Abstract
In order to avoid the digital humidity & temperature sensor SHTxx’s output values conversion consume many quantity of storage location, and spend more operation time, a group new type of conversion polynomials, and corresponding programming algorithm were deduced and tested. The polynomials are precise equivalent to the conversion formulas provided by the manufacturers, but contain only Binary fixed-point integer, fractional part, and 2N. Using fixed-point calculations and shift operations instead of floating-point calculations, the results of program code reduction amount of 60 percent, and computing speed faster nearly 4 times than the original algorithm are obtained. Furthermore, a kind of speedy and unified CRC algorithm for read-out data of the sensor is proposed. The novel programming algorithm makes the output conversion more simplified, so it could pave the way for the low-end embedded applications of SHTxx.
Highlights
SHTxx series is Switzerland SENSIRION’s produces of high integrated digital Humidity & Temperature Sensor, with high measurement precision, it can be widely applied to many domain such as HVAC (Heating Ventilation Air Conditioning), weather station, workshop humidity and temperature control, medical treatment, automobile and home appliance etc.SHTxx does not like the DS18B20 which directly outputs the Binary integer and decimal complement form of measurement data, but outputs unsigned binary integer: corresponding to the measuring temperature is -41.08°C, 14 bit output data is x000H; when 100°C, in between 371FH to 3720H
The SENSIRION’s datasheet has given the linearization conversion formulas for the humidity, and two fold line for the temperature to avoid square operators, it is at the cost of loss of accuracy, the converting errors is several times more than the sensor’s measurement error
-2E-8 in third item is changed to the fraction form, and the denominator can be transformed into two bytes binary integer multiply by 212, so these can be solved by Double-Byte fixed-point multiplication and division, and N times right shift operation to substitute for divide by 2N
Summary
SHTxx series is Switzerland SENSIRION’s produces of high integrated digital Humidity & Temperature Sensor, with high measurement precision (temperature 14 bit and Humidity 12 bit resolution ratio), it can be widely applied to many domain such as HVAC (Heating Ventilation Air Conditioning), weather station, workshop humidity and temperature control, medical treatment, automobile and home appliance etc. SHTxx does not like the DS18B20 which directly outputs the Binary integer and decimal complement form of measurement data, but outputs unsigned binary integer: corresponding to the measuring temperature is -41.08°C, 14 bit output data is x000H; when 100°C, in between 371FH to 3720H. Another not enough is that its output value and measured value don’t be the linear relationship. It is significant to research simple and accurate conversion algorithm for decreasing program code and speeding up the computing, so the SHTxx can be applied widely
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