I've a small notebook computer than is small, light and perfect for carrying around in my backpack. The problem is the external PSU. Whilst it's tiny and rated with a 20v output @ 2A, 9 times out of 10 when I plug it in the 30A breaker in the house that protects the dedicated feed to the workshop trips.

I found an interesting article by Michael Allen of Bear Power Supplies that looks at the PSU inrush problem and some possible solutions.

You can download the PDF of the article below.

The village that I live in may as well be in the middle of the amazon in respect of getting a mobile phone signal. Actually, I bet you get a better signal in the amazon. The problem is my village is in a bit of a dip and the population density just isn't really high enough to warrant better coverage. We are lucky we get broadband (slow but it works) and electricity (it's on more than it's off these days which is nice).

In the UK at least, you can buy active GSM repeaters or signal boosters but they are illegal to use - who said the law was stupid. Several of the mobile networks also have their own devices that they sell but they require power and connection to your personal broadband.

In the good old days I would have just plonked an external aerial on the house and plugged my phone into that, but many modem phones don't have external aerial ports these days. So, what's the answer?

A wave guide!!

A wave guide is a simple arrangement of two aerials connected with a piece of coax. The idea is that that one aerial; usually a beam so it's highly directional and gives a bit of signal gain, located outside, as high as possible and pointing directly at the transmitter, is connected via a piece of the shortest and highest quality coax you can get your paws on to a small suitable indoor aerial. Signals are picked up by the outside aerial, travel down the coax and are re-broadcast by the indoor aerial. The trick is you don't want the aerials to close together that they interfere with each other and since you are not adding any amplification (as it's illegal and would mess up the GSM signal anyway), you need to keep cable runs as short as possible.

I'm really lucky in that a friend gave me most of the bits needed to assemble this wave guide including the outdoor beam aerial, the coax pre-terminated with N-type connectors and a suitable indoor aerial as well.

I decided to re-locate my communications aerial to the back of the workshop so it was as close as possible to where I spend the majority of my time.

The aerial above shows an extension pole, a wide-band communications aerial on the top (white stick), a black GSM aerial mounted on the side that is connected directly to a piece of kit in the workshop, and the main GSM beam aerial; aligned for vertical polarization.

The communications and black GSM aerials are working great.

However, I need to wait for my friend to come over next week with his spectrum analyser so we can align the main beam aerial. The aerial, but it's very nature is highly directional and because of the distance to the cellular base station, being out of alignment by a fraction of a degree will seriously degrade the set-ups performance.

We will plug in the analyser and very slowly scan the aerial left and right till we see a peek on the analyser at the correct frequency for O2 then lock down all the bolts.

What could possibly go wrong.

Once it's all up and aligned I'll report back on it's performance.

I've been really busy and Electronics time has been a bit limited, that said, I'm always eager to undertake projects that assist my work colleagues in their day-to-day tasks.

The organisation I work for have a pretty large fleet of vehicles based at 70 odd locations around a city. The vehicles are fitted with computing and other electronic gadgetry and so when vehicles are not on the road they are “supposed” to be parked at their base and connected to a vehicle charger, which is basically a 12v battery charger with a long cable and connector attached.

During an impromptu conversation around the coffee machine, it came to light that many of these charger units probably don’t work for one reason or another and there is no way of quickly testing them. There have also been problems with some of the vehicle charging ports wired incorrectly or simply having blown fuses, and I made a throw-away type comment that why don’t they have a simple gizmo that connects between the charger and the vehicle and can test the charger output voltage and the polarities. I love that glazed look that proceeds the “wow… can you do that”. Of course I can… I’m an engineer. Luckily, the fleet guy happened to have a charger drop cable handy with a connector fitted and from that I managed to find a suitable socket that would fit. So, using what I had available in the home workshop I designed and constructed a simple tester device prototype for them in an afternoon.

It had to be simple to use as the people using these aren’t really technically minded. It also had to be relatively cheap and strong as devices like this don’t tend to last long in busy workshops.

The pictures below show the case marked out for drilling, the underside of the assembled and mounted PCB, and the finished prototype device.

The drop cable from the charger plugs into the base of the unit, and the fly cable out of the tester plugs into the vehicle.

If either the vehicle or charger polarity is incorrect, the associated LED lights red. If both polarities are correct the charger voltage is displayed on the LEDs on the left; 13v or higher is “good enough”.

The operator can then press the “Load Test” button which simply connects the charger to the vehicle allowing the operator to see the on-charge voltage, and as long as it stays in the green, everything is ok.

