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Techno Talk Testing Times When I was young, bright-eyed, and bushy-tailed, any test equipment worth having was too expensive for me to have. Today, by comparison, I’m amazed by the power, sophistication and affordability of the offerings available to hobbyists. T he topic of testing and the equipment we use to do so has been much on my mind of late. There are a couple of pieces of test gear I personally could not do without. The first is my trusty multimeter. Actually, “multimeters” would be more apt, because I have them all over the place. There’s one next to me on the desk here in my office, another on my desk in my study at home, one in my backpack for when I’m on the road and others lurking hither and thither. The amazing thing is how cheap they are these days (I’m talking about multimeters for hobbyists rather than professional­grade devices). You can pick up a very serviceable unit for less than £10. Scope it out Another piece of test equipment that provides myriad test functions is an oscilloscope. Back in the 1950s and 1960s, these devices were monstrous in terms of size, weight and cost. In addition to a cathode ray tube (CRT) for display, their rugged metal cabinets contained a cornucopia of valve-based electronics. Those valves (also known as vacuum tubes) used to perform tasks like controlling the vertical and horizontal deflection of the electron beam(s), amplifying signals and implementing switching and timing circuits. Oscilloscopes like that were still found in the engineering department when I started university in 1975. They were so heavy that you could give yourself a hernia lifting one, so we wheeled them around on trolleys. Things didn’t get much better in the 1980s, even though the valves were swapped out for transistors and silicon chips. Although these components were smaller and lighter, the designers of the scopes employed lots more of them to squeeze in more features and functions. It was like a ‘functionality arms race’ between the various vendors. Also, the CRT remained in the heart of the beast. A good professional-grade fourchannel oscilloscope could easily cost £10,000 back in the day, so this wasn’t something you would expect to find on a hobbyist’s desk. How things have changed. I have a four-channel Rigol 38 DS1054 rated at 50Mz and 1GSa/s with a large 7-inch LCD screen sitting next to me on my office desk. It’s small at 13 × 7 × 5 inches (33 × 18 × 13 cm), light (6.6 pounds or 3kg), and affordably priced (currently £300 on amazon.co.uk). It also lets me take screenshots directly to a USB memory stick plugged into a port on the front; a feature worth its weight in gold. Take a guess I was once offered a position based on my stating that my modus operandi for debugging things was to start with a WAG (“wild-ass guess”). “Perhaps you would care to elaborate a little”, said my interviewer. That was his big mistake. Much like my dear old mother, the real trick is getting us to stop talking. I explained that I would start with the obvious options. If the system in question was totally dead, for example, I would first check to see that it was plugged in (powered up). However, if the system was up and running but functioning erratically or incorrectly, this was where I would take a WAG based on how the system was behaving coupled with my past experiences. Even if I hadn’t seen anything like the current behaviour before, there may be clues tickling my unconscious mind. My justification was that, if it proved to be correct, depending on the size, complexity, and cost of the system, taking a WAG could save a lot of time, resources, frustration, and money. Contrariwise, if my WAG proved to be incorrect, little effort would have been expended and little time would have been lost. I could then proceed to perform a regular indepth analysis and diagnosis. I got the job (perhaps in a desperate attempt to make me stop talking)! Experience doesn’t hurt If you look at my Weird and Wonderful Arduino Projects column, which starts on page 7, you’ll see that a member of the PE community called Ian emailed me with an interesting problem. In his email, Ian said, “See the attached photo. I have checked this a million times and am convinced there are no errors”. Max the Magnificent I must admit that my first thought on reading this was, “Oh Ian, why dost thou tempt the fates so?” I quickly set up a Zoom call with my friend Joe Farr because this sort of thing goes much quicker when there are two of you doing it. Between us, Joe and I have a lot of experience in debugging things. This is largely due to the mistakes we made when putting them together in the first place. This explains why the first thing we did was to check the power and ground connections to the integrated circuits (ICs) mounted on the breadboards in Ian’s photo. At least, we checked the ground connections. We would have checked the power connections… but there weren’t any. I emailed Ian. He added the requisite wires and the circuit functioned as expected. Problem solved. Why did Joe and I check the power and ground connections before all else? We will never tell! Trust? I think not! I’m working on a new project that uses a 9V DC external power source, which I need to drop to 5V inside the device. I can get by with 5V at 1A, but I’d prefer to have 3A or more to play with. I could use a regular, cheap-andcheerful linear regulator, but they tend to run hot as the power rises. I found some small and tasty buck (step-down) regulator modules on Amazon here in the USA. With their 9-36V input and 5V <at> 5A output, these sounded too good to be true. They were indeed (too good to be true). Joe purchased some equivalents on Amazon in the UK (https://pemag.au/ link/ac2m). His arrived before mine. Joe tested them using a bench power supply and an electronic load. Oh dear. The output voltage started to droop at 1A, it fell to 4.4V by 2A, and it collapsed to 0V shortly thereafter. Thank goodness for test equipment, is all I can say! Editor’s note: even some switch-mode IC manufacturers rate their parts based on the peak current they can deliver, which can be considerably higher than PE the average! Practical Electronics | January | 2025