alitalf: Skiing in the 3 Valleys, France, 2008 (Default)
I only recently found this report about a means to increase the capacity of lithium cells. It could be useful for many things. Netbooks and telephones are the obvious candidates, but it might also make electric cars genuinely practical.

If the use of renewable energy is to be substantially increased, will require a lot of energy storage, the doing of which is not currently known, if frequent power cuts are to be avoided, and this may be part of the solution.
alitalf: Skiing in the 3 Valleys, France, 2008 (Default)

It all works apart from the software!

 

I just need to program an Atmel ATtiny44 to measure a couple of analogue quantities and control a fast lithium battery charger, switching between off, trickle charge, and full charge, with detection of battery present, dead battery, and indication of being almost charged. There might be a use for a timeout in one section - or maybe not. Simples!

The charger even (optionally) adds negative incremental resistance to compensate for most of the resistance of the unreasonably thin battery cables. It can charge at 10A in a well controlled manner, and without getting unreasonably hot.

The software control I need is fairly simple - only a bit more complex than could have been done with something completely stateless (eg comparators and logic gates), but, in engineering of any sort, before a job can be done another must be done first, and that is indefinitely recursive. I need it finished by about mid Monday or trouble will result.

First of all I thought that the necessary software was already installed on my laptop, because I thought I had used it for something in living memory. No, the laptop failed and had everything I needed at the time re-installed, so I had to find out what things I need - which turns out to be AVR Studio and Winavr. I have an AVRISP 2 to program with which should be fine.

I have just reached the point of having upgraded its firmware to play nicely with the latest AVR Studio.

 

I do remember that there need to be some include files to make life easy, and I also remember needing to interpolate and extend the instructions in order to make that aspect of it work.

If When eventually I reach the stage that the header files are where the program expects to find them, so that the port addresses are defined and it is possible to address them by name, there will be some chance I can do the rest of it in a plausible number of hours. After all, the code needed should be simple enough that even someone out of practice like me, should be able to make it work. There is plenty of code memory, so it doesn't need to be optimised to the last instruction.

This is getting too close for comfort - I thought that both the computer and my memory were better prepared for this task. Maybe the missing bits will make sense tomorrow. As soon as I can even make the processor as much as toggle an output, I should be on the home straight.

alitalf: Skiing in the 3 Valleys, France, 2008 (Default)

I am learning to use KiCad with increasing speed, and it is certainly good to have a FOSS cad system that is available for Windows and Linux.

So far so good. However, the mapping of schematic to layout has problems.

Taking the example of a diode, the schematic (drawing) symbol looks like an arrow with a bar across the sharp end, with a connection at each end. One of the possible physical shapes for this can be SOT23, a shape used by several different components, including transistors, mosfets, and double diodes. The standard numbering of the three connections on a SOT23 goes, unsurprisingly, 1 2 3. A normal single diode connects to numbers 1 and 3, while 2 is unused.

Mapping the connections from the symbol to the physical shape requires that the pin numbers match, so if a diode is to use a standard SOT23 shape, its connections would have to be numbered 1 and 3. However, if the diode is to have another physical shape, then pin numbers 1 and 2 might be needed, or maybe even 2 and 3. A single schematic symbol would not work for this approach – but one of the intended strong points of KiCad is that one can concentrate on the schematic until that level of theoretical design is dealt with, and only then consider the detailed physical shape of the parts used. If a different (but similar looking) schematic symbol had to be used for different shaped parts, that level of simplicity doesn’t exist.

The alternative is to have separate layout shapes called, for example, SOT23-diode, SOT23-mosfet, and so on. If there is ever a need to change the dimensions slightly, for example to accommodate a change in soldering process, then all these separate footprints will need to be edited. Meanwhile, back at the diode, with a system like that, the diode connections would be labelled A for anode and K for cathode (don’t ask), and the diode footprint library would have pads labelled A and K.

Most electronics CAD systems have a third type of element, often called a device. That is a file that maps which connections on a schematic symbol match with which connections on the layout footprint, so that for any type of component there is just one schematic symbol, and for any layout footprint shape, there is only one of them regardless of how many different types of part use it.

I am still trying to decide whether there is a logical way to use KiCad, or whether it is (very reluctantly) necessary to purchase an upgrade to my existing EDWIN software in the foreseeable future. Edwin is good, but CAD software is usually very costly, so I am using a version from 1999 which will only work on Windows 7 using the virtual machine, and which I have so far failed to make work under WINE.

alitalf: Skiing in the 3 Valleys, France, 2008 (Default)
... 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 while LEDs, independently dimmable. The LED strip is made on a type of printed circuit consisting of a thick aluminium substrate, 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 us (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.
alitalf: Skiing in the 3 Valleys, France, 2008 (pic#91180)
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.

Read more... )
alitalf: Skiing in the 3 Valleys, France, 2008 (Default)
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.
alitalf: Skiing in the 3 Valleys, France, 2008 (Default)

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.

Read more... )

alitalf: Skiing in the 3 Valleys, France, 2008 (cat-1)
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.

ROHS woes

Jul. 23rd, 2008 04:10 pm
alitalf: Skiing in the 3 Valleys, France, 2008 (Default)

Since before the EU ROHS regulations came into force I have been wondering if the one that prohibits the use of lead in solder was a net benefit to the environment.

Yes, the solder in electronic equipment that is scrapped will be a bit less toxic, but:

1) It is all meant to be recycled anyway under regulations that came into force at around the same time (the WEEE regulations).

2) There will be more scrap because it will fail much sooner. 'Course, the councils will be able to charge us more to take the WEE to a recycling centre... and use more trucks and therefore fuel to do so.

I recently had an illustration of this when I tried to repair my niece's ipod. When I opened it I found that the problem appeared to be caused by a little of the solder paste not having melted, and having dried out and become a conductive dust in the works. The unused flux (I deduce) had caused corrosion when it got damp in the English weather, and so far repair has eluded me, despite repairing the obvious broken track and soldering the connections that were, previously, just touching.

With lead in the solder, there can (depending on the parts used) be tens of degrees between the temperature at which the solder melts, and the temperature that will rapidly destroy the components. Now, with lead-free solder, there is a wafer thin gap between not melting the solder and destroying everything rapidly by overheating. At best, some thermal damage is likely. At worst, a very few degrees of temperature difference between different areas being soldered can result in overheating in one place and not melting the solder elsewhere.

Today, while reading Electronics Weekly, I noticed this story about a lead-free reliability issue.

I think that the EU commissioners should be obliged to do all their air travel in aircraft with lead-free avionics for several years before anyone else does so. (There are currently temporary exemptions for avionics and military equipment.)

alitalf: Skiing in the 3 Valleys, France, 2008 (Default)
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; [livejournal.com profile] 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.

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