Automobile tachometer on the K1003PP1 chip. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automobile. Speedometers and tachometers

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Most modern cars are equipped with tachometers, which facilitate the correct choice of gear, which extends the life of the engine. If your car does not have such a device, then it can be made according to the proposed description.

The tachometer circuit is shown in fig. 1. Its main feature is the use of the K1003PP1 chip, designed to control a linear scale of 12 LEDs. In the standard version described in [1], the microcircuit provides the formation of a column of luminous LEDs, the length of which is proportional to the input voltage.

The signal, the frequency of which is proportional to the speed of the engine crankshaft, is taken from the contacts of the chopper or from the amplifier-shaper of the Hall sensor and is fed through the voltage divider R1R2 to the input of the Schmitt trigger DD1.1. The purpose of the trigger and capacitor C3 is to suppress bounce pulses at the output of the chopper, high-voltage surges on the ignition coil winding and bring the signal to standard CMOS logic levels with normal steepness of the fronts.

Rice. 1 Tachometer circuit

The output signal of the Schmitt trigger starts the waiting multivibrator on the DD2 chip. In the main position of the switch SA1 "6000", the duration of the pulses generated by the waiting multivibrator is 2,5 ms. At a rotation speed of 6000 rpm, the pulse frequency for a four-cylinder engine is 200 Hz, the repetition period is 5 ms, the duty cycle is 2. The R12C6 integrating circuit averages these pulses, and the average voltage across capacitor C6 is about 3 V. This voltage is supplied to the output . 17 (UBX) DD2 chips. At a voltage of 3 V applied to the pin. 3 (UB) of this microcircuit and determining the indication scale, all 12 LEDs HL1 ... HL12 are turned on, forming a luminous column.

At lower engine speeds, the duty cycle of the pulses at the output of DD1 increases, the average voltage across the capacitor C6 decreases in proportion to the speed, and the height of the column becomes smaller. When the engine is stopped, none of the LEDs are lit. "Price of division" of the LED scale - 500 rpm.

It is advisable to install LEDs of a different glow color. For example, if 2000 ... .4000 rpm correspond to optimal engine operation, the HL1 ... HL3 LEDs can be used yellow or orange ("switch to a lower gear"), HL4 ... HL8 - green ("normal"), HL9...HL12 - red ("shift to a higher gear").

To adjust the idle speed, the switch must be set to the "1200" position. In this case, the duration of the generated pulses will increase by 5 times and will be 12,5 ms, and the "division" of the scale will be 100 rpm.

Microcircuits DD1 and DD2 of the tachometer are fed through an integrated voltage regulator DA1. Capacitors C1 and C2 ensure the stability of the stabilizer.

The current through the LEDs connected to the DA2 chip is determined by the voltage at its pin. 2. In the daytime, when the instrument panel lights are off, there is a log at the inputs of the DD1.2 element. 0, at the output - voltage 6 V, on pin. 2 DA2 - about 0,85 V, which sets the current to 25 mA through each LED. In the evening, when the backlight is turned on, the voltage at the pin. 2 is reduced to 0,4 V, which reduces the current through the LEDs to 8 mA and, accordingly, their brightness.

A drawing of the printed circuit board of the tachometer is shown in fig. 2. The design used constant resistors MLT, tuning SPZ-19a. Capacitor C5 type K73-17 for a voltage of 250 V, C6 - K50-16, the rest - KM-5 and KM-6. Chip DA1 - any voltage regulator for 6 V, for example, KR1157EN6 with any letter index, KR142EN5B (G), KR1180EN6, 78L06, 7806 [2]. The K561TL1 chip can be replaced with KR1561TL1, CD4093, CD4093B, and K1003PP1 with UAA180 or A277.

Orange glow LEDs - AL307MM (yellow ones usually glow weaker than others), green ones with increased brightness - AL307NM6, red ones - AL307BM. The leads of the LEDs are bent at an angle of 90°, and their axes are directed parallel to the printed circuit board. The size of the LEDs is reduced to 5 mm with a file.

Switch SA1 - any small-sized toggle switch, it should be installed in close proximity to the printed circuit board.

The unused inputs of the DD1 and DD2 microcircuits are connected either to a common wire or to a +6 V circuit.

Setting up the tachometer is quite simple. First, the SA1 switch is set to the "6000" position, positive polarity pulses with an amplitude of 12 V with a frequency of 200 Hz and a duty cycle close to 2 are applied to the tachometer input to simulate connection to a breaker. The entire LED column is lit with a trimmer resistor R9. If necessary, select the resistance of the resistor R8. Then the same operation is performed for the position SA1 "1200" with an input pulse frequency of 40 Hz.

Next, they check whether, when a voltage of 12 V is applied to the left terminal of the resistor R3, the brightness of the LEDs decreases. If desired, it can be installed by selecting resistors R5-R7.

The LEDs can be arranged in a circular arc. In this case, the glow of one LED from the chain may turn out to be more effective. To ensure this mode of turning on the LEDs, their anodes should be disconnected from the outputs of the DA2 chip and connected to the power output (pin 18).

Literature:

1. I. V. Novachenko, V. M. Petukhov, I. P. Bludov, A. V. Yurovsky. Microcircuits for household radio equipment. Directory. - M.: Radio and communication, 1989.
2. Integrated circuits. Microcircuits for linear power supplies and their application. - DOJA, 1996.

Author: Sergey Khristoforov, editor@dian.ru; Publication: radioradar.net

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