What are the components of a smart sensor?
July 24, 2018
The ultimate goal of a smart sensor is that it be completely autonomous. That means it sources its own energy, performs all of its functions and communicates with the outside world wirelessly.
This is part fourteen of a series. Read part thirteen here.
Earlier I showed you a block diagram of a smart sensor. It was to be used for an artificial vision system as part of a research project being done at the University of Southern California (see blog 12). I’ve included the block diagram to remind you of what it looked like.
But now I will simplify the concept to three blocks:
- Power management
- Processor system
The ultimate goal of a smart sensor is that it be completely autonomous. That means it sources its own energy, performs all of its functions and communicates with the outside world wirelessly. An interesting conclusion is that this ultimate smart sensor would have no pins on it. My mental view of how this plays out is to have three independent subsystems in the smart sensor. One of the subsystems handles all of the power management assets, one handles all of the performance aspects and one subsystem handles all of the personality aspects of the smart sensor. Each of these three independent subsystems can be connected together to create the smart sensor. With this flexibility, various methods of energy management can be developed then mixed and matched with various processor systems. Finally, different personality boards with different arrays of sensors can be attached to the other two subsystems to create different smart sensors.
With this as background, let me quickly discuss each of the three blocks.
Power management (Green)
There are three sub blocks of the power management system:
- Energy source
- Energy buffer
- Energy manager
I use the term “energy scavenging” to describe the concept. The smart sensor needs to obtain a continuous source of energy from the surrounding environment. Sources of energy can be light, heat, vibration, or chemical to name a few. Many years ago I visited a start-up company at Technion University in Haifa, Israel. They were working on a concept of putting piezo plates underneath the surface of roadways. Using the embedded plates, energy would be created when cars and trucks drove over them. They would be scavenging road energy. I found them asking an interesting question: What would we do with the energy? My answer was simple: Light up the next kilometer of street lights. From that discussion, I began to look further for energy sources on our highways. It dawned on me that barriers were being built on each side of major highways to keep the sound energy away from neighborhoods. Aha! Another source of energy.
I use the term energy buffer, as most electrical engineers jump quickly to the answer of a battery or capacitor. I want us to think beyond the obvious and include things like springs, balloons, gravity, etc. Of course the purpose of the energy buffer is to collect energy from the energy source in the form it is captured, and then make it available to the rest of the smart sensor in an appropriate form. For example, the energy from the energy source might be in micro-volts and micro-amps while the rest of the system may need volts and milliamps.
An important aspect of the smart sensor is the management of the energy and how it will be applied to the rest of the system. In a later blog, I’ll talk about some work that was done at MIT on energy management.
Processor system (Blue)
The processor system consists of the microcontroller and the communications link. Other components can be added in order for the system to be optimal. System-in-Package is one way to neatly put those components into one place.
The personality block is where the smart sensor fit in to the system. Where the other two blocks are the support structure for the smart sensor, this block is where various sensors, actuators, and other elements are included which give the smart sensor its value.
So, that is a quick view of what a smart sensor is and now for a couple of questions:
- I have used the term “energy buffer” rather than battery. What are some interesting energy buffers?
- In a smart image sensor, how many pixels and how many bits per pixel are needed?
- Does a smart sensor really need a processing element? If so, at what performance?
- Name some interesting ways to scavenge energy?
- How many pins does a smart sensor need?