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[FAQ] Sensors in Washers and Dryers

Other Parts Discussed in Thread: DRV5032, TMAG5124, TMAG5110, TMAG5111, DRV5013, TMAG5273, FDC1004

Question: Can home appliances – specifically washing machines and dryers – use position sensors such as Hall-effect, Inductive or capacitive sensors as controls and to detect movement or exact position of moving parts?

 Answer: Yes, in many cases, including appliances, monitors and controls that have traditionally been supported by mechanical switches and sensor assemblies can indeed be implemented with Hall-effect, inductive or capacitive sensors. The remainder of this note provides two examples where these sensors are used for washing machines and dryers.


Use case #1: Open/Close detection

In the image below, the Hall-effect position sensor (red) is located near the door latch receptacle, and a magnet (blue) is positioned on the washer door near the latch. The goal of this implementation is to detect an open door in the event of a latch failure. Please see the tables below for device recommendations and links to application notes and other documents.

Recommended Products:

Device Data Sheet Description System-level Benefits
DRV5032 DRV5032.pdf Ultra-Low-Power Digital-Switch Hall Effect Sensor The DRV5032 is designed for the most compact applications and is offered in multiple magnetic thresholds.
TMAG5124 TMAG5124.pdf Two-wire (current output), high-voltage (up to 38 V), high-precision switch for remote sensing The TMAG5124 device is a high-precision Hall effect sensor that offers a 2-wire interface designed for industrial designs. Different product variants enable selection of different levels of magnetic sensitivity.

Related documents:

Innovative Sensing Solutions for Home Appliances App Note Provides an overview of position-sensing applications in appliances, and gives an example of open/close detection using the DRV5032 & TMAG5124.
Transition Detection Using Hall-Effect Sensors App Note Explores open/close detection using a laptop as an example.

Use case #2: Drum speed detection

An effective and inexpensive way to monitor the drum position and speed is to use magnets and a Hall-effect latch to monitor the magnets’ movements. In this application, a magnet attached to the drum will pass by the Hall sensor and trigger the latch. The micro-controller will then record the event and reset the latch. This approach can provide precise knowledge of the drum position and speed, and avoids the wear-and-tear of mechanical assemblies that rely pressure or event-driven actuation. The table below shows device recommendations and links to device data sheets.

Recommended Products:

Device Data Sheet Description System-level Benefits
TMAG5110.pdf Dual-Channel, High-Sensitivity, Hall-Effect Latch The TMAG5110/1 are dual, 2D Hall-effect latches operating from a 2.5 V to 38 V power supply and are optimized for applications leveraging rotating magnets. Integrating two sensors and two separate signal chains the TMAG511x offers two independent digital outputs giving speed and direction calculation (TMAG5111) or giving directly the digital output of each independent latches (TMAG5110). This high level of integration allows the use of a single TMAG511x device instead of two separate latches
DRV5013 DRV5013.pdf High voltage (up to 38-V), high bandwidth (30-kHz) Hall effect latch The DRV5013 device is a chopper-stabilized Hall effect sensor that offers a magnetic sensing solution with superior sensitivity stability over temperature and integrated protection features.

Use case #3: Washing machine water level

Two effective ways of monitoring water level are offered by Hall sensing and capacitive sensing devices. The Hall-sensing approach utilizes a magnet and Hall device working together via the familiar float-and-armature assembly used in many day to dat products. The advantage of a Hall device is that it avoids the use of a potentiometer that can degrade over time.  A capacitive sensor measures the liquid levels by monitoring the change in electrode capacitance as the liquid rises and falls. The electrodes in contact with the liquid can often be small, simple strips of conductive material. The advantage of capacitive sensing is that it has no moving parts, so mechanical wear-and-tear is avoided. Please see the tables below for device recommendations and links to application notes and other documents.

Recommended Products

Device Data Sheet Description System-level Benefits
TMAG5273 TMAG5273.pdf Low-Power Linear 3D Hall-Effect Sensor with I2C Interface The TMAG5273 is a low-power linear 3D Hall-effect sensor designed for a wide range of industrial applications, integrating three independent Hall-effect sensors in the X, Y, and Z axes as well as a precision analog signal chain along and an integrated 12-bit ADC that digitizes the measured analog magnetic field values.
FDC1004 FDC1004.pdf 4-Channel Capacitance-to-Digital Converter for Capacitive Sensing Solutions The FDC1004 is a high-resolution, 4-channel capacitance-to-digital converter with integrated sensor shield drivers, which can reduce EMI interference and help focus the sensing direction of a capacitive sensor.

Related Documents:

Title Description Summary
What solutions do you recommend for measuring liquid via level sensing and other delivery methods in Medical applications? FAQ While this FAQ emphasizes medical applications, it also provides an overview of Hall and capacitive sensing solutions to the problem of liquid-level detection.
Center stage with Hall sensors Blog This blog covers a wide range of potential applications for magnetic sensing using Hall devices, including liquid-level sensing.
Capacitive Sensing: Direct vs Remote Liquid-Level Sensing Performance Analysis App Note This application note highlights the system differences and performance of direct and remote sensing to provide guidance in how capacitive-based liquid-level sensing is affected.
FDC1004 Capacitive Sensing FAQs FAQ This FAQ addresses some commonly asked questions, and gives a comprehensive list of app notes and blogs for the FDC1004.

Use case #4: Buttons and dials

Settings and controls for Washing machines and dryers are frequently implemented with dials and push-buttons, which in turn use potentiometers and mechanical push-buttons. These two functions can be realized with Hall-effect devices (for the dial) and inductive sensors for the push-buttons. The advantage offered by the Hall device for the rotary dial is that it avoids the mechanical interaction of the knob shaft and a potentiometer, thereby avoiding mechanical wear. The advantage offered by inductive sensors for a push-button is that its single moving part – a conductive dome - is not subjected to abrasion, and thereby avoids wear-and-tear, which ultimately results in mechanical failure. Push-buttons using inductive sensors can also be easily sealed to prevent external contaminants. Please see the tables below for device recommendations and links to application notes and other documents.

Recommended Products

Device Data Sheet Description System-level Benefits
LDC3114 LDC3114.pdf 4-channel inductance-to-digital converter for low-power proximity and touch-button sensing

Device analog & digital features coupled with internal algorithms make this a best-in-class device for push-button applications. The raw data output supports estimation of the button-press force, which could be used to expand a button’s function beyond the usual ON/OFF behavior.

LDC2112.pdf 2 or 4- Inductive Touch Solution for Low-Power HMI Button Applications Device analog & digital features coupled with internal algorithms make this a best-in-class device for push-button applications. The

Related documents:

Title Description Summary
Replacing Mechanical Switches With Inductive Sensors App brief A brief survey of the parameters and features that make LDCs a great way to implement push-button functions for many applications.
Design Considerations for Inductive Touch Buttons for the Human-to-Machine Interface App brief A brief survey of the major care-abouts for inductive touch buttons.
LDC-HALL-HMI-EVM: Evaluation module for inductive touch and magnetic dial contactless user-interface design Application EVM with GUI and user’s guide This EVM features eight push-buttons based on inductive sensors and a dial based on Hall sensor technology. The EVM + GUI provide a convenient platform for experimentation and the user’s guide provides details on the EVM design and functions.
Illuminated Inductive Touch Buttons FAQ How would you implement an inductive touch button that needs to be illuminated?
This FAQ gives an overview of how to add illumination to an inductive touch button.

Additional Tools and Resources: