Timer in the wiper control unit. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Timer in the wiper control unit. Encyclopedia of radio electronics and electrical engineering

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

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Timing units of various windshield wiper control devices, as a rule, are built on unijunction transistors or their analogues, the main disadvantage of which is unreliable locking with a low resistance of the charging resistor. The use of the integrated timer KR1006VI1 in the time-setting unit in combination with a powerful output transistor eliminates this drawback.

The device ensures continuous operation of the wiper for approximately 3 seconds (two brush cycles). The pause between cycles can be adjusted within 0,5..20 s. The windshield wiper is controlled by a variable resistor installed on the dashboard of the car.

Schematic diagram of the timer is shown in Fig.1

Timer in wiper control unit

The time-setting node is assembled on the DA1 timer. It generates a pulse signal with independent adjustment of pulse duration (wiper motor running) and pause (off). The duration of the pause is regulated by the resistor R5, and the duration of the pulse (the number of double strokes of the brushes) - by the trimming resistor R3.

When turned on (closing the contacts of the switch SF1, combined with resistor R5), capacitor C3 begins to charge through resistor R1. Immediately after the supply voltage is applied, the output of the DA1 timer is set to a high voltage level. Transistors VT1, VT2 are open, and the power supply voltage is supplied to the wiper motor. After charging the capacitor C1 to a voltage of 2/3 Upit at the output of the timer DA1, the voltage decreases to almost zero, and the transistors VT1, VT2 close. But the wiper motor will work until the brushes return to their original position (until the contacts of the limit switch in the mechanism open).

After switching the timer, the capacitor C1 begins to discharge through the resistors R4, R5. If pauses lasting more than 20 s are needed, then a resistor R5 or capacitor C1 of a larger rating is installed.

The device uses MLT resistors, a variable resistor R5 - SPZ-12k or SPZ-30k. The quality of the capacitor C1 (K50-16) determines the stability of the time characteristics of the wiper cycle. The KT961A transistor can be replaced with KT815A-KT815G, KT646A; transistor KT805BM - on KT805AM, KT891A, KT819B-KT819G. Transistor VT2 is mounted on a plate heat sink with dimensions of 50x30x3 mm.

Literature

Radio No. 12, 1988, p.25

See other articles Section Automobile. Electronic devices.

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