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The Internet of Things holds great potential, and much has been written about the final applications and the possibilities – however one major factor of any device is how it will be powered. It’s all very well to have the latest sensors or interactive devices, if they don’t have a suitable power supply. It’s easy to consider a battery – however there’s many more options that can increase lifespan, reduce maintenance calls and therefore the running costs. Let’s review a few options that can provide a portable power supply for your IoT nodes where mains power or cabled-in power supplies are not available.

First, consider solar photovoltaic – a common choice for sensing, control or measurement devices that are located outdoors where sunlight is available, and that consume a relatively small amount of power. For a small, low-power embedded device that receives a reasonable amount of sun each day, a moderately small solar panel is perfectly capable of supplying sufficient power – on average – to run a small, basic wireless network node consisting of a microcontroller, some sensors and an embedded low-power Wi-Fi, Bluetooth or 802.15.4/ZigBee radio transceiver. However this is assuming that the overall system is designed for a reasonable degree of power efficiency.

However, solar power is intrinsically intermittent and is only available on average for a fraction of the day. To allow the system to have access to the current it needs to function when needed, solar-powered wireless devices almost always need to incorporate a small amount of energy storage in the form of a battery or supercapacitor in conjunction with the solar cell. Furthermore, solar cells or solar panels typically have a relatively low output voltage if a small number of cells are used, and their non-linear V-I curve makes it desirable to employ Maximum Power Point Tracking (MPPT) where practical.

This is necessary to keep the system operating near the maximum power point so that the limited energy available is harvested most efficiently. A solar power supply for a remote wireless system ideally tracks the maximum power point of the cell along the V-I curve and is able to charge a small battery or supercapacitor to fill in the demand when sufficient sunlight is not available.

As an example of a controller IC one may use for the power supply in a small solar powered system, the Linear Technology LTC3105 is a high efficiency step-up DC/DC converter that can operate from input voltages as low as 225 millivolts, with a built-in maximum power point controller (MPPC). As well as solar cells, this device is well suited to other low voltage, high impedance energy harvesting transducers such as thermoelectric generators and fuel cells.

Whilst it is not a true maximum power point tracker, the user-programmable maximum power point setting helps to optimise the efficiency of energy extraction from any energy source, such as a thermoelectric pile or a solar cell, where the voltage across the transducer may vary with changing environmental conditions as well as with the load current. The LTC3105 is capable of supplying 70 mA of output current at 3.3V from an input voltage of 1 volt – this is sufficient power to run a small, well designed basic sensor node consisting of a microcontroller, RF transceiver and a sensor or two.

Another type of power supply is known as energy harvesting, made possible by parts such as the Linear LTC3108, which is designed to accommodate energy harvesting from transducers with extremely low output voltages, as low as 20 millivolts. This makes it particularly well suited for use with thermopiles and thermoelectric generators which can generate a very low potential difference from a realistic temperature difference – a potentially convenient energy source for remote sensing in industrial automation or process monitoring in high-temperature systems where wired communications and power are not convenient.

Energy can also be derived from vibration, and using a part such as the Linear LTC3588 – a piezoelectric energy harvesting power supply controller which connects to a piezoelectric crystal to harvest mechanical energy in the form of vibrations from the ambient environment. This IC incorporates a low-loss, full-wave bridge rectifier and is capable of accommodating the rapidly changing AC voltage output and high source impedance of a piezoelectric crystal subject to mechanical stress and converting this energy into a DC current with relatively high efficiency.

Output voltage selections between 1.8V and 3.6V are available with a continuous output current capability of up to 100 milliamps, compatible with a range of modern power-efficient microcontrollers and RF mesh systems-on-chip.

An electromechanical energy harvester of this sort can be employed to provide a continuous source of a small amount of “free” energy for a small, efficient wireless network mote, particularly in applications such as vehicles and industrial machinery where plenty of vibrational energy is available to be harvested in the environment.

Finally, for some systems it is also practical to use just batteries – for example, lithium-ion, lithium-polymer or nickel-metal hydride batteries – and rely on user intervention to simply
recharge and replace the batteries where needed. The batteries may be left internally, inside the device, with the system being plugged into a power supply via a charging port
– perhaps using a low-power standard power-supplying interface such as USB – when the device requires a recharge, as opposed to the traditional method of removing and swapping the batteries.

In this sort of application, battery management and charging ICs such as the Microchip MCP73833 Li-polymer / Li-ion charge management controller can be of use to control the recharge of a Li-ion cell, as can buck/boost converters such as the Texas Instruments TPS63031. A buck/boost converter like this allows a regulated output voltage to be generated from input voltages both higher and lower than the desired output voltage – an output of 500mA at 3.3V, in this case, from an input voltage anywhere from 2.4 to 5.5 volts. This allows a battery such as a two-cell NiMH, three-cell NiMH, or single-cell Li-ion / Li-polymer to be used efficiently and charged and discharged across the entire usable part of its discharge curve without hitting the minimum input voltage of a LDO or buck regulator.

No matter what your device or where it will be located, finding an appropriate source of power is possible, and easier than you realise. It just takes a little research and a team of dedicated engineers with the experience and knowledge to understand your requirements. Here at the LX Group we have the experience and team to make things happen. With our experience with connected devices, embedded and wireless hardware/software design, and ability to transfer ideas from the whiteboard to the white box – we can partner with you for your success.

We can create or tailor just about anything from a wireless temperature sensor to a complete Internet-enabled system for you – within your required time-frame and your budget. For more information or a confidential discussion about your ideas and how we can help bring them to life – click here to contact us, or telephone 1800 810 124.

