LIDAR 3D Imaging on a Budget

PIC-32-Based Design

Demand is on the rise for 3D image data in a variety of applications. That has spurred research into LIDAR systems capable of keeping pace. Learn how this Cornell student leveraged inexpensive LIDAR sensors to build a 3D imaging system—all within a budget of around $200.

By Chris Graef

There’s a growing demand for 3D image data in a variety of applications, from autonomous cars to military base security. This has prompted research into high precision LIDAR systems capable of creating extremely clear 3D images to meet this demand. While these high-end systems can produce accurate and precise images, they can cost on the order of multiple thousands to tens of thousands of dollars. A side effect of this research, however, is the increasing availability of LIDAR devices at a cost much more affordable for tinkerers, students, hobbyists and budget-constrained embedded system developers. Using this new supply of inexpensive LIDAR sensors, I was able to build a 3D imaging system with a budget of around $200. The major parts used for the system can be seen in Table 1.

Table 1 Shown here are the cost and quantity of the major components used in the project. Not included are some smaller components such as wires, resistors and op amps.

At a glance, my LIDAR scanner works by turning a single-point LIDAR range finder through a scan pattern. I use a Microchip PIC32 microcontroller to control two analog feedback servos—one setting azimuth angle and one setting altitude angle—to move a mounted LIDAR distance sensor through a scan pattern. By synchronizing the feedback data of these two servos with the distance readings from the LIDAR sensor, the system defines one point in 3D space in a spherical coordinate format. After allowing the system time to create 10,000 to 20,000 points, the result is a 3D image made up of distinct spatial points. These points are stored in a point cloud data file format, which can be displayed by graphing software such as MATLAB.

MECHANICAL DESIGN

A CAD model of the imaging system is shown in Figure 1. The servos are shown in blue, the LIDAR is shown in red and the 3D printed mounts are shown in gray. All the components are connected using nuts and machine screws. The lower (azimuth) servo rotates the entire apparatus above it. The upper (altitude) servo rotates just the LIDAR sensor. The combined motion of the two servos results in the scan pattern of the system.

Figure 1
A CAD model of the LIDAR sensor and servo mounting. The LIDAR sensor is shown in red, the servos are shown in blue and the mounting brackets are shown in gray.

One thing to note in this design are the slots used on the mounting brackets to fasten both the altitude servo and the LIDAR sensor. One of the biggest requirements for the mechanical design of this project was to ensure that the center of rotation for the LIDAR sensor was in the center of the scanner. If the LIDAR sensor is positioned away from either axis of rotation, error gets introduced into the system. Here’s why this occurs: When converting raw data to cartesian points, we assume that the LIDAR sensor is giving us the distance to a point in 3D space from the origin of our spherical coordinate space. Deviation from the center of rotation for the azimuth or altitude angle would mean that we are recording a distance from somewhere else in our geometric plane.

It’s still possible to get accurate 3D points if the LIDAR sensor is not at the center of rotation, but this requires precise measurement of where the LIDAR sensor actually is in our coordinate space, and the use of complex mathematics to transform the measured data into accurate 3D position points. I thought that adding a couple of slots to a 3D bracket would be slightly easier and more effective. These slots allow for micro adjustments to be made in two dimensions, so that the LIDAR sensor lies in the direct center of both axes of rotation.

ELECTRICAL DESIGN

There are two main electrical circuits in this design: The power/servo control circuit and the feedback amplifier circuit.The power/servo control circuit shown in Figure 2 was designed to allow the PIC32 MCU to send a pulse width modulation (PWM) signal to the servos, while protecting the MCU from possibly harmful electrical noise made by the servo motors. The first step to reduce noise was to use an opto-isolator as a switch for the servo motors control pin. By driving pins RPB9 and RPB7 high, the MCU connects the servo motors’ control pin to the 5-V source. This converts the PIC32’s 3.3-V PWM output into a 5-V PWM usable by the two servos, while isolating the PIC32’s output pin from any electrical noise.

Figure 2
Shown here is the circuit of the power supply module. The servos are shown as motors. The RPB9 and the RPB7 are wires connected to output pins on the PIC32.

If the servos were the only things that needed to be connected to the MCUs, then the opto-isolator configuration would have been enough to protect the PIC32 from the servo motors’ electrical noise. However, the MCU must share a common ground with the LIDAR sensor, to be able to read the sensor’s analog output. This means electrical noise on the power/servo controller circuit can travel to the PIC32 through this common ground. To reduce the chance of electrical damage, two capacitors—one ceramic and one electrolytic—were connected across the 5-V source and the ground. The smaller ceramic capacitor attenuates any smaller amplitude, high frequency noise and the larger electrolytic capacitor is used to attenuate the lower frequency noise. The combination of these two capacitors ideally stops any damaging noise from travelling through the power connection by shunting the noise to ground instead.  …

Read the full article in the September 338 issue of Circuit Cellar

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3D Gesture Recognition Controller for Cars

Microchip Technology has announced a new 3D gesture recognition controller that offers the lowest system cost in the automotive industry, providing a durable single-chip solution for advanced automotive HMI designs. The MGC3140 joins Microchip’s family of easy-to-use 3D gesture controllers as the first qualified for automotive use.

