Sensor nodes in the IoT

What’s the secret to getting off the grid and operating autonomously? Getting your system down to operate at a low-enough power such that it can run off of harvested energy and/or off of a battery that won’t need changing until after the sensor itself becomes obsolete. Only then do you have a truly autonomous, hands-off system. This system continues giving you the data and measurements you need for as long as you need them, with hardly any intervention from you.

An important key to these autonomous systems is the sensor’s usefulness in reporting collected data. If a sensor can collect a bunch of data but is unable to transmit this data – or a decision based on the data – it’s worthless. And since this sensor is unplugged or remote, it must transmit its data wirelessly. Enter the Internet of Things (IoT) to save the day.

Today, with fully powered and autonomous sensors and an IoT network around it, you can install sensors anywhere to monitor anything: vibrations in different portions of your car, the integrity of a bridge, or even the orientation of a satellite in outer space.

For an example of such a sensor, see the solar-powered dice in Figure 1. Using six solar panels, the dice operates entirely off of harvested light. The basic lighting in almost any room is sufficient to power the devices included in a sensor node like this.  These include an ultra-low-power: accelerometer, CC430 transceiver and of course a power supply.

The solar dice is an ultra-low-power optimized sensor node in the IoT.

Figure 1. The solar dice is an ultra-low-power optimized sensor node in the IoT.

When the dice is rolled, the system wakes up and transmits data to a universal serial bus (USB) dongle on a PC. What data, you might ask? The orientation of the dice, of course. Knowing this allows you to know which number was rolled based on which side is up. The only downside is that it reports this data after the dice is rolled and not before. Otherwise, this type of sensor node would come in very handy for placing bets, if used in casinos all over the world.

How does this dice relate to your sensor nodes you might ask?  The solar dice is just an example of what you can do with ultra-low power optimized devices to sense something and report this something back to you. But, for example, if you are designing a satellite, it’s directly applicable as you need to know which way you’re pointed (orientation) and don’t have the luxury of being plugged into the grid (you need energy harvesting). 

If you think about measuring vibrations in a car, an ultra-low power concept of the solar dice could allow smaller gauge wires to be used (which are cheaper and lighter) to power each sensor.  As well, fewer wires may be required since the data is transmitted wirelessly.  Swap out the accelerometer with a vibration sensor, and your sensor node is complete.

What types of sensors would you like to unplug using the solar-dice concept?

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