PCjr 25 years later

pcjr

[Trixter], connoisseur of old hardware, is celebrating the 25th anniversary of the PCjr. IBM’s PCjr was killed only 18th months after being revealed and [Trixter] lays out exactly why. Overall, it was designed to be cheap to produce and sell, but many of the choices made it difficult to use. They used the CPU instead of DMA for floppy access; cheaper to make, but you couldn’t do much during disk reads because of it. The video memory scheme left little room for programs that could take advantage of it. It also had compatibility issues that made IBM clones a more attractive choice. [Trixter] ends by pointing out that some good came of it when the Tandy 1000 copyied the good ideas while leaving out the restrictive memory issues. He recommends Mike’s PCjr Page for more information on this classic machine.

Adjustable breadboard power supply

psboard

This looks like a great addition to your breadboard. [Nerdz] wanted a power supply that was easily portable and adjustable. He built a custom board that plugs directly into the breadboard’s power rails. It has a pot attached to the ground of a 7805 voltage regulator so the output can be adjusted from 5V to just under the supply voltage. Anything that makes a breadboard less of a rats nest is definitely a good thing.

Business card AVR board updated

bcard

Evil Mad Scientist Laboratories has updated their business card AVR breakout boards to version 1.1. We suspect the changes will probably make them even more popular. The boards are designed for the ATmegaXX8 family of microcontrollers. The center has all 28 pins labeled while either end has a prototyping area. An in-system programming header is also provided. For the new version, both prototyping areas have been increased to accommodate DIP14 packages. The holes for the microcontroller are now larger so that they can hold a ZIF socket. Finally, the power and ground traces have been expanded. We’ve always like the versatility of these boards, as demonstrated in the Tennis for Two project, and can’t help wondering if these updates were made to facilitate another project.

Stripboard Drawdio

drawdio

When we posted about the Drawdio release, mentioned how simple the circuit was and that we wouldn’t be surprised if people adapted it. [Dylski] decided to build it using stripboard and parts he had laying around. He shows how he laid it out on paper so that it would fit on a 29×5 piece. It took some planning, but the end result is a perfectly functional as you can see in the video below. [Read more...]

Design for manufacture

sparkfun

SparkFun has posted an excellent guide to the many different issues you could run into when you finally decide to get a circuit board professionally produced. We assume that most of you aren’t running a professional design firm and will appreciate these tips gleaned from years of experience. They provided a rule list, Eagle DRC, and CAM file to help you get it right the first time. The end goal is designing a board that won’t be prone to manufacturing errors. The tutorial starts by covering trace width and spacing. They recommend avoiding anything less than 10mil traces with 10mil spacing. For planes, they increase the isolation to 12mil to avoid the planes pouring onto a trace. They also talk about annular rings, tenting, labeling, and generating the appropriate gerber and drill files. SparkFun isn’t completely infallible though, and manages to produce a coaster from time to time.

SparkFun naturally followed up this strict tutorial with a guide to unorthodox header hole placement. If you want to learn more about Eagle, have a look at [Ian]‘s overview of Eagle 5 and Ruin & Wesen’s layout videos.

Nintendo DSi teardown

dsi_teardown

[bunnie] managed to pick up a Nintendo DSi while in Japan. It seems he had the device running less than an hour before he tore it down for an impromptu hotel photoshoot. There’s nothing too surprising and he mentions that the CPU certainly feels more capable than the previous model, which may explain the shorter battery life. The ARM processor sits under an RF shield directly below the WiFi card. The best photo is the top side of the board with every single debug point labeled in plain English on the silkscreen. We’re sure that’ll help with the development of new homebrew hardware.

[bunnie] has posted some interesting teardowns in the past. Have a look at his Sony XEL-1 teardown to see the inner workings of an OLED TV.

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