Suited for a range for applications that limit driver distraction and add convenience to vehicles, Microchip’s new capacitive technology-based air gesture controller is ideal for navigating infotainment systems, sun shade operation, interior lighting and other applications. The technology also supports the opening of foot-activated rear liftgates and any other features a manufacturer wishes to incorporate with a simple gesture action.
The MGC3140 is Automotive Electronics Council AEC-Q100 qualified with an operating temperature range of -40°C to +125°C, and it meets the strict electromagnetic interference (EMI) and electromagnetic compatibility (EMC) requirements of automotive system designs. Each 3D gesture system consists of a sensor that can be constructed from any conductive material, as well as the Microchip gesture controller tuned for each individual application.

Car manufacturers are increasingly seeking ways to reduce driver distraction through implementing functional safety technology in vehicles. Many Human Machine Interface (HMI) designers are turning to gesture recognition as a solution to improve driver and vehicle safety without sacrificing interior design, adding features that allow drivers to easily control everything from switching on lights to answering phone calls while focusing on the road.

While existing solutions such as infrared and time-of-flight technologies can be costly and operate poorly in bright or direct sunlight, the MGC3140 offers reliable sensing in full sunlight and harsh environments. Other solutions on the market also come with physical constraints and require significant infrastructure and space to be integrated in a vehicle. The MGC3140 is compatible with ergonomic interior designs and enables HMI designers to innovate with fewer physical constraints, as the sensor can be any conductive material and hidden from view.

The Emerald evaluation kit provides a convenient evaluation platform for the 3D gesture recognition controller. The kit includes a reference PCB with the MGC3140 controller, a PCB-based sensor to recognize gestures, as well as all needed cables, software and documentation to support an easy-to-use user experience. All parts are compatible with Microchip’s Aurea software development environment which supports all Microchip 3D gesture controllers.

The MGC3140 is available now in sampling and volume production quantities.

Microchip Technology | www.microchip.com

3D Tool Strengthens Marriage of PCB Design with Mechanical Design

Cadence Design Systems has announced its Cadence Sigrity 2018 release, which includes new 3D capabilities that enable PCB design teams to accelerate design cycles while optimizing cost and performance. According to the company, a 3D design and 3D analysis environment integrating Sigrity tools with Cadence Allegro technology provides a more efficient and less error-prone solution than current alternatives using third-party modeling tools, saving days of design cycle time and reducing risk.

In addition, a new 3D Workbench methodology bridges the gap between the mechanical and electrical domains, allowing product development teams to analyze signals that cross multiple boards quickly and accurately.

Since many high-speed signals cross PCB boundaries, effective signal integrity analysis must encompass the signal source and destination die, as well as the intervening interconnect and return path including connectors, cables, sockets and other mechanical structures.

Traditional analysis techniques utilize a separate model for each piece of interconnect and cascade these models together in a circuit simulation tool, which can be an error-prone process due to the 3D nature of the transition from the PCB to the connector. In addition, since the 3D transition can make or break signal integrity, at very high speeds designers also want to optimize the transition from the connector to the PCB or the socket to the PCB.

According to the company, the Sigrity 2018 release enables designers to take a holistic view of their system, extending design and analysis beyond the package and board to also include connectors and cables. An integrated 3D design and 3D analysis environment lets PCB design teams optimize the high-speed interconnect of PCBs and IC packages in the Sigrity tool and automatically implement the optimized PCB and IC package interconnect in Allegro PCB, Allegro Package Designer or Allegro SiP Layout without the need to redraw.
Until now, this has been an error-prone, manual effort requiring careful validation. By automating this process, the Sigrity 2018 release reduces risk, saves designers hours of re-drawing and re-editing and can save days of design cycle time by eliminating editing errors not found until the prototype reaches the lab. This reduces prototype iterations and potentially saves hundreds of thousands of dollars by avoiding re-spins and schedule delays.

A new 3D Workbench utility available with the Sigrity 2018 release bridges the mechanical components and the electronic design of PCB and IC packages, allowing connectors, cables, sockets and the PCB breakout to be modeled as one with no double counting of any of the routing on the board. Interconnect models are divided at a point where the signals are more 2D in nature and predictable. By allowing 3D extraction to be performed only when needed and fast, accurate 2D hybrid-solver extraction to be performed on the remaining structures before all the interconnect models are stitched back together, full end-to-end channel analysis can be performed efficiently and accurately of signals crossing multiple boards.