If either polarity is incorrect; as indicated by the polarity LEDs, or either of the polarity LEDs don’t light at all; indicating no voltage present, an interlock disables the Load Test function. This is to prevent shorting the charger out if there is fault somewhere on the vehicle.

If readers are interested I’ll post the schematic and PCB foil but there’s nothing clever in this device. An LM3914 drives the 10 voltage output LEDs and the polarity indication is simply two red/green bi-colour LEDs. The only bit of any real interest was the interlock that prevents the Load Test button from working if there is a fault condition, but this is simple enough and makes use of a transistor and relay.

The one thing I was keen on was to reduce the amount of interconnect wiring to a minimum as whilst this was a fun little project and may have earned me some brownie-points with the management, it occurred to me they may ask me to create another 70 devices; one for each location, and that’s a lot of cases to drill and wiring to solder, hence my eagerness to reduce the amount of internal wiring to a minimum.

As often happens with prototypes, it was decided to change the voltage measurement scale to start from 11v and not 10v, which now means the Green band starts at 14v - thank heavens for trip-pots. You can see I drilled a little hole in the PCB so I can adjust it even when the PCB is mounted.

I was looking at designing a variable speed controller for the motor on my woodturning lathe. Nothing is ever simple.

Whilst doing some research I came across an article by Kevin Brady who explains in clear and digestible detail, all about Horsepower, watts and amps ratings of AC motors, and the complete pack of lies that some sales and marketing people try to dump on us when it comes to claims about how powerful the motors in their gizmos are.

It's well worth a read.

Happy New Year (to those that celebrate it).
As my first mini project of the year (and to give myself something to fiddle with over Christmas), I've released a small upgrade to the LED clock project I published last October.

By changing the PIC firmware and using this alternate display board, the clock can be turned into a basic Binary clock. Details can be found here.

The battery pack manufacturers are, in my humble opinion, scamming the general public into buying expensive battery packs when they don’t need to.

I’ve a Fujitsu Laptop that I use in spurts. Sometimes it’s in daily use being lugged around with me constantly, other times it gets left on the table under a pile of paperwork and not used for weeks at a time.

Recently I switched it on and the battery was flat and then found that it refused to charge. It’s around four years old so I thought that it had probably just come to the end of its life. The Laptop kept saying it was 98% charged but the charge indicator wasn’t illuminating.

I wondered if perhaps just one of the cells in the pack had failed (and the others could be useful for other things) but then I had a thought; I’ve seen this before with other so called “smart” battery packs. I took out my trusty Dremel power tool and carefully cut into the pack where I suspected the intelligent battery monitoring circuit was.

Once I’d cut into it, I could see the two connections going to the cells and placed a volt meter across them. The pack was reading 9.1v.  

I set by bench top PSU to 11v and hooked it directly across the terminals. I applied power for around 5 seconds, removed it, waited a few seconds and repeated a few times. After each cycle I would check the pack voltage and slowly it started to climb. Once I got the pack up to around 10v, I quickly inserted it back into the laptop and switching on the power. Hey presto, after a couple of seconds the charge indicator came on and Windows reported the pack was 4% charged… and charging. I left it charging whilst I got on with other activities keeping a fairly close eye on things (these retched batteries have a habit of catching fire) and after around 90 minutes or so, Windows reported the pack was fully charged and this was confirmed by switching off the mains power and the laptop happily running on its battery pack whilst reporting around 90 minutes of run time available. This is about right for this laptop.

Hindsight is a wonderful thing sometimes. Like may people, I've designed and built projects only to realise; usually when it's too late, that some slight changes or "tweaks" would have been of benefit to the project.

One of these projects is the breadboard PSU. A slight change to the PCB foil layout frees up some additional space on the breadboard. I've just updated the download file for this project with an additional PCB foil.

Another project that I'm in the process of updating is my recent LED clock. I realised after construction that there were a couple of unused I/O pins on the PIC that could be very useful if they were brought out to one of the connectors. There were some other design improvements that became obvious once I started looking at other things I could do with the project.

Of course, a lot of these types of issues are because as hobbyists we don't peer review our designs. At work, all hardware and software projects are looked over by somebody else on the team; a form of sanity check, and it's amazing how a fresh pair of eyes can spot obvious omissions and mistakes.

Now it's not often that I see a piece of tech that makes the hairs on the back of my neck stand on end, but when my friend Max Maxfield send me the link below, that's exactly what happened.

It's called Pixy, and I really really want one.

Read the full article and watch the demo video here:
http://www.eetimes.com/author.asp?section_id=36&doc_id=1319338

They have it connected to an Arduino but no reason why you can't drive this from a PIC, Raspberry or anything else for that matter.