Discover a simple method for converting an analog temperature sensor signal to a digital frequency.



Temperature sensors are one of the most essential types of physical sensors since temperature regulates many different processes (including those in everyday life). Furthermore,temperature measurements enable the estimation of other physical properties such as matter flow rate,fluid level,and so on. Sensors,including temperature sensors,typically convert the recorded physical value into an analog signal. The analog temperature signal must be converted to digital before being processed by the CPU or computer. Analog-to-digital converters (ADCs) are often employed for such conversions.



The goal of this project is to use GreenPAK to build and propose a simplified technique for converting an analog signal from a temperature sensor to a digital signal with proportional frequency. Following that,the frequency of a digital signal that varies with temperature can be measured more readily and accurately and then translated to the needed units of measurement. Such direct transformation is appealing in the first place because it eliminates the need for costly analog-to-digital converters. Furthermore,digital signal transmission is more dependable than analog signal transmission.



Below we described steps needed to understand how the solution has been programmed to create the temperature-to-frequency converter. However,if you just want to get the result of programming,download&nbsp;<a href="https://www.dialog-semiconductor.com/greenpak-designer-software" target="_blank" rel="noreferrer noopener">GreenPAK Designer software</a>&nbsp;to view the already completed&nbsp;<a href="https://www.dialog-semiconductor.com/sites/default/files/an-cm-xxx_temperature_to_frequency_conversion_using_greenpak_0.zip" target="_blank" rel="noreferrer noopener">GreenPAK Design file</a>. Plug the&nbsp;<a href="https://www.dialog-semiconductor.com/products/greenpak/slg4dvkadv#tab-field_tab_content_order" target="_blank" rel="noreferrer noopener">GreenPAK Development Kit</a>&nbsp;into your computer and hit the program to design the device.



<h2>Design and Circuit Analysis</h2>



Depending on specific needs,such as temperature range and precision,many types of temperature sensors and associated signal processing<a href="https://eduengteam.com/2022/03/electronic-circuits-active-vs-passive.html" data-type="post" data-id="4402"> circuits</a> can be utilized. NTC thermistors are the most common,as they reduce the value of their electrical resistance as the temperature rises (see Figure 1). When compared to metal resistive sensors (RTDs),they have a substantially higher temperature coefficient of resistance and cost significantly less. The fundamental disadvantage of thermistors is that their characteristic "resistance vs. temperature" is nonlinear. In our situation,this is irrelevant because the frequency and thermistor resistance,and thus the temperature,are the same during conversion.



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/XhnRpxM/XhnRpxM9HfOjyuGRP9uQXBVgpEN7T5cbEMDermGB.jpg" alt="Figure 1 Thermistor Resistance vs Temperature plot.jpg"/></figure>



Figure 1 shows the graphical dependence of thermistor resistance vs temperature (which were taken from manufacturer datasheets). For our design,we used two similar NTC thermistors with a typical resistance of 10 kOhm at 25°C.



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/izxiRga/izxiRgaIBIpHl9cXOWasmJy7urHkChq8tLn536Ul.jpg" alt="Table 1 Type of Used Thermistors.jpg"/></figure>



The use of the thermistor R1 together with the capacitor C1 in the frequency-setting R1C1-circuit of the generator,as part of a classic ring oscillator using three "NAND" logic elements,is the basic idea of the direct transformation of the temperature signal into the output digital signal of a proportional frequency. R1C1's time constant is affected by temperature because the resistance of the thermistor changes as the temperature changes.



The frequency of the output digital signal can be calculated using the following formula (1):



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/KWdcTA5/KWdcTA5O5wcvWIzEEzgdnEd3KFJ1DsKcXOHBdjDh.jpg" alt="Figure 2 Schematic of Active Sensor.jpg"/></figure>



A resistor R2 is usually added to this sort of oscillator to limit the current through the input diodes and lessen the burden on the circuit's input parts. If R2's resistance value is substantially lower than R1,it has no effect on the generation frequency.



Consequently,based on the&nbsp;<a href="https://www.dialog-semiconductor.com/products/greenpak/slg46108" target="_blank" rel="noreferrer noopener">GreenPAK SLG46108V</a>,two variants of the temperature to frequency converter were constructed (see Figure 5). The application circuit of these sensors is presented in Figure 3.



