WEATHER_VANE

Published:2009/7/15 0:22:00 Author:Jessie | From:SeekIC

IC1-a and IC1-b form an astable oscillator in which IC1-a produces a positive pulse width that is proportional to the resistance of the segmented potentiometer, R1. The negative pulse width, deter-mined by IC1-b, is fixed. The third section, IC1-c, is triggered by the falling edge of IC1-b. Its pulse width is set by potentiometer R7 so that it is exactly equal to the width of the IC1-a's pulse when the vane is at zero resistance. Potentiometer R8 and IC1-d make up the frequency reference. An astable oscillator (formed out of IC1-d and its surrounding components) provides a clock signal to IC2, a 555 timer IC. The RESET pulse from IC1-c starts to count at zero, and the LATCH pulse from IC1-a freezes the instantaneous reading in the timer. So, U2 counts the time between the falling edge of IC1-a and the falling edge of IC1-c, which is determined by the position of the vane. The timer can feed its digital output to the three-digit display circuit of your choosing (such as an MC4511 display driver). To adjust the circuit, rotate RI (the transducer) to its zero-resistance position (North) and adjust R7 until the readout is zero. Second, rotate R1 to its maximum-resistance position and adjust R8 until the readout is 350. That will give, theoretically, readings between zero and 350 in 10- degree increments as the vane is rotated.



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