the cause of the malfunction, then the car’s downtime on the road will be significantly reduced and it will be possible to do without a tow truck, because the reason may turn out to be very simple, for example, poor contact of a high-voltage wire.

The described device is intended for cars in which there is no operational monitoring of the serviceability of the ignition system. If the ignition is working properly, the indicator does not show itself; if there is a malfunction, the lamp starts flashing. It uses a standard minimum fuel level lamp, which, after installing the indicator, performs two functions - it shows the minimum fuel level and signals a malfunction of the ignition system. The use of a standard lamp made it possible not to interfere with the design of the front panel of the car. The disadvantage of this solution is the inability to control the state of the ignition system at a minimum fuel level, but the lack of fuel in itself may be the reason that the engine does not start.

If desired, you can use another lamp located on the front panel of the car, or make a portable version of the indicator and connect it only when problems arise.

Ignition fault indicator
Rice. 1 (click to enlarge)

The indicator diagram is shown in Fig. 1. The input assembly is assembled on elements C1, R1, R2, VD1, generating control pulses for the operation of the indicator; on the trigger DD1.1 - a one-shot device with an output pulse duration of 15 ms; on the logical element DD2.1 and the trigger DD1.2 - a restartable one-shot device that controls the operation of a multivibrator assembled on the logical elements DD2.2, DD2.3. Element DD2.4 is turned on by the inverter, and the switch on transistor VT1 supplies voltage to the indicator lamp HL1.

After turning on the ignition, +12 V supply voltage is supplied to the indicator. Integrated voltage stabilizer DA1 reduces the supply voltage to 9 V. When the engine is cranked with the starter, the voltage in the vehicle's on-board network decreases significantly and depends on the condition of the battery, oil viscosity, ambient temperature, etc. Stabilizer DA1 keeps the supply voltage constant, which means The parameters of the one-shot pulses are also constant both when the engine is cranked by the starter and when the engine is running. After supplying the supply voltage, a low logical level appears at the output (pin 12) of the DD1.1 trigger, and a high logic level appears at the output of the DD2.1 inverter. Through resistor R4, capacitor C4 is charged. The voltage on C4, having reached the switching threshold of trigger DD1.2, transfers it to the single state.

A low logic level at the inverse output (pin 2) of trigger DD1.2 allows the multivibrator to operate. The HL1 indicator lamp begins to blink, and its serviceability is checked. The lamp switching frequency is determined by the time constant of circuit R6C5.

When the car engine is running and the ignition system is working properly, high-voltage pulses periodically appear in the spark plug wires. From the sensor, these pulses arrive through the input node C1, R1, R2, VD1 to input C (pin 11) of the trigger DD1.1, which generates pulses with a duration of 15 ms from them. Zener diode VD1 protects this input from possible overvoltage. When the first pulse arrives, a low logic level appears at the output of inverter DD2.1 and capacitor C4 is quickly discharged through diode VD2. Trigger DD1.2 switches, and a high logic level appears at its inverse output (pin 2). This level prohibits the operation of the multivibrator on elements DD2.2, DD2.3. Indicator lamp HL1 does not light up. The time constant of the R4C4 circuit is selected so that each subsequent low-level pulse coming from the output of the inverter DD2.1 manages to discharge the capacitor even before the trigger DD1.2 switches at the lowest engine speed.

If a malfunction occurs, the pulses from the sensor disappear and capacitor C4 is charged through resistor R4. Trigger DD1.2 switches, and a low logic level appears at its inverse output (pin 2), allowing the multivibrator to operate on DD2.2, DD2.3. The HL1 indicator light starts flashing. Thus, the condition of the lamp monitors the overall serviceability of the ignition system. A malfunction in the form of a lack of spark formation in one cylinder is easily determined by engine vibration and exhaust sound, and in this case the engine, as a rule, starts, but the car “does not pull.”

Ignition fault indicator
Fig. 2

The indicator is assembled on a printed circuit board made of one-sided foil-coated fiberglass laminate 1 mm thick. The printed circuit board drawing and arrangement of elements are shown in Fig. 2, and the appearance of the assembled indicator is in Fig. 3.

Ignition fault indicator
Fig. 3

A piece of insulated single-core copper wire, several turns of which are wound around a high-voltage spark plug wire, is used as a high-voltage pulse sensor. The number of turns for different cars can be different and depends on the type of ignition, the highest voltage wire, the gap in the spark plugs, etc. In any case, the selection of the number of turns must begin with the minimum and be limited to one in which cranking the engine with the starter does not cause flashes indicator lamp. In my case, on the AZLK 214122 “Svyatogor” car with a homemade thyristor ignition, it was five turns. The wire is wound turn to turn and covered with electrical tape on top. In the case of a portable version, you can use a sensor, the design of which was described in “Radio”, 2004, No. 1, p. 45, 46 in the article by N. Zaets “Car strobe from a laser pointer.”

Ignition fault indicator
Fig. 4

After assembling the indicator, before installing it on the car, it is advisable to check the functionality of the indicator using a short pulse generator, a circuit diagram of which is shown in Fig. 4. The signal from the generator is supplied directly to input C (pin 11) of the trigger DD1.1. By rotating the knob of the variable resistor r2 (Fig. 4), check the functionality of the indicator. If the R4C4 circuit does not operate correctly, the resistance of the resistor R4 or the capacitance of the capacitor C4 changes. Having installed the indicator on the car, it is necessary, as mentioned above, to select the minimum required number of turns of wire for the sensor. The sensor is connected to the board with a shielded wire about 0,5 m long, the shielded braid is connected to the common wire on the board side.

The DD1 chip can be replaced with HEF4013B, KR1561TM2; DD2 - on HEF400B, KR1561LE5.

We can replace the BZX55B9V1 zener diode with any small-sized one with a stabilization voltage of 9 V. The KD522B diode is any of the KD522 series. Capacitor C1 - KT-2, it can be replaced with a ceramic capacitor for a voltage of 500 V or higher, the rest are imported ceramic ones; C5 - oxide imported. We will replace the VT1 KT3117B transistor, for example, with an imported 2N2222.

The device is located in the engine compartment of the car in the area where the fuse box is mounted. Since devices placed on a car are susceptible to moisture and vibration, after installation the board is covered with two or three layers of waterproof varnish. It wouldn’t hurt to cover it on the parts side with silicone sealant.

Author: P.Yudin

See other articles Section Automobile. Ignition.

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