Simplify Your Next Position Sensor Design with Microchip’s Plug and Play Sensor Library

Inductive position sensors are a new magnetic technology that provide an accurate position sensor without the need for a magnet. In this case, the sensor is just tracing on a printed circuit board (PCB) that generates a magnetic field and then measures the location of the field disturbance by a metal target. No magnet is needed. The advantage is more accurate position sensing, for both linear and rotational sensors, robust immunity to stray magnetic fields and with Microchip’s latest library, a simple and robust implantation. With a simple three step process using the new Microchip Position Sensor Library, you can simply download your position sensor and start building your next design.   

• Step 1: Choose and download a sensor layout from the Position Sensor Library

• Step 2: Order the matching LX3302AQPW-EASY sensor IC

• Step 3: Build and run your system

Step 1: Download your PCB Sensor 

The sensor library has four general purpose inductive position sensors and more will be arriving soon. There are two rotary sensors and two linear sensors. The two rotary sensors can absolutely measure 360 electrical degrees and 180 degrees respectively and have sensor diameters of 30 mm and 18 mm respectively. The metal target can have an air gap as large as 8.5 mm for the 360-degree design and 2.5 mm for the smaller 180-degree design. These are great choices for any sensor that can be applied to the end of a shaft like a robust knob or encoder application. While the 180-degree sensor is limited to a 180-degree absolute angle measurement, with a microcontroller (MCU) to read the sensor output, this range can easily be extended to also measure 360-degrees, allowing a full 360-degree rotation operation as some applications require. 

The linear sensors library examples provide an absolute linear position of 100 mm and 50 mm with target air gaps of 3 mm and 5 mm. They will provide 12 bits of resolution over those ranges allowing you to maximize resolution for your application. For example, a sensor that requires 30 mm of travel could use both sensors but would be better served by using the 50 mm linear. For 30 mm of travel, the 50 mm sensor has twice the resolution of the 100 mm sensor and is a better choice for this application.      

After downloading the sensor layout, place the schematic and sensor PCB design “as-is” into your PCB project. Then attach your project’s 5v power to the Vin trace and the project’s grounds to the Gnd trace. The IC has three outputs that will output the angle or position as an analog 0-5v signal, a 1 kHz PWM signal and the Single Edge Nibble Transmission (SENT) protocol signal. Attach the one that can be used by your system MCUand you are all set.  Or if you want, you could attach to all three. These signals are all 5v tollerant signals, so care must be taken when interfacing with a 3.3v or lower microcontroller. If you have any questions, you can reference Microchip’s application note, LX3302A: Interfacing with 5v and 3.3v Powered Microcontrollers. Do you want to try the SENT protocol, but don’t know how? Microchip’s LX3302A SENT Interface Microcontroller Code Example describes how to implement the powerful SENT protocol with MCU GPIO outputs.   

The shape of the metal target for each sensor is also provided. This design is provided both as a PCB layout, .DXF or .STEP file, allowing you to choose how you want to build your target. Microchip often has the target made from PCB material, since 1 oz copper thickness of a target is all that is needed for the sensor to work. However, if you need a metal target to attach the main sensor enclosure, .STEP and .DXF files are also provided to interface with modern mechanical CAD systems.  

Step 2: Order the LX3302AQPW-EASY  

The LX3302AQPW-EASY is a special version of the LX3302A that has its configuration memory (EEPROM) values pre-programmed to work with the sensor library and has its output configured as described in step 1. The advantage is that no modification of the IC’s internal configuration is required. You don’t even have to read the datasheet. It’s ready to plug and play.  

Step 3: Build and Run Your System

The next step is to build the project and solder the LX3302AQPW-EASY onto the PCB. Apply power to the IC and place the target above the PCB near the given usable range and start reading the outputs by your MCU and interface of choice. The accuracy of this signal will be similar to the uncalibrated results shown on the sensor specification document provided in the sensor download files.  

The optimum accuracy is achieved by calibrating your sensor using the calibration files for the sensor and code examples from Microchip. In the sensor’s download zip file are two calibration files than can be used with a small linearization routine in your MCU. The more points the better, so if you have the memory, use the file with more calibration points. The linearization routine can be downloaded from the LX3302A product page with the link titled, External Linearization of LX3302AQPW-EASY sensors using a PIC18F Microcontroller. After reading the sensor by your MCU, call the linearization routine using the calibration points provided to get accurate calibrated sensor accuracy. In addition to the code, the link also provides a full example of how it can be used with the PIC18F family of MCUs.   

Visit and download your next position sensor here, order your IC and get started using this innovative technology. In addition to the library, full kits and programmers are also available and we encourage you to try both.    

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