Charles J Gervasi

Dave and Chris of the Amp hour asked on their last show whether technology will eventually cause a shortage of jobs.

If computers could replace almost all human jobs, it would be a good thing because that would mean we could have the same goods and services we have today without human work.  This is something people have dreamed about since time immemorial.

When the industrial revolution started, it meant people theoretically could work much less and have the same lifestyle they would have had in agricultural economy.  They could spend the rest of the time relaxing with their families.  Instead, though, society chose to keep working and produce way more goods and services.

Something similar happened when we went from a hunter-gatherer society to an agricultural society.  We may be seeing something similar today going from an industrial society to an information/automation society.  If it plays out the same way, the amount of goods and services we can produce will continue to increase.  We are right to be asking the big questions of how we want that go forward and what we want to do with our new-found production capabilities.

My first job was at a small private company.  They were frugal about spending money on tools.  I recall being frustrated at having to spend time wandering around looking for tools.  I had a notion to bring my own tools, but my colleagues told me it wasn’t a good idea because with tools in short supply they would be easily lost to well-meaning people who would borrow them and forget to return them.  The company eventually bought me new tools, provoking some resentment from other employees who didn’t have new tools.  I had no idea at the time that the on-the-job training I was getting in circuit design and debug was worth way more than the cost of some tools and books.

In retrospect, I can’t imagine why I didn’t use my own tools.  Even at a company that is short on tools, if you keep them in a locked toolbox, they’re not likely to be taken.  A very nice set of electronics tools can be had for under $1,000.  That is a modest amount for an engineer.  Even for people working at full-time jobs that claim to provide everything an engineer needs, engineers are still paid for getting things done.  The employer may not notice time wasted searching for tools, but that time is money/experience lost to the engineer who could be using that time to design new technologies.

All engineers make their money by causing things to be worth more than the sum of their parts.  Tools and books are a cost of being an engineer.

An IPC cleanliness designator (defined in IPC J-STD-001) is sometimes called out on assembly drawings.  A common designator is C-22.

The first number indicates the number of board sides that must be cleaned
0 – No cleaning required
1 – Solder side only must be cleaned
2 – Both sides of the board must be cleaned.

The second and following numbers define the types of cleanliness tests to be performed:
0 – No test for cleanliness required
1 – Test for rosin residues – Used when high solids rosin fluxes are used in assembly.
2 – Test for ionic residues – This is a basic inexpensive test to detect insufficient cleaning.
3 – Test surface insulation resistance (SIR) – This test exposes the assembly to high temperature and humidity to accelerate failure mechanism that lead to shorts.
4 – Test for other organic contaminants – Type and amount of residue is measured, usually using a spectrometer.  This is an expensive test.
5 – Other tests requested by client – Any other testing beyond tests #1 – #4.

It is permitted to call out any combination of test types.  If both sides are to be clean and all tests to be performed, the cleanliness code would be C-212345.

Part of learning engineering is learning what requires precision and learning to let go and be imprecise when necessary.

I recall being in Dr. O’Malley’s circuits class at the University of Florida in the mid 90s. He drew an op-amp on the board and said it’s a very high-gain differential voltage amplifier. Someone asked what gain we should use. He said, “You can use whatever big number you want. For this example let’s use, I don’t know, say a million.” Several people laughed thinking it was a joke. O’Malley didn’t appear to understand the laughter. He continued, “You could use a similar number like two hundred thousand or five million. Anyway, that’s not the point. I hope it’s obvious that…”

I was amazed that 200,000 and 5,000,000 were very similar for the purposes of understanding an op-amp, so amazed that I remember it 15 years later. The statement seems perfectly natural now. Engineering has changed my mindset on precision.

This mindset affects aspects of life completely outside of engineering. The other night my wife, who is an attorney, said our baby was 10 minutes away from needing another dose of Tylenol for teething. “10 minutes?” I asked, “The tolerances can’t be that tight. That’s only a few percent of the dose duration.”

“It says 80mg every four hours” she said matter-of-factly, as if quoting the Uniform Commercial Code.

