Wiatr

Z Wiki.2o.pl
Informacje podstawowe
Programy obsługujące: OWFS
Adaptery obsługujące: DS9097, DS9490
Measuring Wind Direction on the 1-Wire Net

The original 1-Wire weather station used DS2401s to label each of the eight magnetic reed switches in its wind direction sensor, as shown in Figure 4. A single DS2450 quad ADC can perform the same function with five resistors. As the wind rotates the wind vane, a magnet mounted on a tracking rotor opens and closes one (or two) of the reed switches. When a reed switch closes, it changes the voltages seen at the input pins of U1, the DS2450. For example, if the magnet is in a position to close S1 (north), the voltage seen on pin 7 changes from VCC to 1/2VCC, or approximately from 5V to 2.5V. Since all 16 wind vane positions produce unique 4-bit signals from the ADC, it is only necessary to indicate north, or specify which direction the wind vane is currently pointing to initialize the sensor.

DS2450-wiatr.gif

Because two reed switches are closed when the magnet is midway between them, just eight reed switches indicate 16 compass points. Referring to the schematic and position 2 in Table 1, which lists the voltages seen at the ADC inputs for all 16 cardinal points. Observe that when S1 and S2 are closed 3.3V is applied to ADC inputs B and C. This occurs because the parallel combination of pullup resistors R2 and R3 act as a single resistor half their value connected in series with R1 to form a voltage divider with 0.66VCC across R1. Note that this condition occurs twice more at switch positions 4 and 16 generating 3.3V at those cardinal points also.

Cardinal

Points

Voltage Input

at D(V)

Voltage Input

at C(V)

Voltage Input

at B(V)

Voltage Input

at A(V)
1
5
2.5
5
5
2
5
3.3
3.3
5
3
5
5
2.5
5
4
5
5
3.3
3.3
5
5
5
5
2.5
6
0
5
5
2.5
7
0
5
5
5
8
0
0
5
5
9
5
0
5
5
10
5
0
0
5
11
5
5
0
5
12
5
5
0
0
13
5
5
5
0
14
2.5
5
5
0
15
2.5
5
5
5
16
3.3
3.3
5
5

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