Automotive probe-indicator with a resolution of 1 volt. Free Technical Library article

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Automotive probe-indicator with a resolution of 1 volt

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Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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To monitor the health of the vehicle's electrical equipment on the road, a voltage indicator within 12 ..._nm<11,5 V), or a malfunction of the voltage regulator (at U_nm>15B).

The simplest and most reliable way to control the voltage in the on-board network is with a six-level voltmeter proposed by O. Klevtsov in his article "On-board LED voltmeter" in Radio, 1998, No. 2, p. 54. I offer readers another version of a similar device that uses the threshold properties of a digital microcircuit. It uses a five-level LED voltage indication (see diagram in Fig. 1). The switching voltage of the elements DD1.1, DD1.4, DD2.1, DD2.3 is set by a selection of resistors R2-R6. Element DD1.4 switches when and „_И1 more than 11,5 V, DD2.3 - more than 13 V, DD2. 1 - more than 14 V, DD1.1 - more than 15 V.

Automotive probe-indicator with a resolution of 1 volt

When the voltage in the on-board network is below 11,5 V, the yellow HL2 LED is on, since the DD1.4 element will switch the DD1.3 element to a low level state with a high output level. The remaining LEDs will be turned off, since the output of the remaining elements is a single voltage, and the transistor VT2 is closed.

As soon as the voltage in the on-board network exceeds 11,5 V, the elements DD1.4 and DD1.3 will switch, the HL2 LED will turn off. The switched element DD1.2 will open the transistor VT2, which will apply voltage to the LEDs HL3-HL5. A low level at the output of the element DD2.4 will turn on the green LED HL5. With a further increase in on-board voltage, the HL4 and HL3 LEDs will alternately turn on, indicating voltage levels of 13 and 14V.

And finally, when the onboard voltage exceeds 15 V, the DD1.1 element will switch to the zero state - the "red" LED HL1 will turn on, indicating an emergency in the electrical system. At the same time, the element DD1.2 will switch and the transistor VT2 will close.

To establish the indicator, it is connected to the output of a DC source with a voltage varying within 10 ... 16 V. By changing and controlling it with an accurate voltmeter, resistors R3-R6 are selected to provide the indicated thresholds for switching on the HL1-HL5 LEDs.

Diode VD1 protects the device from erroneous connection in the wrong polarity.

All parts of the device are mounted on a printed circuit board made of one-sided foil fiberglass 1 mm thick. The board drawing is shown in fig. 2. After adjustment, the mounted board is fixed behind the front panel of the car so that the LEDs protrude out through the holes drilled in the panel. You can also arrange the device in the form of a pocket probe, which is convenient when troubleshooting the car's electrical system and monitoring voltage at various points. To do this, the parts are placed without a board in a tubular case of a suitable size, soldered with thin insulated conductors and filled with paraffin. LED lenses are brought out through holes drilled in the housing. An example of the placement of parts is shown in fig. 3; resistors and zener diode are not shown. A tubular sleeve is attached to the end, into which a pointed probe (positive terminal) is inserted during measurements. Negative output - a segment of a flexible conductor with an alligator clip at the end.

On fig. 4 shows a view of the probe placed in the case from the used felt-tip pen-marker.

Resistors MLT-0,125 are used in the indicator. capacitor C1 - K50-35, C2 - KM-5. Transistors can be any low power; zener diode VD2 - any with a stabilization voltage of 7 ... 10 V.

Those. those who believe that three indication levels are enough - less than 11,5 V, 11,5 ... 15 V and more than 15 V - can simplify the design of the indicator. In this case, the DD2 chip, the VT2 transistor and the HL3-HL5 LEDs become unnecessary. Instead of the transistor VT2 (more precisely, its emitter junction), a "green" LED is turned on, which will indicate the normal operation of the electrical equipment, and the resistance of the resistor R8 is reduced to 1 kOhm. The chain of resistors R3-R5 should be replaced with one, with a resistance of about 2 kOhm.

Author: I. Potachin, Fokino, Bryansk region; Publication: cxem.net

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