Design Improvements on Versatile Turn Signal Flasher

We had turn signal flashers that that would misbehave from time to time, varying wildly, even though the math said it should work properly.  I investigated.

It turned out that the supply to the main timing IC, a bipolar 555 timer, was reliant on the drop across the turn signal flasher… which itself varied as the turn signal flasher turned “on” and “off”!  It was shorting out its own supply, essentially!  Oh boy.

I developed a circuit that would allow the 555 timer to still drive the monster output transistor, the TO-3 cased 2N5301, but hold the IC’s supply during the “on” time.  There were two problems with this – the circuit consumed too much current to be reasonably held up during the “on” time, and the output turned out to be referred to the wrong rail, in order to drive the output transistor using the same mechanism as before.

I addressed the current consumption by switching from the bipolar 555 timer to the then-relatively-new Intersil CMOS ICM7555.  What a joy that it ran on almost no current!

Then, I developed a 2-transistor output drive to replace the 1-transistor stage.  It worked well, until we ran it over temperature.  It was then that I learned one of the fundamental lessons that I’ve taken through my entire career: do not rely on one transistor to “short out” second transistor’s base drive over temperature!  It turned out that the Vce(sat) of the first transistor could exceed the Vbe(th) of the second transistor, sometimes, at low temperatures.

I found that you can short out the second transistor’s base drive, but then you need to put a resistor to the second transistor’s base, just to make it that much harder for the second transistor to turn on with leakage.

Well, that was a lesson learned, but then I just redesigned the stages to avoid that problem altogether.  Once bitten, twice shy!

I did do some preliminary work on using a MOSFET output on the flasher, but I couldn’t make the short-circuit protection work, and decided to stick with the bipolar output.  Later, a colleague, James White, took up that effort and successfully developed the “FET flasher”, which was another step forward turn signal flasher design.

Developed 36V Signal Flasher for Can-Car Rail

James White redesigned the “standard” 12 Volt turn signal flasher to use a MOSFET output, then he modified the design to successfully run on 24 Volts for bus & truck applications.

At about the same time that James was doing this, Can-Car Rail approached us to develop a 36 Volt flasher for their rail coaches.  I thought it would be easy!  Whoops, not so fast…

Well, oh my Lord, 36 Volts DC is nasty.  My first attempt to just use my modified 12 Volt design was a complete disaster.  The three lead-acid car batteries that we used for development just provided so much power that the 2N5301 output transistor overheated and failed on the first flash into a short.  The 12V and 24V designs could flash into a short indefinitely (Ed Van Humbeck drove around with a flasher wired directly across his car battery for about 6 months in 1980/1981 to prove that it could easily handle it).

The FET Flasher didn’t perform any better.

Instead, I had to develop a completely different design, right from scratch.  I used some of the same concepts, although I had to change components – the 2N5301, for instance, is only rated for Vceo to 40V, so it had to be changed.  The supply to the 555 timer had to be modified to handle the high voltage.  The drive stages had to be changed to handle the voltage translation and the drive requirements of the new output transistor.

The biggest change was that the 36V flasher got a “ground return connection”, which allowed it to be constantly powered, instead of having to scavenge the operating current from the bulb current.

We had to change the mechanicals as well – the original 12V and 24V flashers were simply placed into a plastic cap along with a heatsink/mount made of a piece of bent & punched aluminum, then the cap was filled with epoxy.  The But, like all challenging designs, it was 36V flasher needed much better heat dissipation for several devices, so it was designed as a flange mount device, a circuit board mounted on top of the “W” shaped metal mount, then covered with a lid.

The design was a challenge, the result was a success, but we didn’t make many units – perhaps a few hundred.  But, that’s the difficulty – you can’t tell ahead of time, what will be a winner, and what will be a loser.  You just have to do your best, and take on the ones that look reasonable.

Developed Fuse Panel and Turn Signal Modules for Ford New Holland “P53”

Ford New Holland had purchased Versatile Farm Equipment, brought some new products to the plant, and Vansco was providing much of the electronics that went into all of its tractors.

A new tractor was being made, which at the time was called “P53”.   It needed a power distribution panel / fuse panel and turn signal flasher.  I suggested that it could be a monster printed circuit board, and was asked to make it happen.

To accommodate differing standards worldwide, the turn signal flasher was a separate, small circuit board that plugged into a connector in the middle of the board.

Meanwhile, the main board was developed to fit inside one of the vertical window pillars.  It was physically large surface area, and had a large metal bus bar down the middle to distribute power to the fuses.   Of course, it had monster copper on it, 2 oz, and wide tracks, to ensure long life.

Implement IRIG-B Decoder in LINUX and on EFM8UB2 Universal Bee

I’ve been advised that one of the biggest challenges in the installation of power utility relays & recorders can be the setup and configuration of the IRIG-B time code distribution.