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/HINuup2/HINuup2IzzVvLGxlm2acT7WvmGKj6ll6W5etvZnb.jpg" alt="Figure 3 Electrical Circuit of Active Sensors (for GreenPAK SLG46108V) .jpg"/></figure>



As previously said,the design is relatively simple: it consists of a chain of three NAND components that create a ring oscillator (see Figures 4 and 2) with one digital input (PIN#3) and two digital outputs (PIN#6 and PIN#8) for external circuitry connection.



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/DCdzVda/DCdzVdazh0vXnEaqGAdpopGz57EJ72j9bAGfeHjG.jpg" alt="Figure 4 GreenPAK Designer Schematic .jpg"/></figure>



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/DCdzVda/DCdzVdazh0vXnEaqGAdpopGz57EJ72j9bAGfeHjG.jpg" alt="Figure 4 GreenPAK Designer Schematic .jpg"/></figure>



Figure 5 Photo shows the active temperature sensors (a one cent coin is for scale).



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/4PautfI/4PautfIzQUqgrsMkMO2b1Y6Eaof9bAjeDsysxGcT.jpg" alt="Figure 5 Photo of Active Temperature Sensors .jpg"/></figure>



The correct function of these active temperature sensors was evaluated through measurements. Our temperature sensor was put in a temperature-controlled chamber with a temperature precision of 0.5 degrees Celsius. The output digital signal's frequency was recorded,and the findings are shown in Figure 6.



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/6mW9VGQ/6mW9VGQcFf2r61K3Md23I15DDOkUPoE7AnJZ2cC5.jpg" alt="Figure 6 Comparison of Calculated vs. Measured Frequency .jpg"/></figure>



The frequency measurements (green and blue triangles) almost exactly match the theoretical values (black and red lines) according to formula (1),as can be seen in the graph. As a result,this method for translating temperature to frequency is accurate. Also,a third active temperature sensor was built (see Figure 7) to demonstrate the possibility of simple processing with visible temperature indication. Using the&nbsp;<a href="https://www.dialog-semiconductor.com/products/greenpak/slg46620" target="_blank" rel="noreferrer noopener">GreenPAK SLG46620V</a>,which contains 10 delay elements,we have built ten frequency detectors (see Figure 9),each of which is configured to detect a signal of one particular frequency.



In this way,we constructed a simple thermometer with ten customizable points of indication.



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/VGZlaFw/VGZlaFwSif3AyybX51Olm0THw26PlLqnnLz3abr5.jpg" alt="Figure 7 Photo of Active Temperature Sensor with LED Indicators.jpg"/></figure>



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/XfKUf5W/XfKUf5W3seGg8XJe1bVY0dle9rDVa7lFwn6lSGZg.jpg" alt="Figure 8 Electrical Circuit of Active Sensor (for GreenPAK SLG46620V).jpg"/></figure>



Figure 8 depicts the active sensor's top level schematic,which includes display indicators for ten temperature values. This extra feature is useful since it allows you to visually estimate temperature values without having to analyze the generated digital signal independently.



<figure class="wp-block-image is-style-default"><img src="https://maker.pro/storage/KeDIwIl/KeDIwIldBsGig0hdw5xpWA3FtBMuhYQfrzBsvz7W.jpg" alt="Figure 9 GreenPAK Designer Schematic View of SLG46620V.jpg"/></figure>



<h2>Conclusions</h2>



Using GreenPAK devices from Dialog,we proposed a method for transforming a temperature sensor analog signal into a frequency modulated digital signal in this project. The use of thermistors in conjunction with GreenPAK enables for repeatable readings without the use of costly analog-to-digital converters,as well as the elimination of the need to measure analog signals. As illustrated in the prototype samples built and evaluated,GreenPAK is the best choice for the development of this type of configurable sensor.



GreenPAK includes a significant variety of functional elements and circuit blocks that are required to build various circuit solutions,reducing the amount of external components in the final application circuit. GreenPAK's low power consumption,small chip size,and inexpensive cost are all advantages of using it as the main controller in many circuit designs.

Temperature to frequency conversion using the GreenPAK device.

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Temperature to frequency conversion using the GreenPAK device.

Temperature to frequency conversion using the GreenPAK device.

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