Testing Nodic nRF51822 BLE SoC

October 12th, 2013

I have had a chance to test Nordic Semiconductor’s nRF51822 Bluetooth Low Energy system on a chip last week.  It reminds me of a TI CC2540 but with an ARM. Thoughts and test results in my nRF51822 post over on e14.

A $1126 Mistake

October 6th, 2012

For the past few months I rented a VNA from TRS Rentelco.  It was a nice $14,000 VNA, and they only charged $600/mo plus tax.  At the same time, I rented an HP 85033D cal kit.  I could have made my own, but I decided to get a nice one for $100/mo.

Eventually I made my own and tested it against the HP cal kit.  It worked.  So I stopped renting it and returned it.  A month later TRS Rentelco showed me how I had done $1126 in damage to the open portion of.  They sent me a picture showing the damage.

It sounded bogus.  It could have been that way when I got it.  I only mated it a few times with a factory-made cable.  It worked fine before I sent it back.  This all sounded bogus so I called my trusted friend and RF expert, Robb Peebles of LSR, to ask if this was a bunch of baloney.

Before I was done explaining what they were charging me for he said, “Was it on the open?  The opens are fragile.  I did you rotate the 3.5mm socket with respect to center pin on the mating connector.”  He went on to explain what TRS Rentelco explained: 3.5mm connectors are similar but not exactly the same as SMAs.  3.5mm are higher end and very fragile, especially if they’re the open on a cal kit.

So I guess TRS Rentelco was right.  I must have done damage to the open when I connected it to my cable.  I must have turned the open with respect to the mating connector instead of pushing them together and tightening the screw on the outside of the SMA.

So by turning something gently but in the wrong way, I did $1126 worth of damage to a part whose function is to do nothing.  (well, nothing at low frequencies anyway)  At the frequencies I was working at (1GHz), I could have probably done as well not using the open and just leaving the SMA unterminated and saved $1126.

Be careful with 3.5mm connectors.

CC430′s Core Is Powered By Built-In Switcher

January 27th, 2012

I have been working on some boards with TI CC430 processor + radio chips.  It amazes me how much is crammed into that part.  It includes a complete multiband transceiver with 10mW output.

The radio portion runs on 2V and a built-in linear regulator allows you to power it with 2.1 to 3.6V.  Since it’s a linear regulator, the current is the same regardless of the input voltage, so it pays to use the lowest input voltage possible.

Earlier this week I was working out a scheme to do this for the radio portion and the processor portion.  I thought I could save power by reducing the voltage to the processor, but it turns out the CC430 chip has a built-in inductorless switching regulator to power the processor core.  So if you lower the input voltage, the current increases leaving the power roughly constant.  This means the engineer using this part can use any supply within the allowed range without it affecting power consumption.

What more could they do to the CC430?  Could the next step be a switching power supply for the radio portion too?

Politically Motivated Attacks on STEM Workers

January 15th, 2012

Iranian scientist Mostafa Ahmadi Roshan was murdered apparently for his work on the Iranian nuclear program.  It is unclear whether it was an foreign covert operation.  It is possible the Iranian government is responsible for the attack intended to put the blame on Israel.  It was very unfortunate that an Israeli military spokesperson said he is “definitely not shedding a tear” over the murdered scientist.

This attitude of tolerance of violence toward scientists and engineers working on controversial project is completely unacceptable.  US should reevaluate its support for the Israeli government if there is evidence it condones this type of attack.

Iran claims its nuclear program is for peaceful purposes, but it is likely its goal is development of weapons.  It is understandable that the governments that have nuclear weapons want to keep their weapons but keep others from getting them.  This creates a perverse incentive for governments to want to join the nuclear weapons club.

Regardless of the politics, scientists and engineers should never be targets of violence for the programs they work on.  Eight years ago I casually talked to someone from the US nuclear weapons program about work for them.  They assured me the job was to control access to existing weapons not to develop new ones.  I suspect that was correct, although  found a different job and never learned any more about the nuclear job.  If I had worked on the project, foreign powers might have felt like I was military target, but they would be wrong.  Engineers and scientists have a responsibility to limit their work projects they believe are moral and ethical.  They should never be part of  geopolitical power games.

