In projects involving IoT, we must consider what will be monitored or controlled, what data will be modeled and what will be the communication protocols used. An IoT device is an electronic device or system responsible for reading sensors and controlling a process — in a factory, for example —, under the supervision of another system with which it maintains direct communication.
A little discussed point, but which is a determining factor in a project, is how to power IoT devices — power, here, means providing the energy necessary for the device’ electronic circuit to work. The aspects to consider in this project depend on where the IoT device will be used.
In agribusiness, for example, IoT devices are in the open field, which favors the use of solar energy in their power, with storage in rechargeable batteries. It is the natural path and used by most monitoring systems on farms. In the transport sector, on the other hand, IoT devices tend to integrate with vehicles and use the electrical system of the car itself for power. Since voltages are low, their power supply circuits tend to be simpler.
In manufacture, a power system can cause unexpected problems if a study is not done before decisions are made. Below, we present the two classic systems used in manufacture and a third way, still under development — and which, in the future, will be increasingly used in simpler IoT systems, such as readings from a single sensor.
Using the power grid
Any factory today has a large electric power distribution system, to which they all types of devices are connected — from a coffee maker in the offices to the many machines with electric potent motors. When implementing a system for control and monitoring via IoT, it is natural to think about using this network for the power of IoT devices — after all, it is already available throughout the factory.
In this case, when designing an IoT device, we can count that it will be connected directly into a common outlet of 127 VAC or 220 VAC or, when possible, to control panels, which usually have 24 VDC outlets.
One of the advantages of this approach is that we do not have to worry too much about energy consumption, since the consumption of an IoT device is low, when compared to the machines it will monitor. For fixed production lines, with several machines that do not change over time, using the power grid becomes a rather effective option.
The design of the power supplies of IoT appliances is simpler in this case, since the voltages are fixed and energy efficiency is not the requirement with the highest priority. The wiring for the power supply is available. The devices can simply be connected to the sockets or 24V control lines.
To monitor items that do not stay in fixed places, such as transport robots, pallets or boxes of material for production, the use of the electrical network is not possible, since we can not use the factory’s wiring. In these cases, the power source has to be in or near the IoT device.
Batteries accumulate energy that generate electric current — usually through chemical reactions. There are several types of batteries and finding the option that will meet the needs of an IoT device depends on the correct study of the use case.
In the case of mobile robots, it is simpler to use batteries to power IoT devices, since robots already have internal batteries for traction motors. In this case, the design of power supply of the circuits for IoT must take into account the power consumption of the devices, so as not to cause great impact on the autonomy of the robot.
For inventory monitoring, small devices should be used, which do not take up much space in boxes or transport pallets. That means that the circuits and batteries need to be as small as possible. As small batteries have little capacity, the consumption of the IoT circuit should be restricted to only what is needed. The data traffic with the sensors’ data and usage is small, so that the exchange of messages is done quickly.
After exchanging messages, the system enters a state of hibernation to reduce power consumption and extend battery life. From time to time, the system “wakes up”, monitors and control its sensors and takes care of the exchange of messages, returning to hibernation afterwards. Thus, ordinary, non-rechargeable batteries can be used for long periods, reducing the constant need for maintenance personnel to change batteries.
An ideal supply system would be a system that does not need a cable for connection to the external electrical network and does not depend on a battery that needs to be exchanged or recharged. Although it seems like fiction, this type of solution is already possible on a small scale, thanks to new electronic technologies with very low consumption circuits — consumption so low that energy can be collected from the air.
We know that energy cannot be created or destroyed, only transformed. In a factory, energy is constantly transformed into motion, heat or even lighting. In addition, industrial environments are surrounded by radio signals — from Wi-Fi routers, radio stations etc. It is possible to collect some — very little, in fact — of the energy that has been dispersed in the air through specific circuits. The energy can then be accumulated to power small IoT circuits.
The ways, devices and technologies used for energy collection depend on the environment where the device is installed. In places with temperature variations, for example, thermoelectric cells can be used to convert the temperature difference into electrical energy. In engine monitoring, on the other hand, one can take advantage of the vibration of the motors to convert the movement into electricity, with coils and magnets mechanically coupled to engines and machines.
Radio waves can also be harnessed by picking up the energy by an antenna and accumulating it in a capacitor until there is enough to be used for a short time by the IoT device electric circuit.
Again, it is important to be careful and use as little power as possible on IoT devices, controlling the size of messages and simplifying sensor reading so that everything is done quickly. The challenge of energy collection is greater than that of using batteries, since there is less energy being supplied and it has to be used carefully, but it is still possible. It is necessary to avoid complex functions and focus on something simpler, such as a temperature sensor, for example, that only reads and passes the data to a gateway via radio.
Without a battery or cable, the IoT electric circuit becomes more independent and can be installed more easily. Since it is small and simpler, the cost is lower and it is possible to install many more devices spread throughout the space — generating more data for analysis. It also requires less maintenance, since it does not have batteries to recharge and the circuit does not suffer from the peak power problems present in the electrical network.
When designing devices for use in IoT, we must always remember to plan the power system for the circuits. This is as important as defining which system (Wi-Fi, Bluetooth etc.) or protocol to use.
The use of the power grid is advantageous in fixed production lines, where sockets and DC power lines are available by simply connecting a cable. For monitoring things that can move in the factory, it is necessary to use batteries and plan circuits and software algorithms for consumption reduction.
New electronic circuit technologies have emerged, bringing components that consume so little energy that they can be powered by data collection devices — by vibration or even by radio waves. With low cost, these devices can be applied on a large scale, monitoring much more things on time, generating much more data for analysis.
Currently, in manufacturing, it is still difficult to escape from the two traditional types of electronic circuit power — battery and mains —, because they are the only options with practical feasibility. However, energy collection, over time, can become a good future alternative, which will give more independence and economy to data collection in industry processes.