LX is an award-winning electronics design company based in Sydney, Australia. LX services include full turnkey design, electronics, hardware, software and firmware design. LX specialises in embedded systems and wireless technologies design. https://lx-group.com.au

Published by LX Pty Ltd for itself and the LX Group of companies, including LX Design House, LX Solutions and LX Consulting, LX Innovations.

Recently an increasing number of networked devices are finding their way into consumer, industrial and medical applications. Such networks often employ distributed nodes which cannot practically be connected to the power grid – through design or through necessity. Therefore powering such devices can possibly be a challenge – due to the costs of either running from battery or solar power, sending technicians for maintenance visits to replace batteries – or having to install one’s own power network for the IoT system.

This is where energy efficiency is key – by using highly energy-efficient design practices in both the hardware and software levels, the power requirements can usually be reduced significantly. In doing so the power supply paradigm can be altered to one of lower cost and higher efficiency. Especially for remote or portable devices that use RF/microcontroller chipsets – the smaller the power requirement the better.

High-power and efficient wireless network nodes can be engineered using modern RF microcontroller system-on-chip devices, activating sensors and peripheral hardware devices only when they are required, and then putting them into low-power sleep modes when not in use. Similarly, the RF transceiver can be switched into a very-low-power sleep state until the microcontroller decides that a transmission of collected sensor data is required. The microcontroller can then wake up the radio, perform the required transmission, and then revert to sleep mode.

In some cases, a burst of data transmission across the wireless network might only occur when a small, intermittent energy-harvesting power supply has accumulated enough energy in a capacitor to power a transmission. Alternatively, a low-power wireless sensor node can “wake-on-radio”, only taking the microcontroller out of its sleep state when a message is received over the wireless network requesting a sensor readout and only powering up the sensors and microcontroller at this time.

With most of the components of the system, such as the microcontroller, radio and sensors – each kept off-line or asleep for the largest practical amount of time – efficiently designed wireless sensor nodes may achieve operating timescales as long as years off a single battery. Today’s typical wireless RF microcontroller system-on-chips targeted at IoT applications typically consume about 1-5 microwatts in their “sleep” state, increasing to about 0.5-1.0 mW when the microcontroller is active, and up to around 50 mW peak for brief periods of active RF transmission.

However when considering the design of energy-efficient, low-power IoT sensor networks, it can sometimes be advantageous to think not just in terms of power consumption, but in terms of the amount of energy required to perform a particular operation. For example, let’s suppose that waking up a MEMS accelerometer from sleep, performing an acceleration measurement and then going back to sleep consumes, say, 50 micro joules of energy; or that waking up an RF transceiver from sleep, transmitting a burst of 100 bytes of data and then going back to sleep consumes 500 micro joules.

If we know the specific energy consumption of each operation, then the average power consumption is simply the energy per operation multiplied by the frequency of that operation, summed over the different kinds of operations. Of course, this assumes that the continuous power consumption of each device when it is asleep is very small and can be ignored. Alternatively, if we have a certain known power budget available and a known energy budget for each sensing, computation or transmission operation – we then know the maximum practical frequency at which a sensor node can perform sensor measurements and transmit its data.

Additionally, efficient wireless sensor nodes can take advantage of some form of energy harvesting power supply – employing energy sources such as solar cells, vibrational energy harvesters or thermoelectric generators to minimise maintenance and extend battery life – with the possibility of completely eliminating external power supplies, but only if the power consumption of the system is small enough and a capacitor is employed for energy storage.

In many applications, solar cells are the most familiar and relatively mature choice for low-power network nodes operating outdoors or under good indoor light conditions. However, other technologies suitable for extracting small amounts of power from the ambient environment exist. For example, a wireless sensor node set up to monitor bearing wear in a generator could employ a piezoelectric crystal as a vibrational energy harvester, converting motor vibration into usable energy, or a thermoelectric generator mounted on a hot exhaust could harvest a small amount of otherwise wasted energy from the thermal gradient.

Typical vibrational energy harvesters usually operate with a cantilever of piezoelectric material that is clamped at one end and tuned to resonate at the frequency of the vibration source for optimal efficiency – although an electromagnetic transducer can be used in some cases. Whilst the electrical power available is dependent on the frequency and intensity of the vibrations, the cantilever tip mass and resonant frequency can generally be adjusted to match the machinery or system that energy is to be harvested from.

Furthermore, energy harvesting management ICs that manage the accumulation of energy in a capacitor over a period of time can enable short bursts of relatively high power consumption, such as when a node wakes up and transmits a burst of data, and are particularly well suited to low-power wireless sensor nodes.

Even with the examples mentioned above, the energy-efficiency possibilities are significant and can be a reality. When designing prototypes or proof-of-concept demonstrations you may put energy use to one side, however when it comes time to generate a real, final product – you can only benefit from taking energy-efficiency into account.

If you are considering creating or modifying existing designs and not sure about the energy-saving and generating options that are available, be efficient and discuss your needs with an organisation that has the knowledge, experience and resources to make your design requirements a reality such as here at the LX Group.

At the LX Group we have a wealth of experience and expertise in the embedded hardware field, and can work with the new and existing standards both in hardware and software to solve your problems. Our goal is to find and implement the best system for our customers, and this is where the LX Group can partner with you for your success.

Published by LX Pty Ltd for itself and the LX Group of companies, including LX Design House, LX Solutions and LX Consulting, LX Innovations.