In addition, the Sigrity 2018 release offers Rigid-Flex support for field solvers such as the Sigrity PowerSI technology, enabling robust analysis of high-speed signals that pass from rigid PCB materials to flexible materials. Design teams developing Rigid-Flex designs can now use the same techniques previously used only on rigid PCB designs, creating continuity in analysis practices while PCB manufacturing and material processes continue to evolve.

Cadence | www.cadence.com

New 3D NAND SSDs for Embedded Applications

Interested in wafer-packaged NAND flash storage solutions?  ATP Electronics recently launched a new generation of storage solutions using the  latest 3D NAND flash technologies. These new 3D NAND-based SSDs are targeted at the industrial and embedded markets for industrial, IoT, medical, automotive, and telecom applications.ATP NAND SSDs

ATP provides various chip densities using DDP, QDP, and even ODP die-stacking while using the same wafer stock. This offers flexibility in supply chain, and also enables ATP to ramp multiple product densities quickly. The new 3D NAND solutions are reliable, cost-effective storage solutions.

Source: ATP Electronics

3-D Integration Impact and Challenges

People want transistors—lots of them. It pretty much doesn’t matter what shape they’re in, how small they are, or how fast they operate. Simply said, the more the merrier. Diversity is also good. The more different the transistors, the more useful and interesting the product. And without any question, the cheaper the transistors, the better. So the issue is, how best to achieve as many diverse transistors at the lowest cost possible.

One approach is more chips. Placing a lot of chips close together on a small board will produce a system with many transistors. Another way is more transistors per chip. Keep on scaling the technology to provide more transistors in one or a few chips.

silicon chipThe third option combines these two approaches. Let’s have many chips with many transistors and end up with a huge number of transistors. However, there is a limit to this approach. It’s well understood that scaling is coming to an end. And placing multiple chips on a board can have a terrible effect on a system’s overall speed and power dissipation.

But there is an elegant and intellectually simple solution. Rather than connecting these chips horizontally across a board, connect them vertically, providing N times more transistors, where N is the number of chips stacked one above another. Such vertical, 3-D integration was first broached by William Shockley, co-inventor of the transistor at Bell Labs in 1947. Shockley described the 3-D integration concept in a 1958 patent, which was followed by Merlin Smith and Emanuel Stern’s 1967 patent outlining how best to produce the holes between layers. We now call these inter-layer holes through silicon vias (TSVs). Technology is still catching up to these 3-D concepts.

Three-dimensional integration offers exciting advantages. For example, the vertical distance between layers is much shorter than the horizontal dimensions across a chip. Three-dimensional circuits, therefore, operate faster and dissipate less power than their 2-D equivalent. A 3-D system is shockingly small, permitting it to fit much more conveniently into a tiny space. Think small portable electronics (e.g., credit cards).

But the most exciting advantage of 3-D integration isn’t the small form factor, higher speed, or lower power; it’s the natural ability to support many disparate technologies and functions as one integrated, heterogeneous system. Even better, each chip layer can be optimized for a particular function and technology, since the individual chips can each be developed in isolation. No more trading off different capabilities to combine disparate technologies on the same chip. Now we can use the absolute best technology for each layer and a completely different and optimized technology for a different layer. This approach enables all kinds of novel applications that until now couldn’t have been conceived or would have been cost-prohibitive.

Imagine placing a microprocessor plane below a MEMS-accelerometer plane below an analog plane (with ADCs) below a temperature sensor, all below a video imager (which has to be at the top to “see”). All of these planes fit together into a tiny (smaller than a fingernail) silicon cube while operating at higher speeds and dissipating lower power.

There are technical issues, including: how to best make the TSVs, how to construct the system architecture to fully exploit the system’s 3-D nature, how to deliver power across these multiple planes, how to synchronize this system to best move data around the cube, how to manage system design complexity, and much more.

Two issues rise to the top. The first is power dissipation (specifically, power density). When many transistors switch at a high rate within a tiny volume, the temperature rises, which can impair performance and reliability. I believe this issue, albeit difficult, is technically solvable and simply will require a lot of good engineering.

The real problem is cost. How do we mature this technology quickly enough to drive the costs down to a point where volume commercial applications are possible? Many companies are close to producing tangible 3-D-based products. Cubes of highly dense memory will likely be the first serious and cost-effective product. Early versions are already available. Three-dimensional integration will soon be here in a serious way with what will be a fascinating assortment of all kinds of exciting new products. You won’t have to wait too long.

