I decided to tackle something simple for my first attempt at etching a circuit board. I wanted something with a low parts count, and that was easy to test. I decided on a voltage level shifter circuit, as it only requires a MOSFET and 2 resistors per channel, and 4 channels is generally sufficient for most digital protocols.
I spent a day learning Eagle CAD, in which I created, destroyed, and re-created the circuit about 5 times. I ended up with a very clean-looking schematic, and two separate boards (both hand-routed); one for SMT parts, and one for through-hole. Both boards are really tiny; they easily fit on a breadboard.
Built for the Atomic Energy Research Establishment in Oxfordshire, it replaced work done by adding machines.
In November, it was rebooted, after a three-year restoration at the museum.
Design and construction of the 2m (6ft 6in) high and 6m (19ft 8in) wide machine known as the Witch, began in 1949.
The 2.5 tonne computer took up to 10 seconds to multiply two numbers but was reliable and often ran for 80 hours a week.
Kevin Murrell with the Guinness certificate Kevin Murrell: “Delighted” with Guinness World Records’ recognition
Kevin Murrell, one of the museum’s trustees, said: “This was at a time when computers weren’t really expected to work for more than five or ten minutes without breaking.
“Today the fully-functioning computer is proving invaluable in teaching our stream of educational groups about their computing heritage.”
Intriguing proof-of-concept experiment to demonstrate how to power a wireless sensor node via an energy harvester, from Crispytronics.com. Shared with us by Kris Barrett who wrote: “The energy harvester allows you to power low-power devices without batteries using ambient sources such as thermoelectric generators or solar cells. I think that it will be interesting to your readers/customers because it uses popular DIY components such as XBee radio modules, an AVR microcontroller, and a solar cell.”
From the project page:
This blog post has demonstrated one possible way to use the energy harvester to power a wireless temperature sensor. This blog post also demonstrated how to integrate an AVR microcontroller to monitor the power good (PGD) pin, pulse the secondary output enable (VOUT2_EN), and control the transmit frequency. Checkout the GitHub repository for the AVR source code and XBee configurations. Also, checkout the LTC3108 datasheet for more information related to the energy harvester. Finally, checkout the ATMEGA328P datasheet for more information about sleep modes and asynchronous timer operation using a watch crystal. Checkout the energy harvester product page for more information about the energy harvester breakout used in this project.
A few weeks ago I received a new batch of the AASaver PCBs at home. I thought, now that I am fairly experienced, it would be interesting to document the process of how I assembled the circuit boards. As you will see below, my assembly setup is manual and is nowhere near the capability of making more than a hundred boards at a time (for that I would outsource the assembly to a professional company). Still, it’s reasonably efficient such that I can enjoy the process of making without losing my mind or temper.
The 8085 processor uses a PLA (programmable logic array) to control much of the activity within the processor, such as instruction decoding and controlling the data flow between components of the chip. Pavel Zima has reverse-engineered the transistor-level circuitry of the 8085 microprocessor. I’ve looked into this in a bit more to figure out the architecture of the Programmable Logic Array, which takes up a large fraction of the chip. The PLA circuit is much more complex than the PLA on the 6502, for instance. It turns out that Pavel is ahead of me with information on the decode and timing PLAs, but the information below may still be of interest.
In this article, I show how overflow is computed in the 6502 microprocessor at the transistor and silicon level. I’ve discussed the mathematics of the 6502 overflow flag earlier and thought it would be interesting to look at the actual chip-level implementation. Even though the overflow flag is a slightly obscure feature, its circuit is simple enough that it can be explained at the silicon level.
It’s time to visit the topic of yield. This is a boring subject for many engineers, but for entrepreneurs, success or failure will be determined in part by achieving a reasonable yield. Unlike software, every copy of a physical good will have slight imperfections. Sometimes the imperfections will cancel out; and sometimes the imperfections gang up and degrade performance. As production volume ramps, these corner cases start adding up and a certain fraction of product ends up non-salable. In a robust design, the failing fraction may be so small that functional tests can be simplified, leading to further cost reductions. In contrast, designs sensitive to component tolerances will require extensive testing, and will suffer heavy yield losses. Reworking the defective units incurs extra labor and parts charges, ultimately leading to profit erosion.
Thus, a major challenge of moving from the engineering bench to mass production is re-designing to improve robustness in the face of normal manufacturing tolerances. This is called “design for manufacturing”, or DFM.
While I struggle day after day to read a seemingly infinitely small portion of Neal Stephenson’s Cryptonomicon on the subway each day, the folks at Numberphile whipped up this salient video that clearly explains the math behind the Nazi’s Enigma Machine.
I finally got my new tattoo yesterday. I’ve been meaning to get this done for the past two years, but being a nomad and being able to get appointments from good tattoo artist is a bit rough. Luckily Marcio Bornholdt at Blut & Eisen in Berlin had an open slot and was up for doing my tattoo on short notice, as I already had all the design files ready to go. There’s a ton here, despite the plain look.
The most obvious thing is the resistor color codes. Doing electronics for a living, that’s kind of easy to see why I would get such a thing done. However, that’s a very small portion of the population that will initially recognize it. Most people tend to see just the rainbow, and that leads to lots of fun questions. I’m openly bisexual, and have done queer geeks panels at both CCC-Camp 2011 and again at 28c3. So I’m fine with the ambiguity, which adds itself into the meaning of the tattoo for me.