Spectrum Analyzer Basics – Workbench Wednesdays

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A spectrum analyzer displays signals in the frequency domain. To use one, you only need to know about four controls: reference level, center frequency, and resolution bandwidth. In this episode, see how to use a spectrum analyzer and determine the transmitting frequency of a device.

The example device is my microphone transmitter. It operates around 500 MHz with FM modulation. You’ll see how I step through the spectrum analyzer controls to find the exact frequency. At the end of the episode, I show some advanced measurements you can do with a modern spectrum analyzer. My favorite one is the demodulation. (more…)

Electronic Load Basics on Workbench Wednesdays

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During the Bench Power Supply basics video, I made use of my electronic load. An electronic load can sink current from power sources such as power supplies or batteries. Loads are useful to test a power supply’s design margin or verify a battery’s capacity. See how three different instrument options from ultra low-end to midrange to high-end compare. After this element14 Presents Workbench Wednesday video, you will understand how to use modes on an electronic load like constant current and constant resistance to make different measurements.

In the video, I compare three different types of tools: a $50 battery tester from eBay, BK Precision 8540 Electronic Load, and a high-end Rohde & Schwarz NGM202. They are all capable of acting as a constant current sink. In other words, you program the current and let the supply under test run. In the case of batteries, this mode is useful to test battery life. The 8540 and NGM202 both feature other capabilities like constant resistance which, as you can imagine, acts as an electronic resistor. The cool thing about using an electronic load as a power resistor is that some of them are capable of sinking up to 10s of amps.

After submitting the video to the producers, I realized I focused very heavily on batteries. More often, you use an electronic load to test power supply boards or modules. I wish I had shown those more, but it didn’t seem like it was missing until the end. So maybe in the future I can convert tools for measuring DC/DC power supplies? However, I did cover one topic significant to me. I show just how bad 9V batteries are, a topic which I like to come back to often. So I made sure to show off just how bad they work when driven past 100 mA. (It is terrible!)

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Bench Power Supply Basics | Workbench Wednesdays

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A bench power supply makes powering circuits easy and safe. Learn how to adjust basic controls like voltage. Finally, see how “current limiting” works (and why you should use it.) See how you can use built-in series or parallel tracking to increase a bench power supply’s voltage or current output. Last, if you are in the market for a power supply, do not forget to add some leads like mini-grabbers, alligator clips, and banana plugs.

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Semiconductor Measurements | Workbench Wednesdays Review

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When it comes to transistors, there are only so many things a multimeter can measure. The DCA Pro from PEAK Electronics makes short work of testing parts like a transistor. This small device can determine pinout, component type, and essential parameters in a matter of seconds. Not only that, but it can be connected to a (Windows) PC and draw parameter curves. Check out the video review to see how the device and software works. Then head over to the element14 page where you can download a zip file full of example parts I measured for you. The free to download software can open them.

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7+ Python Engineering Modules for Electronics Engineers

Python is everywhere. Its capabilities continue to grow. Not only can you create simple scripts, but you can create full-blown applications with it. The core has been scaled down to run on 32-bit microcontrollers like the ESP32 and Adafruit Feather M0. You can even use Python engineer modules to design stuff like circuits. There are electronics Python modules that create schematics, simulate circuits, and make solving math a cinch. Here are some of the modules I found that make Python usable for (electronics) engineering.

Up front, make sure you have a functioning Python environment. Update the package manager “pip” since all of these electronics python modules rely on it. Speaking of dependences, you may need to also install third-party libraries for some of them. From what I can tell, these all should be platform independent. However, I only tested these electronic modules with 64-bit Windows.

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Bald Engineer’s ESD Must-Haves | Workbench Wednesdays

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Electrostatic Discharge (ESD) damage can occur without you knowing it. That’s bad. However, the good news is that with little effort you can prevent it. Duratool has a kit of the most common ESD tools for any electronics workbench. It includes a large mat, grounding cable, wrist strap, ESD-safe cleaner, and a simple electronic tester. Don’t get shocked by ESD; add these simple tools to prevent it.

This review is on a kit that includes:

  • Large ESD Mat
  • Ground Cable
  • Wrist Strap
  • Wrist Strap Tester
  • ESD Mat Cleaner

Even if you aren’t interested in ESD, you might want to watch the first 30 seconds. 🙂

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Health and Solder Fumes – Workbench Wednesdays

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An overlooked danger of electronics soldering is the fumes. While the smell and smoke may not be pleasant, the chemicals in the fumes can be harmful. Is solder made with lead(Pb) your only concern? Learn about where lead-free solder came from, what different flux types mean, and two ways to keep your air (and your lungs clean.)

In the video, I show a cheap “smoke eater” and a professional fume extractor. There is a cost difference of $50 and $700 between the two. However, either is better than having nothing.

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7 MOSFET Myths and Misconceptions Addressed

Let's set some things straight

MOSFET Myths and Facts

The most popular AddOhms video is my short tutorial on MOSFET basics. In the years since I posted the video, people have sent me many questions. While answering those questions I’ve learned quite a bit as well. For example, in that video, I say that Vgs is the threshold to turn on the MOSFET. Well, it turns out, that is not entirely true. It is the threshold to turn it off! Oops. A minor point with a subtle difference, but a common MOSFET misconception.

In this post, I dispel that and other common myths and misconceptions around using MOSFETs. As with all engineering tips and tricks, this post is not a definitive guide to FETs. Instead, it is meant to be a guide to help you ask the right questions to design in the correct part.

1. Misconception: You don’t need resistors on the gate

Back when I made the AddOhms episode, I added a resistor to the MOSFET’s gate pin. Of course any time a resistor is shown in a schematic, people get worried about what complicated formula is needed to determine its value. For slow switching applications, like below 10 kHz, the resistor value doesn’t matter. Something in the 100 to 1000 KOhm range is fine.

P-Channel with series gate resistor

P-Channel with series gate resistor

So if the value does not matter, why have one? The gate of a MOSFET is a small capacitor. And what happens when applying a voltage to a capacitor? It starts charging.

Resistor-Capacitor Charging Curve: Voltage and Current

Resistor-Capacitor Charging Curve: Voltage and Current

The initial current is very high. It slows down as the capacitor charges. That initial current rush, also known as in-rush current, can be a problem. Even though it is a short time, there is a significant current surge that can damage an I/O pin. Depending on the size of the MOSFET’s gate capacitance, it may not be necessary to include that resistor. I wish I could say to “just” add it any time you use a MOSFET. If there is a high switching frequency, say 100 kHz or higher, then you have to worry about the RC charging curve created by the resistor and the gate capacitance.

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Classic, vintage, or retro computer systems are well documented on sites like Wikipedia. Their historic position is well known. Their schematics are even published from original documentation. But how useful are those schematics in their current form? (Spoiler, not much.) Presented at KiCon 2019.

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Low side vs. High side transistor switch

Why do these both exist, how do they work, and when do you use them?

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A common task for a transistor is switching a device on and off. There are two configurations for a transistor switch: low side and high side. The location of the transistor determines the type of circuit and its name. Either transistor configuration can use a BJT or MOSFET.

In this post, I draw the configuration for both transistor types, talk about which requires a driver, and explain why you would use either. If you are new to transistors, check out the resource links at the bottom. I have a couple of videos I made and some from element14’s The Learning Circuit which do a great job introducing transistors.

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