Photo from Fars News Agency/European Pressphoto Agency

Skeptical Toward “Neurological Conditions”

December 29th, 2011

The New York Times had a good article this week about two teenagers who are identified as being on the “autism spectrum”: Navigating Love and Autism.

The article was well written and held my interest, but it is really surprising that a case of geek love merits so much discussion.  It tells us how they “have trouble reading emotions and gauging social cues that others take for granted.”  It makes me  think of people who have trouble understanding the mathematical models and control loops in nature that others take for granted.

Consider some basic everyday mathematical abilities that some people lack:

  • Estimating distances, weights, and volumes within an order of magnitude
  • Distinguishing between open loop systems like a typical stove from close-loop systems like a typical oven
  • Taking into account that the coefficient of skidding friction on a slick road is significantly less than the coefficient of static friction
  • Ability to evaluate financial products such as mortgages or insurance agreements
  • Awareness that the levels of most medicines in the body decays roughly exponentially
  • Distinguishing correlation from causation

It’s easy to dismiss the lack of these abilities as idiocy.  It would be easy, although I’ve never heard it done in a mainstream article, to dismiss them as a neurological condition and write a cute article about the relationship troubles these foibles cause.

If we’re going to do label all idiosyncratic personality traits as conditions, hard-core salesmakers and politicians need a label just as much as hard-core engineers.  Probably everyone who’s hard-core about anything and goes out and changes the world could get a neurological label.  We’re supposed to have moved beyond this sort of thing.  We need to be skeptical of “neurological conditions” whose only symptom is minor odd behavior.

IEEE Benefits Bulletin Links to Questionable Banking Advice

December 18th, 2011

IEEE e-mailed a “benefits bulletin” last week.  I love IEEE and am an officer for the Madison, WI Section, but I have never found anything useful in the financial services IEEE promotes.  Of the non-officer snail mail I receive from them, most of it promotes insurance products.  Based only on their snail mail and discounting all the good stuff I do with them online and in person, IEEE feels like an insurance company promotion organization with a side focus on engineering.

The most recent e-mailing links to a US Bank website extolling the benefits of a good credit score.  Their argument goes something like this:

We’ve developed a scoring system for individuals’ trustworthiness when it comes to paying back money.  The way to score high is to use our product.  The benefit of scoring high is you can use more of our product.  Even if you don’t like using our product, the score is being used by other industries.  We’re hoping this number we created will become widely accepted as a general indication of trustworthiness in all areas of life.  So use our product!

That’s a great deal for them.  It’s no wonder some people feel such anger toward financial institutions.  That anger is unnecessary, IMHO, because banks are not as powerful as they fancy themselves.  Their scoring system is not widely accepted, except by banks and now insurance companies.

I am not categorically opposed to a single number that attempts to distill someone’s trustworthiness in paying bills.  I’m opposed to the banks FICO score, though, because a) the scoring method is not open to the pubic and b) much of it is self-servingly based on using their product.  I find this doubly offensive when it’s presented as tips for responsible financial management.

I am positive overall on the concept of finance and have encouraged engineers to go into the financial industry if they are so inclined.  When we deal with any company promoting a product and they say “How can I help you?” we are immediately cautious they’re trying to sell us something.  Financial institutions should be treated no differently.  IEEE should not present their propaganda as tips for responsible living.

Thermal Relief Error Costs 10dB

July 16th, 2011

A few years back my layout package omitted a thermal relief on the pad of an RF part placed with a ground pour.  The software is supposed to put small traces from the pad to a pour of the same net wherever it can.  For some reason, when I did a minor rev of this board, the software omitted one of the thermal reliefs.  This resulted in a pour ground connection on one of the two ground pads on an RF connector.

At DC this is fine.  At 2.4GHz the effect is negligible.  Between 5GHz to 6GHz, the error results in 8 to 10dB of signal loss.  If you simply scrape away a bit of the soldermask and bridge the pad to the pour, the footprint works perfectly.  It is amazing that that tiny mod results in 10 times the power being delivered to the antenna.

