SMD500 Datasheet, PDF (6/10 Pages) List of Unclassifed Manufacturers – Altimeter / Barometer Module ultra low power, low voltage

read uncompensat ed t emperat ure value
UT
exam p l e:
UT = 32864
C code function:
read uncompensat ed pressure value
UP
UP = 37342
calculat e t emperat ure
X1 = UT * 64385 / 2¹⁶ - (AC6 + 1415) * 8
X2 = (X1 * X1) / 2¹³
Y2 = (-4955 * X2) / 2¹³
X3 = (X2 * X1) / 2¹⁶
Y3 = (11611 * X3) / 2¹²
X4 = (X2 * X2) / 2¹⁶
Y4 = (-12166 * X4) / 2¹⁴
B5 = (AC5 + 496)*(2 * X1 + Y2 + Y3 + Y4)/ 2¹⁰
T = (B5 + 8) / 2⁴
calculat e coefficient s B3 and B4
B6 = B5 - 4000
X1 = (B2 * (B6 * B6 / 2¹² )) / 2¹¹
X2 = (AC2 - 457) * B6 / 2⁹
X3 = ((X1 + X2) + 2) / 2²
B3 = (AC1 - 2218) * 2 + X3
Y1 = (AC3 -1984) * B6 / 2¹⁰
Y2 = (B1 * (B6 * B6 / 2¹² )) / 2¹⁶
Y3 = ((Y1 + Y2) + 2) / 2²
B4 = (AC4 + 8808) * (Y3 + 32768) / 2¹⁴
X1 =
X2 =
Y2 =
X3 =
Y3 =
X4 =
Y4 =
B5 =
T=
=
4310
2267
-1372
149
422
78
-58
4237
265
26.5 °C
SMD500_calt emperat ure
B6 =
X1 =
X2 =
X3 =
B3 =
Y1 =
Y2 =
Y3 =
B4 =
237
0
-103
-26
11704
-415
1
-103
26781
SMD500_calB3B4
calculat e t rue pressure
p = ((UP - B3) * 100000) / B4
X1 = (p / 2⁸ ) * (p / 2⁸ )
X1 = (X1 * 3038) / 2¹⁶
X2 = (- 7357 * p) / 2¹⁶
p = p + (X1 + X2 + 3791) / 2⁴
display t emperat ure and pressure value
p=
X1 =
X1 =
X2 =
p=
=
95732
139129
6449
-10747
95700
957.00 hPa
SM D5 0 0 _c al p r essur e
Figure 4: Calculation temperature and pressure
The calculated true pressure is given in steps of 1 Pa and the temperature in steps of 0.1 °C.
3.3 Calculating altitude
With the calculated pressure p and the pressure at sea level p₀ e.g. 1013.25 hPa, the altitude in meters can be calculated with the
international barometric formula using:
altitude
= 44330
*
⎜⎛
⎜1
⎜⎜⎝
-
⎜⎜⎝⎛
p
p₀
1
⎟⎟⎠⎞ ^5.255
⎟⎞
⎟
⎟⎟⎠
∆p = 1 hPa corresponds to 8.43 m at sea level
6
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