All About Seeing Your Projects: Optical and Digital MagnificationFebruary 14, 2021 by Mark Hughes
Smaller electronics call for more powerful inspection equipment. If you're building a collection of at-home lab equipment, these visual tools may help you see where you're going on minuscule boards.
In a previous article, we discussed the many options for test and measurement equipment—oscilloscopes, vector network analyzers, multimeters, and the like—as you set up your at-home laboratory. One thing we have yet to touch on is the equipment you'll need to properly see your projects from home.
Electronics have shrunk in size and they’re only getting smaller. 0402s are specs of sand, and now boards are regularly populated with 01005s. Passive components of this size—and their land pads—are beyond the limits of human visual acuity. You have two options to see what you are doing: optical or digital magnification.
The simplest way to see what you are doing is with a simple optical microscope. Whether you get a monocular, binocular, or trinocular microscope (or even a small loupe) is entirely up to you. One eyepiece is usually enough. But you need to make sure you have the capability to zoom out and zoom in as well as add an external illumination ring if you plan on using high magnification levels.
One of the companies I work with, Royal Circuits, uses eyepiece-less microscopes at their production facilities in Hollister and Santa Fe Springs, California.
Example of a non-contact measuring microscope. Image used courtesy of Distek Measuring Instruments
Eyepiece-less microscopes provide relief for users who have to use the devices for an entire shift. They are much easier to use and more comfortable than standard microscopes. Unfortunately, they are large and somewhat unaffordable for the typical engineer.
Amscope makes a variety of microscopes that you can consider for your home lab. They are built well, and surprisingly affordable. Image used courtesy of Amscope
Microscopes often require external illumination. The best option is a fiber optic ring light. But fiber optic ring lights cost hundreds of dollars (unless you are able to find a used one at an online auction website).
Below is a trinocular microscope solution from AmScope complete with a fiberoptic ring light to provide illumination of a printed circuit board.
The simul-focal stereo zoom microscope (3.5X-45X) includes a fiberoptic ring light and a 1.3MP camera. Image used courtesy of AmScope
The much cheaper and usually entirely adequate solution is to purchase an LED ring light.
Microscope ring light with reinforced with 56 LED and a dimmer. Image used courtesy of AmScope
This LED ring light will attach to the bottom of microscopes and most camera lenses to provide additional illumination for magnified objects.
Digital cameras provide an additional means of viewing and capturing images of your circuit board. The image sensor can come from a DSLR or from a standalone USB Microscope head. If you are going to “live-view” your project, there is no need to exceed 4K resolution (8 MP) unless you happen to have an 8K monitor or capture card. If you’re unsure if you have one, I can pretty much guarantee that you don’t. Most 16 MP cameras are only capable of still images at their specified resolution; their output is usually just HD.
This 14 MP still camera outputs HD resolution video (1920 x 1080) over USB and HDMI. Image used courtesy of Hayear Electronics
But the image sensor is only one part of the equation. You need to choose optics as well.
There are three options of lenses for whichever camera head you choose. The first and simplest is a 1–¼” diameter ring that slips into a microscope eyepiece. Light that would be projected into your eye is diverted to the camera’s imaging sensor instead.
Microscope adaptor for CCD cameras and digital eyepieces. Image used courtesy of Amazon
The second option is a stand-alone magnification lens. These lenses mount directly to the camera stand and allow you some degree of control over focus and magnification.
14MP industrial microscope camera. Image used courtesy of Hayear Electronics
The last option is my new favorite: a telecentric lens. Telecentric lenses pass rays parallel to the optical axis through the imaging optics. This is significantly different from both microscopes (which expands rays) and telescopes (which accumulate light and typically shrink objects). Telecentric lenses collimate light rays. That means that regardless of the distance between the object and the lens, objects will appear to have a constant size.
Regular lenses provide some amount of distortion to images. Objects of different distances from the lens appear to have different sizes. Telecentric lenses will show the true size of objects regardless of their distance from the lens.
Entocentric optics vs. telecentric lenses. Image (modified) used courtesy of Photonics
Unfortunately, there is no opportunity for zooming these lenses, and the field of view will always be restricted to the maximum diameter of the lens opening. But they provide distortion-free imagery of a PCB. As an example, in a normal PCB under microscopic inspection, the via cavities would appear vertical in the center of the lens and angle substantially as the viewer looks to the side. With a telecentric lens, all via cavities would appear perfectly vertical.
I have tool chests in my garage, but I want specific, frequently-used tools readily available and within arms reach: "Vampliers," flush-cutters, nut drivers, hex head drivers, etc. This again comes down to personal preference, but my latest, greatest storage solution is as simple as drilling several dozen blind holes in a piece of wood, plastic, or aluminum and storing everything vertically.
A 98-hole wooden leathercraft tool holder. Image used courtesy of Amazon
This wooden storage solution for leathercrafting tools inspired my design (which has larger diameter holes than the product shown here).
If you are designing precision analog or digital circuits, you likely need a high-quality power supply—perhaps something with multiple outputs and the ability to produce a negative potential difference. When I first went through school, the available solutions were the size and the weight of your typical boat-anchor. I still have one in the garage, where it has sat unused for at least a decade.
Direct replacements for my old power supply are available for well under $100.
DC power variable supply. Image used courtesy of Amazon
Decent-enough performance can also be found in DC-DC buck converter modules the size of a dinner roll. Several of these modules, combined in a case with a suitable AC-DC converter (of higher DC voltage), can be assembled to create a multi-output power supply in an hour or two.
Digital-programmable power supply with a regulated buck power converter. Image used courtesy of Amazon
Pocket-sized solutions exist for power supplies, too.
Mini digital power supply set. Image used courtesy of SainSmart
What underpowered tool collection wouldn’t be complete without a PocketPC! Minicomputers exist, complete with HDMI, RS232, USB, and RJ45 ports all in a form factor that’s the size of a paperback novel. With this computer, you can do almost anything! You can almost type, almost video conference, almost surf the web, almost read your emails. (In all fairness, I do know people who own and like these devices.)
Micro PC-mini laptop. Image used courtesy of Amazon
For the first time in human history, the electrical engineer has the tools available to carry an almost-adequate testing laboratory in his or her pocket. Pocket PCs, pocket multimeters, pocket oscilloscopes, and pocket power supplies exist.
What other devices do you know about? Or do you have experience with any of these pint-sized dohickeys? Let us know below.