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issue: July 2006 APPLIANCE Magazine

Sensors and MCUs
A Low-Power Way to Staunch the Flow


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by David Simpson, Contributing Editor

Water leaks from appliances in homes and businesses can be a serious problem, wasting water and, in severe cases, creating costly overflow damage.

Stopping water leakage and overflow is the goal of the H2ORB. The device is currently available for toilets, while the developer, AquaOne (Westminster, California, U.S.) plans versions for washers and other appliances. By incorporating Texas Instruments (Dallas, Texas, U.S.) ultra-low power MSP430 microcontrollers, AquaOne has been able to include a 5-year battery life in the compact design.

AquaOne Technologies Inc. is addressing the problem with a line of microprocessor-controlled water leakage and overflow monitoring systems. The first system, for toilets, is now on the market, with a washing machine monitor to follow by the end of 2006. A little further down the road are monitors for refrigerator icemakers, dishwashers and water heaters.
The “brains” of the H2ORB control units and sensors are Texas Instruments Inc. 16-bit MSP430 MCUs. One reason for the selection is the chips’ ultra-low power usage. Coupled with this, AquaOne created designs that allow 5-year operation from the control units’ standard coin cell batteries. Remote sensor battery life, on average, is 5 years. The control unit is designed for easy battery replacement by the owner/user.
The system uses proprietary RFID (radio frequency identification) technology from TI to allow continuous communication between the control unit and wireless remote sensors. Because the control unit is looking for specific RFID signals, it will not respond to a signal from a sensor on a nearby toilet.
The control unit uses TI’s MSP430F413 MCU, a member of what TI calls the industry’s lowest-power MSP430 MCU platform. The control unit includes a proprietary TI-RFID device to monitor inputs from the external tank and bowl sensors. The MCU, with integrated 8 KB of flash memory and 96-segment LCD driver, has a real-time clock standby power requirement of only 0.7 microamps. It can wake up from sleep mode to highest processing speed in an industry-best 6 microseconds.
“There is no need for the system to detect water leakage every microsecond,” points out Juan Alvarez, TI’s worldwide MSP430 marketing manager. “What the system needs to do is to stay in standby as long as it can without using the CPU. When the system wakes up, it should do so as fast as possible, sense any leakage or overflow, and if none, return to standby right away. With its low standby power and quick power up, the MSP430 family is ideal for this application.”
Each remote sensor includes an MS430F2101 MCU and a TI-RFid transponder. The tank sensor detects faults such as a slow leak or a stuck open flapper, while the bowl sensor detects when the water level reaches imminent overflow. Each sensor wirelessly signals the main unit when a fault is detected. The main unit will then react according to the fault and a user-defined preference. An actuator powered by the H2ORB button battery closes a valve to shut off water flow.
Besides low power usage, says Alvarez, the chips have a high level of peripheral integration. “We have been able to embed high-level analog and digital peripherals onto the chip. This makes it a more cost-effective solution,” he says.
A previous AquaOne design used wired bowl and tank sensors and required battery replacement after just 12 months. “The MSP430 MCU platform and RFID technology helped us implement a wireless system that lasts five times longer, is smaller and has more programmable features than any competitive system available,” observes Richard Quintana, AquaOne CEO.
“We addressed toilets first since there are some 1.2 billion in homes and businesses in the U.S. alone,” adds Brian Reel, AquaOne’s director of sales and marketing. “Number two on the insurance lists for creating water damage claims are washers. That’s why we developed a washer monitor, which we plan to release in the fourth quarter. Our basic approach is to retrofit wireless designs with the washers. However, we can also work with OEMs to incorporate our technology directly into their appliances.”
The washer monitor design uses flow management detection in conjunction with the appliance’s solenoid valve. The monitor will look at the expected water flow, and shut off the water supply if flow is too high or if there is flow and the washer is in the “off” mode. A design advantage with washers is that the control unit will be larger, and thus easier to produce, than the 3-inch H2ORB.

 

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