Inductance proximity sensing with a single chip

Inductance proximity sensors can be used for non-contact detection of metals near LC sensors. These inductive sensing solutions enable task counting on existing inspection and factory assembly lines without being affected by non-inductive materials such as oil, water, dirt or dust. Perhaps one thing you don't realize is that the ultra-low-power MSP430FR6989 microcontroller (MCU) includes an integrated extended scan interface (ESI) peripheral (which can be used as an analog front end (AFE)) for direct connection to PCB coils. To achieve low cost and low power inductor proximity sensing.

LC sensors are commonly used in applications related to inductive sensing. After charging the capacitor with a short pulse, the LC sensor oscillates and the signal voltage drop is attenuated. Metal objects can attenuate the signal faster due to energy absorption caused by eddy currents in the metal. This faster attenuation allows the detection of metals near the sensor. This TI Design reference design TIDM-INDUCTIVEPROX demonstrates the hardware and software needed to take advantage of advanced ESI peripherals in a single-chip inductive proximity sensing implementation. This solution is also very energy efficient and requires only a few microamps of current. In this configuration, an integrated analog front end is used to simulate LC sensors, sense signal levels, and convert them to digital displays. This data is then stored in a preprocessing component and analyzed using a processing state machine.

This type of application can be implemented on an MSP-EXP430FR6989 MCU LaunchPadTM development kit by connecting an LC sensor to the ESI pin on the bottom of the board. The TI Design reference design mentioned above shows multiple LC sensor variables to demonstrate the effect on the output signal frequency and attenuation rate.

If an application requires a higher resolution (that is, to determine the exact distance of the metal compared to whether the metal is detected within the range), an inductor-to-digital converter such as the LDC1612 or LDC1101 can be added to the system. With this two-chip solution, the MSP430FR6989 microcontroller can be used to keep the system in standby until metal is detected and then wake up the high-resolution LDC IC to capture accurate measurements.