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Company Logo NXP Semiconductors

  • AM Wireless Temperature Sensor

  • Created: Nov 26, 2014

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The wireless technology brings us so much convenience. It eliminates bulkiness of device that make things so handy and easily access. This design circuit features digitization using tiny configurable logic gates, which is a common requirement of wireless transmission.

Most of the sensors outputs analog signal in which in this circuit it is digitized and transmitted wirelessly using the 74AXP1G57 NXP configurable tiny logic gates. The ability of these gates to be configured, in order to work as inverting gates with Schmitt trigger inputs. It is used to build RC relaxation oscillators for both digitizing analog sensors and for producing the RF (Radio Frequency) signal required to transmit the sensor values wirelessly. The resistor and capacitor control the frequency of the oscillator; increasing the value of either R or C decreases the frequency of oscillation. Since the temperature sensor or a thermistor can be modeled as a variable resistor or a variable capacitor, the analogy of a relaxation oscillator with resistor and capacitor can be used to explain the logic based wireless temperature sensor. At a certain temperature, fixed output frequency is produced from AXP1G57 based relaxation oscillator. As the temperature changes the output frequency will also change as the resistance of relaxation oscillator will also change. The digitized output can be transmitted wirelessly by adding a capacitor and inductor at the output of AXP device. Similarly, AXP1G57 configured as an inverter with Schmitt trigger and connected to the second AXP1G57GM device, configured as a two input NAND gate can be used as an AM wireless temperature sensor. In this case, as the temperature changes the amplitude of output is modulated. Again by using an inductor and a capacitor at the output of AXP1G57, the modulated AM wave is transmitted.

This design is suitable for the development of portable devices and other products that requires excellent wireless circuitry. It is suitable for modification for more specific application and it can improve the output signal of different types of sensor.