Image Processing Reference
In-Depth Information
Wireless Vibration Monitoring Case Example
In the reference case, a black box communication solution was chosen, i.e., DUST Networks
SmartMesh XD chip. It is actually a complete SoC solution, where both the hardware and software
are hidden within the box. here is very limited control over how the communication is managed,
e.g., the protocol, wake-up scheme for radio, etc.
A small portion of the communications interface resides outside the SoC component, possibly
in the application, which handles packet preparation. his makes the integration between the SoC
andtherestofthesystemverytight.
headvantageisthatminimaldesigneforthastobespentonthecommunicationsprotocol.
But, the drawback is that debugging is very difficult because of the limited control and debugging
support available through the provided interface.
27.9 Power Supply
The power supply is a central part of the WSN device; it is the “motor” that provides power to
the various parts of the system. This motor can take many different shapes and forms and conse-
quently provide varying degree of performance and lifetime. The general requirement is an energy
autonomous system that requires little or no manual intervention (charging, maintenance, battery
change, etc.) to operate throughout its target lifetime. his requires a thorough requirements analysis
of the power demands and a clever design that is able to bridge power outages and handle variations
in power consumption.
27.9.1 Requirements
27.9.1.1 Power Demands
Before deciding on a suitable power supply technology, the power demands of the system need to be
clearly deined. he power demand is directly related to the sleep-wake-up scheme of the device as
discussed in Section .. It can thus be divided into a constant “housekeeping” part corresponding
to the losses associated with the operation of sensor and electronics, and a time-varying power level
thatisrelatedtothecommunication.
27.9.1.2 Energy Buffer
Regardlessoftheenergysourceemployed,aninternalenergystorageiscommonlyusedinlow-power
WSNs. his internal buffer enables the power supply to provide an even supply level in spite of a vary-
ing power inflow (e.g., when employing an energy-scavenging solution), and to handle intermittent
peak consumptions (e.g., during start-up sequences). If an alternative power supply with a discon-
tinuous power inflow is used, the buffer size will mainly be determined by the time characteristics of
the power source. As such, the charging and discharging of the internal buffer needs to be accounted
for in the sleep-wake-up scheme of the device.
Wireless Vibration Monitoring Case Example
As the wireless vibration sensor is rated for temperatures well below zero, the battery voltage level
might decrease too much with the load. This in combination with the current limiting resistor
(IS adaptation) might result in a situation where we do not have enough voltage to operate the
radio (especially during start-up). To solve this, a capacitor bank was connected across the power
supply, which stores just enough energy required for short radio transmissions. See Figure .
for an overview of the battery design.
