Day: August 19, 2024

This Is Not A Laptop, It’s A KVM Combo

August 19, 2024 by 62 Comments

A spare monitor and keyboard are handy things to have around, but they’re a bit of a hassle. They are useful for hardware development, plugging in to headless servers, or firing up a Raspberry Pi or similar single-board computer (SBC). If that’s something you do and portability and storage space are important to you, then you may be interested in the CrowView Note.

I got an opportunity to test and provide feedback on an early version of this unusual device, which is functionally a portable spare monitor plus keyboard (and touchpad) without the bulk and extra cables. Heck, it’s even giving me ideas as the guts of a Cyberdeck build. Let’s take a look.

What It Is

It really looks like a laptop, but it’s actually a 14″ 1920 x 1280 monitor and USB keyboard in a laptop form factor.

There is also an integrated trackpad, speakers and mic, and a rechargeable battery. That makes it capable of providing its own power, and it can even function as a power bank in a pinch. There’s an HDMI input on one side, and on the other is a full-featured USB-C port that accepts video input via the DisplayPort altmode.

Pictured here is a Raspberry Pi 5 with optional PCB adapter to eliminate cables. The three ports (HDMI in, USB-C 5 V out, and USB-A for peripherals) provide all the board needs.

The CrowView Note is a pretty useful device for a workbench where one is often plugging hardware in for development or testing, because there’s no need to manage a separate monitor, keyboard, and mouse.

It is not a laptop, but attaching an SBC like a Raspberry Pi makes it act like one. The three ports conveniently located on the left-hand side (HDMI in, USB-C out for power to the SBC, and USB-A in for peripherals like keyboard and trackpad) are all that are needed in this case. Elecrow offers a “cable eliminator” PCB adapters to make the process of connecting a Raspberry Pi 5 or a Jetson Nano as simple as possible. The result is something that looks and works just like a laptop.

Well, almost. The SBC will still be a separate piece of hardware, whether connected by cables or by one of Elecrow’s PCB adapters. The result is OK for bench work, but especially in the case of the PCB adapter, not particularly rugged. Still, it’s a nice option and makes working on such boards convenient and cable-free.

Continue reading “This Is Not A Laptop, It’s A KVM Combo” →

Building A Paper Tape Reader To Read Bytes

August 19, 2024 by 19 Comments

Over at the Usagi Electric farm, [David Lovett]’s custom 1-bit, vacuum tube-based computer (UEVTC for short) has been coming along well the past years, matching and exceeding the Motorola MC14500B 1-bit industrial control unit (ICU) that it is heavily inspired by. What is still missing, however, is a faster way to get data into the computer than manually toggling switches. The obvious choice is to make a (punched) paper tape reader, but how does one go about this, and what options exist here? With a few historical examples as reference and the tape reader on the impressive 1950s Bendix G-15 which [David] happens to have lounging around, [David] takes us in a new video through the spiraling complexity of what at first glance seems like a simple engineering challenge.

Photodiodes in the tape reader of the Bendix G-15. (Credit: David Lovett, Usagi Electric)

Punched paper tape saw significant use alongside punched paper cards and magnetic tape, and despite their low bit density, if acid-free paper (or e.g. mylar) is used, rolls of paper tape should remain readable for many decades. So how to read these perforations in the paper? This can be done mechanically, or optically, with in both case the feedrate an important consideration.

Right off the bat the idea of a mechanical reader was tossed out due to tape wear, with [David] digging into his stack of photodetector tubes. After looking at a few rather clunky approaches involving such tubes, the photodiodes in the Bendix G-15’s tape reader were instead used as inspiration for a design. These are 1.8 mm diameter photodiodes, which aren’t super common, but have the nice property that they align exactly with the holes in the paper tape.

This left building a proof-of-concept on a breadboard with some incandescent bulbs and one of the photodiode to demonstrate that a valid logic signal could be produced. This turned out to be the case, clearing the construction of the actual tape reader, which will feature in upcoming videos.

Continue reading “Building A Paper Tape Reader To Read Bytes” →

An Open Source 6kW GaN Motor Controller

August 19, 2024 by 30 Comments

We don’t know how you feel when designing hardware, but we get uncomfortable at the extremes. High voltage or current, low noise figures, or extreme frequencies make us nervous.  [Orion Serup] from CrabLabs has been turning up a few of those variables and has created a fairly beefy 3-phase motor driver using GaN technology that can operate up to 80V at 70A. GaN semiconductors are a newer technology that enables greater power handling in smaller packages than seems possible, thanks to high electron mobility and thermal conductivity in the material compared to silicon.

The KiCAD schematic shows a typical high-power driver configuration, broken down into a gate pre-driver, the driver itself, and the following current and voltage sense sub-circuits. As is typical with high-power drivers, these operate in a half-bridge configuration with identical N-channel GaN transistors (specifically part EPC2361) driven by dedicated gate drivers (that’s the pre-driver bit) to feed enough current into the device to enable it to switch quickly and reliably.

The design uses the LM1025 low-side driver chip for this task, as you’d be hard-pushed to drive a GaN transistor with discrete components! You may be surprised that the half-bridge driver uses a pair of N-channel devices, not a symmetric P and N arrangement, as you might use to drive a low-power DC motor. This is simply because, at these power levels, P-channel devices are a rarity.

Why are P-channel devices rare? N-channel devices utilise electrons as the majority charge carrier, but P-channel devices utilise holes, and the mobility of holes in GaN is very low compared to that of electrons, resulting in much worse ON-resistance in a P-channel and, as a consequence, limited performance. That’s why you rarely see P-channel devices in a circuit like this.

Continue reading “An Open Source 6kW GaN Motor Controller” →