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Raspberry Pi 4 Armchair Datasheet Evaluation

Are the performance improvements possible?

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With the introduction of the Raspberry Pi 4, I dug into the announcement and datasheet while waiting for mine to arrive. Well, “datasheet” might be an exaggeration, but there is a list of the Raspberry Pi 4 tech specs available. That link gives a bullet item list of the main specs. In this post, I focus on these four:

  • Broadcom BCM2711, Quad core Cortex-A72 (ARM v8) 64-bit SoC @ 1.5GHz
  • Up to 4GB LPDDR4-2400 SDRAM (depending on model)
  • Gigabit Ethernet
  • 2 USB 3.0 ports; 2 USB 2.0 ports.

There is a lot of very cool stuff on this $35 board. (Amazing they have kept that price point!) Or even the 4 GB $55 board. Adding Bluetooth 5, H.265 AND H.264 decoding, USB-C connector (Power), and changing the SoC to a 28 nm process are all significant improvements.

But, being an engineer and a person on the Internet, I am required to nitpick, and armchair engineer this (now) released product (that I haven’t touched yet.) Without doubt there will be a number of benchmarks posted along with the release of the Pi 4. And I expect many of those only benchmark individual components. For example, I already saw graphs on the Gigabit Ethernet speed and USB 3.0 throughput, but not at the same time. As you will see in my datasheet evaluation, using two USB devices at the same time has a performance penalty.

First, what is new with the SoC?

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Introducing Bit Preserve

Recreating vintage schematics with KiCad

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Bit Preserve Banner

A project I work on in my spare time is creating a portable Apple II. Like many of my projects, one leads into another. I started out wanting to make a mobile Apple II, and now I’m working on a project called Bit Preserve. How did I get from one project to the next? Well, as I looked into how to make a portable Apple II, I realized a significant issue. The original Apple II logic board has almost 80 ICs. Being a design from 1975, they are all through-hole packages. The good news is that except for the ROM chips, they are all off-the-shelf components. But such a size means it might be impossible to turn it into something handheld. I almost abandoned the project. Then, I learned about a chip included in the Apple IIgs. The name of the ASIC is “MEGA II.” (Nothing to do with Arduino.) It is a chip that integrates all of those off-the-shelf chips into an 84 pin package.

As I dove deeper into the project, I realized I needed other support chips to make the MEGA II useful. There is a decent book that discusses the technical details of the Apple IIgs, but it does not get into chip or board level design. For that detail, I had to look at the original schematics. While I am ecstatic that someone archived these original documents as PDFs, I quickly became frustrated. Sometimes the scan quality is not very good, and it is nearly impossible to search for symbols across multiple pages. I thought to myself, “There has got to be a better way!”

Bit Preserve on GitHub

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Bald Engineer’s ESD Must-Haves | Workbench Wednesdays

element14 Presents on YouTube
2019-06-04

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 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 electrostatic discharge; 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
  • Electrostatic Discharge Mat Cleaner

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

More info on element14

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New Arduino Nano board from Maker Faire 2019

Is the new Arduino Nano Every, IoT, BLE, and BLE Sense worth it?

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New Arduino Nano Every at Maker Faire 2019

I had the chance to spend some time with the Arduino team before and during Maker Faire Bay Area 2019. I also attended Massimo’s “State of Arduino” talk. In short, there are new Arduino Nano boards coming, a certification available today, updates on the Vidor, interesting education kits, and one more special announcement.

It rained most of the weekend, which I am sure caused attendance to take a hit. Normally this would not be a big deal, but there was some talk it may be the last year for the Bay Area’s show. As usual, I walked the show on Friday and did take note there were several new exhibitors throughout. For that reason, I hope it is not the last one.

Depsite the grim news, spirits from attendees were high. On Saturday I helped answer questions and give out t-shirts at the Arduino booth. The time flew by fast but not before I got to overhear and explain tidbits about this year’s Arduino announcements.

