Temperature sensors are one of the most important kinds of physical sensors, because many different processes (in everyday life as well) are regulated by temperature. Besides, the temperature measurement allows indirect determination of other physical parameters, such as matter flow rate, fluid level, etc. Typically, sensors convert the measured physical value into an analog signal, and temperature sensors are no exception here. For processing by the CPU or computer, the analog temperature signal must be converted into a digital form. For such a conversion expensive analog-todigital converters (ADCs) are commonly used.
The purpose of this project is to develop and present a simplified technique for direct conversion of the analog signal from a temperature sensor into a digital signal with proportional frequency using GreenPAK™. Subsequently, the frequency of a digital signal that varies depending on temperature can then be more easily measured with a fairly high accuracy and then converted to the required units of measurement. Such direct transformation is interesting in the first place by the fact that there is no need for the use of expensive analog-to-digital converters. Also, digital signal transmission is more reliable than analog.
Below we described steps needed to understand how the temperature to frequency converter has been programmed. However, if you just want to get the result of programming, download GreenPAK software to view the already completed GreenPAK Design File. Plug the GreenPAK Development Kit to your computer and hit the program to design the converter.
Design and Circuit Analysis
Different types of temperature sensors and their signal processing circuits can be used depending on specific requirements, primarily in temperature range, and accuracy. The most widely used are NTC thermistors, which reduce the value of their electrical resistance with increasing temperature (see Figure 1). They have a significantly higher temperature coefficient of resistance compared to metal resistive sensors (RTDs) and they cost much less. The main disadvantage of thermistors is their nonlinear dependence of the characteristic "resistance vs. temperature". In our case, this does not play a significant role since during conversion, there is an exact correspondence of the frequency to thermistor resistance, and therefore, the temperature.Read more »