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Batteries Not Included

GardenState
The first Embedded Systems Conference in Chicago (well, truth be told, Rosemont,  IL, which is just off the runway at O’Hare) was “co-located” this week with the somewhat larger Sensors Expo & Conference. The notion of co-location doesn’t always succeed—you would probably not want to be co-located in the same house with your neighbor, for example—but since sensors play a key role in embedded technology, especially in the automotive and industrial space, the combination worked well.
 
 
Attending both events gave one the opportunity to see similar technology patterns emerging in parallel. One common theme between MCU and sensor development, wireless sensors in particular, is the ongoing march toward ultra low power consumption. On the sensor side much progress has been made via improved circuitry and better signaling protocols to reduce energy consumption and prolong battery life.
 
 
The next step, closer the most would imagine, is to get rid of the battery altogether, relying for power on energy harvesting of ambient energy sources such as piezoelectric vibration, thermal, and solar energy. Transducers that create electricity from physical sources such as temperature differentials (thermoelectric generators), mechanical vibration (piezoelectric) and light (photovoltaic devices) are becoming viable sources of power for wireless sensing devices.
 
 

For example, at the Sensors Expo Powercast demonstrated a battery-free wireless sensor module powered by RF energy. The module provides temperature and humidity data to an access point along with the received signal strength and the ID number of the Powercaster transmitter from which it is receiving power. The company’s P1110 and P2110 Powerharvester Receivers  are capable of converting radio waves in the range of 850-950 MHz into DC power.  The demonstration sensor module used the P2110 Powerharvester receiver to store the received energy into a capacitor, and then performed a voltage boost to supply the module components will a regulated voltage.  Both the P1110 and P2110 enable an MCU to determine the signal strength of the received power, as well as to recover low-rate data encoded in the power broadcasted from the power transmitter.

 

 

If there isn’t an ambient RF source handy, you can also use a piezoelectric transducer attached to a vibrating mechanical source such as an HVAC duct or a window pane. Recently, Linear Technology’s introduced its LTC3588-1 piezoelectric energy-harvesting solution,  a device that can extract energy from almost any source of mechanical vibration or strain.

 

The LTC3588-1 integrates a low-loss full-wave bridge rectifier with an efficient buck converter. An ultralow quiescent current undervoltage lockout mode with a wide hysteresis window allows charge to accumulate on an input capacitor until the buck converter can efficiently transfer a portion of the stored charge to the output. In regulation, the LTC3588-1 enters a sleep state in which both input and output quiescent currents are minimal. The buck converter turns on and off as needed to maintain regulation.

 

 

Four output voltages, 1.8V, 2.5V, 3.3V and 3.6V, are pin selectable with up to 100mA of continuous output current; however, the output capacitor may be sized to service a higher output current burst. An input protective shunt set at 20V enables greater energy storage for a given amount of input capacitance.