Ramasadaya nodes control the wipers, as a rule built on unijunction transistors or their analogues, main the lack of which is unreliable locking at low impedance charger the resistor. Application in breathalyser node of the integral timer in KRUI the output transistor can eliminate this drawback.
The device provides continuous operation of the wiper for about 3 with (two cycles of operation of the brushes). Pause between cycles can be adjusted within 0,5..20 s. the Wiper control using a variable resistor, installed on the car dashboard.
Schematic diagram of the timer shown in Fig.1
The timing Assembly is built on the timer DA1. It generates a pulse signal with independent adjustment of the pulse duration (the motor wiper works) and pause (off). The duration of the pause regulate resistor R5, and the pulse width (the number of double strokes of brushes) - a trimming resistor R3.
When you turn on (the closure of the contacts of the switch SF1, combined with resistor R5) through the resistor R3 starts charging the capacitor C1. Immediately after submission the voltage on the timer output DA1 is set to a high level voltage. Transistors VT1, VT2 opened, and the wiper motor receives a supply voltage. After charging of the capacitor C1 until the voltage 2/3 U pit at the output of the timer DA1 voltage is reduced almost to zero, and transistors VT1, VT2 are closed. But the wiper motor will work to return the brush to its original position (not yet open contacts end switch in the mechanism).
After switching the timer capacitor C1 begins to discharge through resistors R4, R5. If necessary pauses of more than 20, then set resistor R5 capacitor C1 or higher amperage.
In the device used resistors MLT, variable resistor R5 - SDR-12K or SDR-30K. The quality of the capacitor C1 (K50-16) depends on the stability of time characteristics of the cycle of operation of the wiper. Transistor CTA can be replaced by CTA-CTG, CTA; transistor KTM - CHAM, CTA, CTB-CTG. The transistor VT2 is mounted on a heat sink plate dimensions 50x30x3 mm.
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