“But it doesn’t give a tolerance. I bet if you plotted the half-life of Tylenol in population of healthy babies, you’d find a distribution with half-lives varying by more than an hour. Even accounting for that, different babies will experience a therapeutic response at different blood concentrations.”

She said she felt more comfortable with a very clearly defined rule. Those tolerances made her uneasy. I felt more comfortable with a system that does not depend on any element having very tight tolerances. I wonder to what extent similar professional mindsets affect the daily lives of people in other fields such as accounting, medicine, science, teaching, and so on.

I had another run-in with “quasi-bidirectional” ports today.  As on the last project where I encountered them, they caused confusion.  Today’s encounter was with the PCA9501 I/O port chip.

They should be called “open-drain outputs with moderate pulls connected to an input”.

They are open-drain outputs and can only be used as input ports by writing a logic high and then reading.

The thing that makes them tricky is the built-in pullup in moderately strong.  In the circuit I encountered today uses a quasi-bidirectional port as an output to drive the base of a ‘3904.  The moderately 100uA pullup is enough to drive the transistor, but I would have to crunch some numbers to know if will work in this circuit over the entire range (the low end) of beta values for a ‘3904.

Adding exteranl pullup is an easy solution in this case because this board’s power budget is not tight.

The tricky part is that quasi-directional ports have a read/write bit, giving the user the impression that it functions as either a push-pull output or a standard input.  The port’s ability to source some current furthers this misconception.

A project involving high-power radios powered by PoE prompted me to look into the maximum power you can get from PoE.

IEEE 802.3af PoE – 15.4W max power
IEEE 802.3at PoE+ – 25.5W max power

Both types of PoE can be Mode A or Mode B.

Mode A – Power delivered on TX/RX pairs
Mode B – Power delivered on spare pairs

TI has a circuit to run Mode A and B simultaneously, resulting in a maximum power of 51W. The implementation is tricky because it must balance the current so that neither Mode A or B lines exceed the maximum current.

I would love to hear from someone who has implemented 51W PoE or used other cheats to get > 25.5W over Ethernt.

In the past, I used three value-ranges of decoupling on high-speed designs:

• Bulk: A 10uF or two caps located anywhere
• Intermediate: Some 0.1uF caps located near the part
• High-frequency: Some 1000pF located right under the BGA or connected to the power pins directly

You could not get high-value ceramics in small packages, so you had to use low-value capacitors to get the low inductance associated with a small package.

Now 0.1uF ceramics in an 0402 package are a standard low-cost part. I recently had a notion to check the curves to see at which frequencies a 1,000pF 0402 had a lower impedance than a 01.uF 0402:

There is only a tiny frequency range where the impedance of a 1,000pF is better. I would be interested to hear from anyone who knows a good reason to use them low-value decoupling caps today.

G. Pascal Zachary says, in his article for IEEE Spectrum Magazine, Why Engineers Must Try to Save the World, that engineers need to work to save the world.

It may be selling engineering short to call the desire to save the world  “messianic”.  The end of the article focuses on geoengineering approaches to climate change.  The article discusses debate within the UN about whether we should not study geoengineering approaches to climate change or we should proceed in case the planet is “broken beyond conventional means of repair”.  It’s questionable to call a complex system like our planet “broken” or fixed”.  There certainly are no conventional means of repairing a planet.

The climate of the earth is changing because of natural processes (i.e. moving deeper into a glacial minimum period) and because of human activities.  Critics of geo-engineering want an approach based on carbon emission reduction and increasing natural CO2 absorption.  I support those measures, but I suspect they will be insufficient.  Even if we stopped all carbon emissions, we would still face rising sea levels due to the natural receding of the glaciers.  The goal should not be a planet just as it would be if humans were not present but a planet that serves human needs.  Engineers need to be a part of that.  The fact that climate change is happening faster because of human activities only increases the urgency to develop geo-engineering techniques.

This research will be hard to promote because the loudest voices in the environmental debate either want a) to preserve a climate free from anthropogenic effects for the sake of nature itself or b) to deny blissfully that the climate is changing and human activities can shape how it changes.

The problem of sound engineering approaches being tough to sell crops up in other issues.  Engineers should work on promoting engineering-style solutions to the world’s big problems.