New Arduino Nano (Every, IoT, BLE, and BLE Sense)

My favorite announcement, hands down, is the new Arduino Nano boards. The boards are a new small form factor featuring castellated edges. A “castellated edge” means you can solder the entire module to a PCB. It is a cost-effective way for adding a complex microcontroller solution to small and medium run products. You might be familiar with the concept from the ESP, WiFi, or Bluetooth modules.

The board form factor is really the only thing these new Arduino Nano boards have in common. Each offers a slightly different feature set. Oh, and the price for each is shocking for an Arduino branded board.

New Arduino Nano Every

New Arduino Nano Every

Arduino Nano Every

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6 things I learned about KiCad at KiCon 2019

Re-cap of the stuff I found interesting at the first conference for hardware developers

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KiCon 2019 Review

In April 2019, hardware hackers, hobbyist, and engineers joined together for the first KiCon. A couple of people asked me, “why is there a conference for KiCad?” Some questioned if KiCad was significant enough software to warrant a conference. That question is valid. But KiCon is larger than the KiCad software. Even in its first iteration, KiCon evolved more into a meeting for people building electronics hardware from small scale hobbyist to professionally designed systems, than just a conference on a single piece of software. Some might call it a maker conference. I call it a hardware developer conference. The key that tied everyone together is the open source software behind our printed circuit boards.

Twenty-five different talks covered basic KiCad usage, automating tasks, PCB layout techniques, and projects designed in KiCad. Wayne Stambaugh ended the first day with a State-of-KiCad discussion. He introduced the feature list for KiCad 6. Additionally, he announced four new lead developers and that he would be working on KiCad full time. That news means it is likely KiCad 6 will be here faster than the usual two-year release cycle.

In addition to the talks, there were several workshops and panel discussions. The workshops included a getting started with KiCad lead by Shawn Hymel [link]. That one was cool to keep an eye on because people were designing their first PCB, milling it, and then soldering parts to make the boards blink. In another workshop, Anool Mahidharia provided a hands-on guided introduction to FreeCAD. It is a parametric mechnical cad tool. The panels featuerd PCB manufactureres, workflow discussions, and the KiCad development team.

Outside of the planned classes and activities, I finally shook hands with friends whom I only knew through social media. Even though we are all electronics enthusiast or professional engineers, it is rare we end up at the same place at the same time. See what I mean about KiCad connecting liked minded people together?

With so much going on, I realized I couldn’t cover everything. Instead, this post’s focus is the tidbits I learned at the conference and stuck with me after a little bit of time passed. Here are the six things I learned at KiCon 2019.

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Tenma 72-2660 Portable Hand Held Supply | Workbench Wednesdays

element14 Presents on YouTube
2019-05-08

The TENMA 72-2660 portable power supply offers bench supply capability in a backpack friendly package. The single output is capable of 45 watts with up to 30 volts and 3.75 amps out. The built-in USB ports offer an easy way to power 5 Volts Arduino or Raspberry Pi projects while limiting their current. See how this portable supply performs, the things the Bald Engineer likes about it, and the points to consider before buying

This $100 power supply, model number 72-2660, is cool. It’s about the size of a digital multimeter but can output 45 Watts. Both voltage and current are adjustable. It can output up to 30 volts and 3.75 amps, but not at the same time. It does have a flaw in its design though. Fortunately, I was able to find and apply a fix for it. Overall, if you want a portable adjustable supply, this one is worth checking out.

If you are new to bench or lab power supplies, check out this bench power supply basics video.

To answer a common question: yes, I did injury my shoulder. Right before shooting the A-Roll, the parts with me on camera, I tripped. As I went to catch myself falling, I tore two of the muscles in my shoulder. It took about 6 weeks to completely heal. Yuck!

Show notes on element14

Health and Solder Fumes | Workbench Wednesdays

element14 Presents on YouTube
2019-04-10

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.

Ask Questions on element14

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7 MOSFET Myths and Misconceptions Addressed

Let's set some things straight

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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.

Download Slides (8mb)

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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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Low switch vs High switch Banner

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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