In today’s washing machines, especially high-end units, several sensors provide real-time monitoring and feedback to shorten or improve certain functions. In addition to the latest touch screen inputs discussed in Pt 1 of this blog, other sensors include:
- Rotor position sensor
- Water level
- Dirt sensor
- Photoelectric sensor
- Pressure sensor
- Vibration sensor
To select the appropriate microcontroller (MCU), Renesas identifies the differences between sensing on a high-end versus an entry-level washing machine. The low-end MCU handles temperature sensors for both the water and motor safety and the Hall effect sensor input for rotor position as well as a water line, final temperature and lid sensors. In contrast, the high-end MCU deals with these same sensors and adds a weight sensor.
One sensor supplier, TE Connectivity, offers several different types of sensors for home appliances, especially those for washing machines and dryers. Specific sensors can measure temperature, pressure, vibration, proximity and force.
While a pressure sensor can monitor water level, a force sensor measures the payload weight at the beginning of the wash cycle. A proximity sensor verifies that the door is closed and latched before start-up. For imbalance detection in washing machines, TE Connectivity provides vibration sensing with piezoelectric film technology. Its piezo film sensors are also used for control buttons in small appliance applications. In the dryer portion of laundry room sensing, a humidity sensor can monitor process humidity and stop the dryer when clothes are dry instead of running longer and consuming more power.
Another measurement that can provide useful information is a water flow measurement. This can be accomplished using a Hall effect sensor on a vane-type flow sensor.
Perhaps the simplest measurement is detecting that the door is open or closed. Reed switches are often used for this function.