Tomorrow's visit to customer site to fit and test a prototype of a device that cuts the power consumption and improves reliability of some items fitted to vehicles, has been cancelled due to lack of available test vehicles.

This is actually good, because although it seemed as if everything was going to plan, and indeed, the part that is assembled works exactly to specification, there is more to do than I could complete today. I need to make the very first prototype of a debouncer that should prevent the doors being logged as opening and closing at one second intervals, but also a pulse stretcher to allow the processor to have time to log the engine start (Don't ask!) I did the paper design about ten days ago, and now I have all the parts, there *should* be no surprises, except for how long it takes to solder it all together tidily.

There is up to another four hours work to do before it is all ready for use.

The new test is scheduled for Friday, but three hours drive away instead of locally. You win some, you lose some. At least I can visit muuranker the night before, and be already half way there in the morning. I wasn't looking forward to getting up at 05:30...

... brighter than a thousand suns - or at least, as bright as a 400W metal halide lamp.

For about the last 3 weeks, as well as other ongoing tasks, I have been working long hours on designing parts of the first prototype of a luminaire that is intended to be as bright as a 400W metal halide lamp, though the one model we tested only consumed 150W of electricity. Photometry, to be carried out by the prospective end user, will discover if the intended light output is reached, but it is very likely, because the overall designers of the luminaire have done the maths, and consulted optical designers.

It was too bright to look at, even wearing sunglasses.

There are seven LED printed circuits, each with two series strings of 12 white LEDs, independently dimmable. The LED strip is made on a type of printed circuit consisting of a thick aluminium substrate (to carry away the heat from the LEDs), with a very thin insulating layer, of a material chosen to be thermally conductive, and with the copper tracks etched on top of that. There is only one layer of connections, which makes the design difficult, but this composite material is needed to remove the heat from the LEDs. They are specified to lose only 20% of their light output over 60,000 hours if run at the maximum specified temperature, but above that level, the reliability declines rapidly.

Energy savings alone might not render this product cost effective, but when the close to zero maintenance costs are included, it should be very good in its intended use (initially fuel station canopies). In real use, the lighting is likely to last until the building is subject to major maintenance or remodeling.

This was an interesting project to work on, but had a difficult deadline, because the requirement to deliver all the electronics for three units was brought forward by 6 weeks. I predicted and avoided one electrical problem associated with the unusual PCB material for the LED strips, but had to retrofit extra parts to correct for another one (very high capacitance between LED and substrate). It was a first prototype.

The (switchmode) electronics to dim and control the current in the LED strips is on the same PCB as the LEDs, but is very constrained because most of the area is covered with reflectors, so that parts more than 3mm thick can only be placed in an 8mm strip at one end of the long narrow pcb. It is for this reason that the capacitance between the LEDs and the substrate was an issue. Had it been possible to fit the inductors in the ideal place, the capacitance would have been irrelevant.

The control and comms electronics is on a 21mm wide pcb that plugs into all the LED strips and carries power and control signals from the processor to control brightness, measure temperature, and so on. That contains, among other things, a memory chip carrier 19mm wide, so I had to design it with four layers. Even the on-board switchmode regulator worked cleanly, which is good because there was no time to make a revised control pcb.

It is done for now, finished yesterday evening, and I will not know if the project is to proceed for about a month. Now to catch up with the major backlog of other tasks. If anyone is expecting any kind of response from me, and I don't catch up soon, please remind me, because I have not been noting everything while concentrating on this project.

I spent most of my day working as a counsultant for a company with offices in Milton Keynes, at their offices and at one of their suppliers. I discovered a number of problems on the electronics they were being supplied with, much of it at the pre-production sample stage. Bullet dodged, from their point of view.

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After being stuck for some time on the problem of stabilising the control loop for the battery charger, I may now have found a workable answer. Yay!

Though it was tricky to do so, I modeled it in a simulator, and the graphs of phase and gain were so much better than hand drawn sketches that I was able to find an answer.

Now for some belated sleep, before the rest of the weeks work, for which I would have preferred four days, to allow for purchasing the necessary parts to upgrade a prototype power supply from 110W to 200W.

Since the middle of last week, the main task I have been working on is to stabilise the voltage control loop of a switched mode battery charger. The design is slightly more complex than some, because the output voltage can be both above and below the input - so it uses a sepic converter. Not a big deal, but slightly more difficult to control. The control loop oscillates over a range of 0.2Hz to 500Hz, depending on the components fitted to attempt to stabilise the loop. The one thing it won't do is work in a stable and accurate manner.

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On Thursday morning I received an appointment letter for the x-ray I need for my right shoulder. Once the x-ray is done, next Thursday morning, I should be offered a physiotherapy appointment. I still wish it was happening more quickly, because the available movement without severe pain is gradually becoming more restricted, but at least there is some progress. Now I can angle my arm maybe 20° out from my side, more than that forwards (and not backwards at all) before it is too painful to move further.

The pain was worse at the beginning lf last week, though, because, for a while, there was no pain free position, and it was rarely less than excruciating.

In other news, I have a short term, but demanding, power electronics project to work on. I get to design the power electronics for a high power LED lighting system, that is designed to save considerable energy compared with the system it is to replace. Getting sample magnetic components quickly enough to assemble a prototype in time to meet the deadline is likely to be one of the more difficult aspects.

When anything technological fails, I am inclined to take it apart and attempt to repair it. Sometimes it is not practical, sometimes I don't have all the necessary knowledge, but more often than not I have succeeded. BUT, things have occasionally turned into an epic, so in recent years, I have tried to temper the tendency to fix everything myself with a policy of paying for repairs for things which the full time repair person can do much more efficiently.

This has worked for car repairs, because it doesn't take a lot for someone to do it more quickly than I do. I can get down on the ground under the car fairly easily, but, increasingly, standing up again afterwards is difficult and I need a rest. All the right tools to hand, and a hydraulic ramp, not to mention the practice of doing the job, wins most of the time.( Cut for length )

This is relevant to the latest repair; rustica's laptop computer. Months ago she asked me about something inside rattling, and I told her that it was probably the heatsink from the graphics chip (which turned out to be true) but that because it was still under warranty, it would be best if I didn't fool with it.

A couple of days back I removed the easily removable covers underneath the computer, now out of warranty, to find out if it had a place where an internal wireless card could be fitted. No such luck, but I found the heatsink from the graphics chip wedged in the air outlet from the processor cooling assembly. Come the warmer weather, it would have kept crashing, if it did not fail completely. It was the most difficult laptop to dismantle that I have found so far, but there was no point in paying a repairer who had not fixed the problem previously, to make a pigs ear of it again.( Cut for length )

I can't quite see how people who don't have a good idea how most of the technology they use works can avoid ending up throwing away and replacing things which fail, no matter how small the fault. Thus the volume of waste to be buried or recycled grows. Sadly, reliability is likely to be lower now that environmental legislation requires lead free solder in electronic equipment.

Luckily lead-free solder is not yet required in avionics, but I suppose that if you wanted to discourage the more cautious among us from traveling by aircraft, introducing this would work.