3-D Printing with Liquid Metals

by Collin Ladd and Michael Dickey

Our research group at North Carolina State University has been studying new ways to use simple processes to print liquid metals into 3-D shapes at room temperature. 3-D printing is gaining popularity because of the ability to quickly go from concept to reality to design, replicate, or create objects. For example, it is now possible to draw an object on a computer or scan a physical object into software and have a highly detailed replica within a few hours.

3-D printing with liquid metals: a line of dollsMost 3-D printers currently pattern plastics, but printing metal objects is of particular interest because of metal’s physical strength and electrical conductivity. Because of the difficulty involved with metal printing, it is considered one of the “frontiers” of 3-D printing.
There are several approaches for 3-D printing of metals, but they all have limitations, including high temperatures (making it harder to co-print with other materials) and prohibitively expensive equipment. The most popular approach to printing metals is to use lasers or electron beams to sinter fine metal powders together at elevated temperatures, one layer at a time, to form solid metal parts.

Our approach uses a simple method to enable direct printing of liquid metals at room temperature. We print liquid metal alloys primarily composed of gallium. These alloys have metallic conductivity and a viscosity similar to water. Unlike mercury, gallium is not considered toxic nor does it evaporate. We extrude this metal from a nozzle to create droplets that can be stacked to form 3-D structures. Normally, two droplets of liquid (e.g., water) merge together into a single drop if stacked on each other. However, these metal droplets do not succumb to surface-tension effects because the metal rapidly forms a solid oxide “skin” on its surface that mechanically stabilizes the printed structures. This skin also makes it possible to extrude wires or metal fibers.

This printing process is important for two reasons. First, it enables the printing of metallic structures at room temperature using a process that is compatible with other printed materials (e.g., plastics). Second, it results in metal structures that can be used for flexible and stretchable electronics.

 

Stretchable electronics are motivated by the new applications that emerge by building electronic functionality on deformable substrates. It may enable new wearable sensors and textiles that deform naturally with the human body, or even an elastic array of embedded sensors that could serve as a substitute for skin on a prosthetic or robot-controlled fingertip. Unlike the bendable polyimide-based circuits commonly seen on a ribbon cable or inside a digital camera, stretchable electronics require more mechanical robustness, which may involve the ability to deform like a rubber band. However, a stretchable device need not be 100% elastic. Solid components embedded in a substrate (e.g., silicone) can be incorporated into a stretchable device if the connections between them can adequately deform.

Using our approach, we can direct print freestanding wire bonds or circuit traces to directly connect components—without etching or solder—at room temperature. Encasing these structures in polymer enables these interconnects to be stretched tenfold without losing electrical conductivity. Liquid metal wires also have been shown to be self-healing, even after being completely severed. Our group has demonstrated several applications of the liquid metal in soft, stretchable components including deformable antennas, soft-memory devices, ultra-stretchable wires, and soft optical components.

Although our approach is promising, there are some notable limitations. Gallium alloys are expensive and the price is expected to rise due to gallium’s expanding industrial use. Nevertheless, it is possible to print microscale structures without using much volume, which helps keep the cost down per component. Liquid metal structures must also be encased in a polymer substrate because they are not strong enough to stand by themselves for rugged applications.

Our current work is focused on optimizing this process and exploring new material possibilities for 3-D printing. We hope advancements will enable users to print new embedded electronic components that were previously challenging or impossible to construct using a 3-D printer.

Collin Ladd (claddc4@gmail.com)  is pursuing a career in medicine at the Medical University of South Carolina in Charleston, SC. Since 2009, he has been the primary researcher for the 3-D printed liquid metals project at The Dickey Group, which is headed by Michael Dickey. Collin’s interests include circuit board design and robotics. He has been an avid electronics hobbyist since high school.

Collin Ladd (claddc4@gmail.com) is pursuing a career in medicine at the Medical University of South Carolina in Charleston, SC. Since 2009, he has been the primary researcher for the 3-D printed liquid metals project at The Dickey Group, which is headed by Michael Dickey. Collin’s interests include circuit board design and robotics. He has been an avid electronics hobbyist since high school.

Michael Dickey (mddickey@ncsu.edu) is an associate professor at the North Carolina State University Department of Chemical and Biomolecular Engineering. His research includes studying soft materials, thin films and interfaces, and unconventional nanofabrication techniques. His research group’s projects include stretchable electronics, patterning gels, and self-folding sheets.

Michael Dickey (mddickey@ncsu.edu) is an associate professor at the North Carolina State University Department of Chemical and Biomolecular Engineering. His research includes studying soft materials, thin films and interfaces, and unconventional nanofabrication techniques. His research group’s projects include stretchable electronics, patterning gels, and self-folding sheets.