Analyzing the vintage 8008 processor from die photos: its unusual counters


Ken Shirriff writes:

The revolutionary Intel 8008 microprocessor is 45 years old today (March 13, 2017), so I figured it’s time for a blog post on reverse-engineering its internal circuits. One of the interesting things about old computers is how they implemented things in unexpected ways, and the 8008 is no exception. Compared to modern architectures, one unusual feature of the 8008 is it had an on-chip stack for subroutine calls, rather than storing the stack in RAM. And instead of using normal binary counters for the stack, the 8008 saved a few gates by using shift-register counters that generated pseudo-random values. In this article, I reverse-engineer these circuits from die photos and explain how they work.

More info at Ken Shirriff’s blog.

A Solid State QRP Rig from 1955!

pics-Solid State QRP Rig

Pete Juliano, N6QW,  built his own vintage 1955 Solid State QRP Transmitter using the Philco SB-100:

Recently my friend Bill, N2CQR posted data on his blog ~ about a vintage late 1950’s early 1960’s 10 milliwatt 10 Meter transmitter. That was quite a feat!
But given my Italian heritage I could not let that pass without building my own solid state transmitter using a transistor from 1955. My rig operates on 14.060 and produces 0.4 milliwatts with a 3 volt collector supply using a Germanium transistor from Philco. The SB-100 was one of the first RF transistors that could work all the way past the 10 Meter band. The max Pout was 10 milliwatts –so mine is just loafing along.

More details at N6QW Homebrew Radio blog.

Check out the video after the break.


Analog Discovery USB isolation



Bob writes:

Back when I was deverloping the PSU burner, I wanted to have the Analog Discovery isolated from the common ground, to avoid noise and other issues. Since I did not have a way to do this, I ended up using a laptop on battery for measurements. But for long term, I needed to have this isolation. Unfortunately, things that can isolate USB at 480Mbps or faster are too expensive to justify.
The solution
The ADUM3160 isolator can provide a magnetically isolated 12 Mbps connection, which proved to be good enough. I grabbed one ready made isolator module from ebay for about $12, cheap enough. Well, it is not perfect: the B0505S DC/DC converter provided can only supply 1W and the Analog Discovery is a hungry beast.

More info at

App note: Selecting coupled inductors for SEPIC applications


Application example from Coilcraft on how coupled inductors gain advantage over separately wound inductors, calculations included. Link here (PDF)

The SEPIC (Single-Ended Primary Inductance Converter) topology is used in applications that require characteristics of both a buck and a boost regulator, specifically the ability to step up and step down the input voltage. Most often operated in CCM (Continuous Conduction Mode), SEPIC provides a non-inverted output voltage.

Typically, SEPIC is used in battery operated systems and automotive applications. In these applications, the battery input voltage, or bus line voltage, may be greater or less than that of the desired output voltage, depending on the charge state of the battery. The SEPIC topology can operate over more of the battery discharge cycle because of the ability to regulate the output voltage over a wider input voltage range, including above and below the output voltage.

The selection of one coupled inductor over two single parts saves board space and can also save cost.

App note: Choosing inductors for energy efficient power applications


Designing efficient power converters guide from Coilcraft. Link here (PDF)

In high frequency DC-DC converters, inductors filter out the AC ripple current superimposed on the DC output. Whether the converter steps the voltage down – buck – or steps the voltage up – boost – or both up and down – SEPIC, the inductor smooths the ripple to provide a pseudo-DC output.

For battery powered applications, battery life is extended by improving the efficiency of the entire power supply circuit, and inductor efficiency is often a major consideration in the design. Careful consideration of inductor efficiency can mean the difference between having your battery work when you need it and having to stop in the middle of an important task to plug it into a charger.

Inductor efficiency is highest when the combination of core and winding losses are the lowest. Therefore, the goal of highest efficiency is met by selecting an inductor that provides sufficient inductance to smooth out the ripple current while simultaneously minimizing losses. The inductor must pass the current without saturating the core or over-heating the winding.