Author: Al Williams

4504 Articles

Hubless E-Bike Is Nostalgic

December 16, 2023 by 12 Comments

[Chris Makes Stuff] is an aptly named channel. His recent video shows how he took a kid’s electric motorcycle toy and built a “penny farthing” bicycle. You might not know the bike by that name, but when you see it in the video below, you’ll recognize it. These Victorian-era bikes used a single large wheel before chain drives on a bike became a thing.

Of course, the big part of this — literally and figuratively — is the giant front wheel. There’s a second video showing how it was built in layers using wood.

Continue reading “Hubless E-Bike Is Nostalgic” →

Forget The Altair! Remember The Mark-8!

December 16, 2023 by 39 Comments

Calling any one computer the first hobby computer is fraught with peril. Most people think the MITS Altair 8800, first featured in Popular Electronics back in January 1975, was the first. Some might argue that others were first, but there is no doubt that the Altair started the hobby computer revolution from a practical standpoint. However, there was another computer that almost took the crown. It, too, appeared in a magazine — Radio and Electronics. But it was in the July 1974 issue. That computer was the Mark 8, and [Artem Kalinchuk] is building a replica that you can see started in the video below. This isn’t some Arduino work-alike. He has a pile of parts and some almost authentic-looking PCBs.

The Mark 8 used the 8008, not the 8080, so it was less powerful. [Artem] has been building a replica Altair, too. Check out his YouTube channel if you are interested in those.

Continue reading “Forget The Altair! Remember The Mark-8!” →

Inside Electronic Gain Control

December 15, 2023 by 18 Comments

Normally, if you want to control the gain of an amplifier, you’ll use a variable resistor. You know, like a volume control. But what if you want to control the amplifier’s gain with a voltage? [Engineering Prof] explains a circuit that can do this using a pair of op amps and a pair of matched JFETs.

The analysis is simple because you assume the op amps are not in saturation, so you can assume that the op amp will do what it needs to do to make the input terminals equal. The left-hand op amp has one input grounded, so the output will drive the first FET  to ensure the negative terminal is also 0V. It is easy to see that the current through R1 must then be the current through the FET, which is going to be the control voltage (which is negative) divided by R1.

Continue reading “Inside Electronic Gain Control” →

Repairing An HP Power Supply

December 15, 2023 by 3 Comments

One of the interesting things about living in modern times is that a confluence of the Internet and rapid changes in the electronics industry means that test gear that used to be astronomically priced is now super affordable. Especially if, like [Frankie Mashockie], you can do a little repair work. He picked up an HP6038A power supply for $50. We couldn’t find the original list price, but even refurbs from “professional” sources go for around $800. However, the $50 price came with a “for parts” disclaimer.

The power supply is autoranging. You usually think of that as a feature of meters. In a power supply, autoranging means the device can adjust the voltage based on load as you can see explained in the video below.

Continue reading “Repairing An HP Power Supply” →

Quick Negative Voltage For An Op Amp

December 14, 2023 by 30 Comments

It is a classic problem when designing with op amps: you need the output to go to zero, but — for most op amps — you can’t quite get down to the supply rail. If your power options are a positive voltage and ground, you can’t get down to zero without a special kind of op amp which might not meet your needs. The best thing to do is provide a negative supply to the chip. Don’t have one? [Peter Demchenko] can help. He uses a simple two-transistor multivibrator along with some diodes and capacitors to generate a minimal negative voltage for this purpose.

The circuit is simple and only produces a small negative voltage. He mentions that into a 910 ohm load, he sees about -0.3V. Not much, but enough to get that op amp down to zero with a reasonable load. Unlike other circuits he’s used in the past, this one is efficient. With a 5-volt input, it draws less than 1.5 mA.

Continue reading “Quick Negative Voltage For An Op Amp” →

The Nintendo Switch CPU Exposed

December 14, 2023 by 8 Comments

Ever wonder what’s inside a Nintendo Switch? Well, the chip is an Nvidia Tegra X1. However, if you peel back a layer, there are four ARM CPU cores inside — specifically Cortex A57 cores, which take up about two square millimeters of space on the die. The whole cluster, including some cache memory, takes up just over 13 square millimeters. [ClamChowder] takes us inside the Cortex A57 inside the Nintendo Switch in a recent post.

Interestingly, the X1 also has four A53 cores, which are more power efficient, but according to the post, Nintendo doesn’t use them. The 4 GB of DRAM is LPDDR4 memory with a theoretical bandwidth of 25.6 GB/s.

The post details the out-of-order execution and branch prediction used to improve performance. We can’t help but marvel that in our lifetime, we’ve seen computers go from giant, expensive machines to the point where a game console has 8 CPU cores and advanced things like out-of-order execution. Still, [ClamChowder] makes the point that the Switch’s processor is anemic by today’s standards, and can’t even compare with an outdated desktop CPU.

Want to program the ARM in assembly language? We can help you get started. You can even do it on a breadboard, though the LPC1114 is a pretty far cry from what even the Switch is packing under the hood.

Porting CP/M To A Z80 Thing

December 13, 2023 by 13 Comments

It is hard to describe the Brother SuperPowerNote. It looks like a big old Z80-based laptop, but it says it is a notebook. The label on it says (with lots of exclamation marks) that it is a word processor, a communications system, a personal scheduler, and a spreadsheet organizer. Brother also promises on the label that it will “Increase your power to perform on the job, on the road or at home!” Plenty of exclamation marks to go around. The label also touts DOS or Windows, but [Poking Technology] didn’t want that. He wanted CP/M. See how he did it in the video below.

This is a very early laptop-style word processor with a floppy and a strange-looking screen. It also had serial and parallel ports, odd for a word processor, and probably justified the “communication system” claim on the label.

Continue reading “Porting CP/M To A Z80 Thing” →