If there was a small, inexpensive hand-held device that could read the IRIG-B signal, and tell us all its characteristics – modulated/unmodulated, true/inverted, IEEE-1344 extensions active, time zone, offset, and other information – then it would be easier to diagnose the problem and tell the customer what they have to do to get the time sync to work.

I did a search and could not find anything… so after playing with decoding IRIG on my LINUX computer, I bought my own EFM8UB2 Development Kit and proceeded to write a decoder for it, per my blog entry.

The challenge now is to do a user interface for it.  I can easily do a LINUX UI (and did!), but what would be really cool is to (say) have an Android app that could connect to the EFM8UB2 using USB OTG – and display the data there.

I actually go the full Google Android SDK and emulator up & running, and was clicking along, learning the development of Android apps, but then along came Eye on the Ice – which took all of my spare non-work hours time.  One hobby at a time!  I’d like to return to it, and finish, some day soon.

Develop ERLPhase 2nd Generation DC Analog Isolation Module

The original DC isolation module, developed under my direction around 1999, used an unconventional custom off-line power supply and four Analog Devices AD204 isolation amplifiers, to provide isolated voltage and current input from DC to about 1 kHz.  This opened up a new market for recording sensors and telemetry signals on the TESLA, as well as some unique DC-level-sensitive AC applications, such as internal levels in static VAR compensators (SVCs) and DC converters.

Modern applications are much more stringent, however, needing better performance than the AD204 can provide (accuracy, noise level, and isolation), and the power supply couldn’t meet today’s restrictive EMC requirements.
So, I was asked to develop a newer high-performance DC Isolation Module. The basic concepts had been established by Steve Peddle, but he was quite busy on other projects.

The original concept was to perform “intelligent” ADC conversion on isolated “islands”, encoding the data in a protocol, and transferring the multiple streams of this protocol using digital isolation devices back to a central location, where it would be converted back by multiple DAC conversion on a circuit not isolated from the TESLA recoreder (as is required by the TESLA analog front-end).

I came across a potential alternative in the form of isolated sigma-delta modulator converters like the Analog Devices AD7401, which could give a highly accurate, flexible solution. Using an evaluation board, I captured data and performed extensive data analysis in Python.  I implemented the sinc3 filter in Python, demonstrated the trade-offs, and explored the possibilities of various configurations.

I evaluated the technologies against each other and wrote a report. After discussions with Steve and ERLPhase management, we decided to proceed with the sigma-delta modulator approach.

We obtained the evaluation kit for the Silicon Labs Universal Bee MCU EFM8UB20, and wrote the initial code as proof-of-concept and to bring up the system, handing it over to the firmware development team to implement the core functions.

I developed and documented the isolation plan, which included double 300V isolation gaps. After a design review, I created the schematic, and had two interconnected PCBs developed. I wrote a verification & validation document with guideline for the firmware implementation.

Elecsys starts with a… Last Call?!?

Elecsys started out with what could have been a “bang”, but ended up being a “whimper”.  My “whimpering” from lack of sleep!

Two businessmen from the Riding Mountain area, Terry Ledoux and Rene Roncin, contacted Vansco about development of an remote controlled duck decoy animation system.  Vansco was too busy, so they referred them to Elecsys.

Terry Ledoux was a taxidermist based in McCreary MB, who sold his taxidermy business and went full time into being an outfitter and hunting guide.  He wanted his new product to be called Last Call, a trade name which he owned.

They had started the development, even had nice rotary moulded enclosures made, but they didn’t know how to do the electronics, so Elecsys took them on.

Elecsys was actually operating out of the attic of Jason’s house.  We brought in all our contacts on the job – mechanical development, PCB layout, PIC programming – and ran our credit to the limit to cover all the costs of parts, etc.

The last 48 hours were an absolute nightmare.  We worked non-stop, had all kinds of issues – not the least of which was destroying multiple radio modules – they were not only quite expensive, but we also only had so many to work with.  I so much needed sleep that I went downstairs to lay down on the couch, while one of my colleagues was going to try to commission another unit with our last radio module… when I had a flash of insight!  I had to rush back upstairs and stop them from powering it up!  The radios had been destroyed by inductive kickback from the motor drive circuit, which operated from the same supply.  We hastily reworked the circuit, and with another 14 hours of work, we delivered two functional prototypes to the customer for a business trip to demonstrate them to Cabela’s in the US.

In the meantime, we were all strapped for cash – the customer, Elecsys, Jason and I ourselves… and had to settle for only a portion of the planned amount.  We did cover our costs, but not much more.  Needless to say, the customer didn’t proceed with the next stage of the development, which would have cost a lot more money.  That was unfortunate, because it was a cool product with a cute name, and I think it would have been a winner.

Some time later, we sat around with Ed Van Humbeck and discussed our experience.  He shared with us that something similar happened to him in the early days of Vansco, and counselled us to always get as much as possible up front – to at least cover the bare costs of the project, should the final payment not be forthcoming.  We still had much to learn!