Quick Negative Voltage For An Op Amp

December 14, 2023 by Al Williams 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.

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Bunnie Huang’s Shenzhen Guide Gets A New Edition – Written By Naomi Wu

December 11, 2023 by Jenny List 23 Comments

If there’s one city which can truly claim to be the powerhouse of high-tech manufacturing here in the 21st century, it’s the Chinese city of Shenzhen. It’s likely that few people don’t own something made in that city or with parts that have passed through companies in the legendary electronic component markets of its Huaqiangbei district.

For years now the essential introduction to this world has come in the form of [Bunnie Huang]’s Essential Guide to Electronics in Shenzhen, a publication that unlocks the Chinese-speaking maze of vendors. All paper publications eventually become dated though, and this guide is no exception, so we’re very pleased to see a new version is on its way. Better still, it comes courtesy of Shenzhen native and maker extraordinaire [Naomi Wu], whose video series on YouTube has opened up so many corners of her city for those of us thousands of miles away. We can’t wait to see what she puts in it.

It’s also very good indeed on another level to see [Naomi]’s involvement, as earlier in the year she had to curtail her social media output under pressure from the Chinese government. We miss her unique window into the wonders of her city, and aside from her online shop it’s been concerning to hear very little from her of late. You can hear her talking about the book in a promotional video below the break.

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New Part Day: Flush-mount Touchscreen For Retro PC Build

December 11, 2023 by Donald Papp 19 Comments

I recently had the opportunity to purchase an early version of a new display, and it happened to be just the thing I needed to make a project work. That display is the Elecrow 11.6″ CrowVision touchscreen slated for release in 2024. Preorders are being accepted on Crowd Supply.

I had an idea for a retro-inspired PC build that was just waiting for a screen like this. I’ll talk about the display and what’s good about it, then showcase the build for which it was the missing piece. If you’ve got a project waiting for something similar, maybe this part will provide what you need or at least turn on some new ideas.

What Is It?

The CrowVision 11.6″ 1366 x 768 touchscreen has an HDMI input, USB output for touch data, and accepts 12 V DC. It’s made to interface easily with a Raspberry Pi or other SBC (single-board computer).

Personally I consider a display like this to be the minimum comfortable size for using desktop type applications in a windowed environment. Most displays in this space are smaller. But aside from that, what helps make it useful for embedding into a custom enclosure is the physical layout and design.

Since I was looking for the largest display that could be flush-mounted in an enclosure without a lot of extra space around the display’s sides, it was just what I needed. The integrated touchscreen is a nice bonus.

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The Sol-1: A 16-bit Computer In 74HC Logic With C Compiler And Unix-like OS

December 11, 2023 by Maya Posch 15 Comments

Sol-1 system pictured from the front. {Credit: Paulo Constantino)

While the concept of a computer system implemented in discrete logic ICs is by itself not among the most original ideas, the way some machines are executed certainly makes them stick out. This is the case with [Paulo Constantino]’s Sol-1, which not only looks extremely professional, but also comes with a lot of amenities that allow for system development, including a C compiler and assembler, a Unix-like OS (in development), DMA, and a whole host of interfaces to interact with the system and peripherals (serial, parallel, IDE, etc.). Not to mention a SystemVerilog model and an emulator, all of which can be found on [Paulo]’s GitHub.

More photos and videos can be found on [Paulo]’s YouTube channel, as well as the Sol-1 website, which shows off the intricate wire wrap work on the back of each PCB. In terms of the ISA, there are 5 general purpose registers (one scratch) which can also be used as two 8-bit registers each. Most operations are supported, except for floating point. For future improvements and additions, Sol-1’s OS will get more features added, and the first major software to be ported to the Sol-1 should be Colossal Cave Adventure and similar text-based adventure (dungeon) games.

Binary Clock Kit Blips Again

December 10, 2023 by Jonathan Bennett 15 Comments

Back in 1978, the world was a bit different. There was no Raspberry Pi, no Internet, and not even an ESP32 to build projects with. And rather than order electronics kits from Tindie or Adafruit, [Dr. Francitosh] selected this binary clock with his mother from a catalog, and made the order via mail. Simpler times. The good Doctor, AKA [Greg Smith], was a young electronics tinkerer, and his mother wanted a good project-in-a-box to show off his skills. Thus, a Greymark Binary Clock was ordered and assembled. Then, sadly, the beloved clock crashed from its proud mantle position, doomed to never to blink or blip again. Or was it?
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Check Your Board: Call For Submissions

December 8, 2023 by Arya Voronova 41 Comments

As both beginning hackers and Silicon Valley investors alike keep discovering, there are a lot of differences between hardware and software. One important difference is cost of iterating over a design. In software, you can comfortably rerun your build process and push updates out near instantly to tons of users. In hardware, all of that costs money, and I do mean, it costs way more money than you’d want to spend.

When I see people order boards that could never work because of some fundamental design assertions, with mistakes entirely preventable, it hurts. Not in an “embarrassment” way – it’s knowing that, if they asked someone to take a look at the design, they could’ve received crucial feedback, pulled the traces on the board differently or added some components, and avoided spending a significant chunk of money and time expecting and assembling a board that has a fundamental mishap.

Every thing like this might set a beginner back on their hacker journeys, or just have them spend some of their valuable time, and we can do a ton to prevent that by simply having someone experienced take a look.

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Simple CMOS Circuit Allows Power And Data Over Twisted-Pair Wiring

November 21, 2023 by Dan Maloney 29 Comments

If you need to send data from sensors, there are plenty of options, including a bewildering selection of wireless methods. Trouble is, most of those protocols require a substantial stack of technology to make them work, and things aren’t much easier with wired sensors either. It doesn’t have to be that complicated, though, as this simple two-wire power-and-data interface demonstrates.

As with all things electronic, there are tradeoffs, which [0033mer] addresses in some detail in the video below. The basic setup for his use case is a PIC-based sensor — temperature, for this demo — that would be mounted in some remote location. The microcontroller needs to be powered, of course, and also needs to send a signal back to a central point to indicate whether the monitored location is within temperature specs. Both needs are accommodated by a single pair of wires and a tiny bit of additional circuitry. On one end of the twisted pair is a power supply and decoder circuit, which sends 9 volts up the line to power the PIC sensor. The decoder is based on a CD4538 dual monostable multivibrator, set up for an “on” time of one second. A trigger input is connected to the power side of the twisted pair going to the sensor, where a transistor connected to one of the PIC’s GPIO pins is set up to short the twisted pair together every half-second. Power to the PIC is maintained by a big electrolytic and a diode, to prevent back-feeding the controller. The steady 0.5-Hz stream of pulses from the sensor keeps resetting the timer on the control side. Once that stream stops, either through code or by an open or short condition on the twisted pair, the controller triggers an output to go high.

It’s a pretty clever system with very simple and flexible circuitry. [0033mer] says he’s used this over twisted-pair wires a couple of hundred feet long, which is pretty impressive. It’s limited to one bit of bandwidth, of course, but that might just be enough for the job. If it’s not, you might want to check out our primer on current-loop sensors, which are better suited for analog sensors but still share some of the fault-detection features.

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