I suspect the reason for it has such an impact is the center conductor goes to a coplanar waveguide, i.e. a trace with grounds below it and on both sides of it.  The ground plane on the left side is connected to the ground on the right side through ground vias, but there is no path not through a via.  If there had been copper on the same layer as the connector connecting the two sides together, the missing thermal relief would not have mattered as much.

The cautionary part of this story is the length of the coplanar waveguide is less than 1 cm.  The fact that the length of the transmission line is shorter than the wavelength being transmitted does not make it immune to transmission line problems.  The entire path through the connector and connected coax is longer than a wavelength, and a discontinuity at one point can drastically effect power transfer.

This all happened years ago, but every once in a while someone new at the client asks me why we rev’ed this board, and I have to go over this infamous mistake.

Engineer Struggles to Understand IDEF0 and Process Modelling

May 19th, 2011

David Marca presented at today’s meeting of my local section of IEEE on the topic of modelling systems.  David’s focus is not on a modelling something like a filter or a channel but rather the context in which an enterprise operates.

If the team doing the work and the customer both understands the problem being addressed on a project, Agile Methods can handle the specification.  Usability Engineering is when someone on the team works closely with the customer to get feedback.

More complicated problems or problems that are new to the team and the customer can be modeled with a Universal Modelling Language (UML).  SADT/IDEF0 is one such method.

My understanding is SADT/IDF0 is a model of an asychronous state machine.  While it’s in a given state, the system acts as a time-invariant continuous-time system.  Every time the “state” changes, the transfer function of the time-invariant system changes.

I would love to hear feedback on whether my DSP-ish understanding is right.

TI Switcher Module Touts “Higher Efficiency than a Linear”

May 18th, 2011

This must be a case of a tech writer generating a product description after talking about the part to an engineer.

The part in question is a TI switching regulator module.  When you go to the PTH08080W product page, the second sentence you find is: The PTH08080W sources output current at a much higher efficiency than a TO-220 linear regulator IC, thereby eliminating the need for a heat sink.

This is like saying the car we’re selling is much faster than a flat-bar hybrid bicycle, thereby eliminating the need to carry a water bottle.

It’s bizarre that they compare their switcher’s efficiency to a linear regulator, which is the least efficient way to step down voltage.  The whole reason to use a step-down switcher is to avoid this inefficiency, so of course their part is more efficient.  It goes on to say this eliminates the need for a heatsink, which is sometimes true, although whether you need a heatsink on a linear regulator depends on how much power your dissipating in it.

My guess is TI figures most people go to the page to scan the specs and get the datasheet, so it doesn’t matter if the description makes sense.

AirFire Mobile: More Olive Tree than Lexus

May 14th, 2011

I love my Wisconsin-based mobile phone provider, AirFire Mobile, formerly Einstein PCS.

  • I can get through quickly to a Wisconsin-based employee when I have a question.
  • $35/mo for unlimited calling plus unlimited low-speed (64kbps) Internet access
  • They help you set up any phone you bought on E-bay just as eagerly as they help you with something they sold.

I have been having a problem using their service, though, when I’m in a certain area of Madison.  The phone signal indicator goes up and down as if it’s trying to link to several towers.  This drains the battery over several hours.  I cannot make a phone call from this area unless I move to higher ground, where apparently I gain line-of-sight to a tower that my phone can use.

The people at AirFire are still trying to work out why this is happening.  Yesterday I was on the phone with them about this issue, and I got disconnected.

Me: I got dropped while someone was helping me with an issue.
AirFire: Did you get his name?
Me: No, I don’t think he said it.
AirFire: Hmmm… Do you want to go over your problem again with me?
Me: He had faint accent.  I think he was from California.
AirFire: That’d be Charlie.  Let me get him.
She found the correct person and put him on the phone.

Borrowing Thomas Friedman’s metaphor, AirFire Mobile is much more Olive Tree than Lexus.

I hope they can solve my problem because I think it’s something idiosyncratic, not necessarily a flaw in AirFire’s system.