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Fibre to the premises – for Guinea Pigs.

Some weeks ago, the OpenReach engineer who came to instal our optical fibre decided that due to the thickness of a tall hedge on the boundary he would need a hoist (‘cherry-picker’) to reach the top of the telegraph pole, and one was not available that day.  He acknowledged that his work order mentioned this requirement.  Customer Services would be in touch to re-arrange the visit.

To cut a long story short, we arranged for them to come three weeks later (i.e. this week).  Again, they kept sending patronising messages about being here to let them in. ‘We’re ready, are you?’

An engineer from Kelly Telecoms turned up on time.  We’d done a massive clear-up job in an eaves cupboard and installed a power point for the optical modem, which we’d agreed with OpenReach as an ideal location.  He was a pleasant young man, but when we said ‘Where’s the cherry-picker?’ he looked taken aback.  “Oh!”, he said, “It’s still early, maybe I can get one!” Needless to say, he couldn’t.  “Customer services will call you!”

My partner was furious. “When will you come back? Should we leave all the stuff out of the cupboard or put it all back? If you can’t come tomorrow, we will have to put everything back into the cupboard, and then get it all out again.”

I decided to call customer services immediately.  After a 40 minute wait, I got through to someone who said that they’d have to transfer me.  After another wait, I got through to the fibre department who confirmed that four weeks earlier they had put a note on my order that they needed a cherry-picker! So, I wanted to know, can you come tomorrow?  “We’ll phone you tomorrow afternoon and make a new appointment.”

Needless to say, I have raised a complaint.  Due to the fact that both my partner and I work from home, we have to make prior arrangements if workmen are going to visit, and we are only available on certain days of the week. I’m beginning to wonder if I’m doing the right thing, especially as the Kelly engineer asked, “Why do you want full fibre? Do you have a problem with your present broadband?”  Rather like a doctor saying not to have an operation unless you’re really suffering.

I feel like a guinea-pig  – and we know how things turn out for them.

A built-in wardrobe project

The need for storage

We undertook a house extension project partly with the object of getting more storage, but this meant we lost our eaves cupboards, and for various reasons we ended with less storage for our hobbies!

This blog is a record of the process we have gone through to make a built-in wardrobe.  I’m a complete amateur and I’ve written this because I expect there are many other people who’d like to do something similar, and might like to learn from someone else’s experiences.

Carpentry skills

Because our free-standing wardrobes do not make good use of the space and are rather unattractive (you can see one to the right of the top photo), it seems sensible to install a custom-built wardrobe.  However, the last time I made any furniture was forty years ago, and my carpentry skills are those I learned at school sixty years ago (aargh!!) and from my father, whose early career was spent installing new-fangled electricity into people’s houses.  His tool bag contained a brace and several sizes of auger bits, some nice wooden-handled and bakelite-handled screwdrivers, and various insulated pliers and snips.  I also recall some chisels, hammers and saws; connectors and switches made of porcelain; and other odds and ends.  All museum pieces now.

Modern techniques

Watching our builders recently, I realised how much building materials and tools had advanced.  I’ve already mentioned buying a Bosch cordless drill/screwdriver, and I also bought a Bosch 18 v cordless circular saw.  These have proved to be wise purchases, and I have used them endlessly, especially installing some system-built bookcases and cupboards.  If you don’t have these in your toolkit, I’d say you should get them.

But how to build in a wardrobe?  I need to get it done as quickly and cheaply as possible, so I’d like to use standard parts for the doors and drawers – this means keeping to the modular sizes used for kitchens, i.e. generally in multiples of 100 mm.

The top photo shows the area where I’m installing it.  Will I be able to fit a modular system whilst not wasting space?


I’d already decided after measuring other wardrobes that it should be 600 mm deep (a suit on a coat hanger can be 500 mm wide, so a wardrobe doesn’t want to be less than 550 mm deep and there was no need to skimp on this occasion.  It was going to be full floor to ceiling in height.  I’d already decided that I want drawers at the bottom for shoes and similar items, and storage cupboards at the top for bed-linen, suitcases, sun-hats and the like.  Also some internal drawers for small items.

The base frame

I had great difficulty in getting accurate measurements.  Every time I re-measured, I had a different result.   I realised that the ceiling and floors sag, so they are lower in the centre of the room than at the edges, and the corners are not square.  I imagine this is a common problem.  In fact the floor has been hacked about by plumbers and electricians and has not been carefully reinstated, and there is an area where the fireplace was removed, so the boards are uneven.

I realised that for success, I needed a level base frame with square corners, in order to give me a reliable reference for the measurements.  I didn’t want to notch the framework to fit around the skirtings, so the first thing was to pull these off. I was glad that I did, because I could see there was quite a bit of wiring, some of which unexpectedly went up a corner of the wall, as can be seen in the photo.  But I also saw that the dab-and-dot plasterboard  had not been neatly finished behind the skirting at floor level.  Luckily, this area will be behind the drawers so I’m not going to repair this.

Basic structure

I decided that I would build the wardrobe with a standard “2 by 2” timber frame.  Nowadays, the equivalent is 44 mm finished planed square deal (pine softwood).  You will note that I have had to work in millimetres.  There is a terrible risk of mistakes if you mix centimetres and millimetres, and fractions of a centimetre are inconvenient.  Working by hand, I can’t get anything to a better accuracy than a millimetre.  (Previously, I’d always done my carpentry in inches, and although I’ve always worked professionally in metric units, this particular transition has caused me great angst.)

I decided that the structural house wall would form the back and one side of the wardrobe and that the other end and internal panels would be 10 mm plywood.  I could have used mdf but it’s heavy, not very good structurally, and I have a prejudice against it.

Modular system sizes

After studying various kitchen modular systems, I realised that the general assumption is that cupboard side panels are 15 mm thick, so that two adjacent ones are 30 mm thick.  This means that when you have a 1000 mm wide cabinet, the actual opening is 970 mm.  This rule applies whatever the nominal width of the cabinet.  Thus a 600 mm wide cabinet has an opening of 570 mm.  The corresponding 600 mm door is 595 mm wide.  This lets the door overlap the frame by 12.5 mm at all edges, with a 2.5 mm gap around the door and the outer edge of the cabinet.  This gives clearance around the doors whilst allowing slight sizing errors to be compensated by adjusting the hinges.

When two cabinets are fitted side by side, the dividing wall is effectively 30 mm thick. (I believe that “quality” cabinets may have 18 mm walls, i.e. two side by side are 36 mm thick, but this seems less usual.)  I’m not giving these details merely for interest: I found them to be essential for working out how to size the frame and the modules, as I will explain.

In my case, the deal framework thickness is 44 mm.  Thus two 600 mm units side by side would have two openings of 570 mm, but three frames each of 44 mm, so the width of the unit is 2 x 570 + 3 x 44 = 1272 mm, i.e. 72 mm wider than if made of a standard frame. This will create a wider gap between the doors. This doesn’t bother me.  I could have used thinner framing, but I wanted something sturdy, self-supporting and easy to work with.

Sketch of wardrobe
Sketch of wardrobe


Final dimensions

I spent a long time working out the layout to fit the space with standard modular sizes and provide the storage I wanted.  In essence, there are four bays, the one to the left is nominally 500 mm wide, the centre one is 1000 mm wide and the one to the right is 600 mm wide.

However, I really struggled with working out the position of the frame components until I realised how the modular system worked (as described above).

After several more measurements, I made a rectangular base frame with overall dimensions 2320 mm wide by 600 mm deep, using the 44 mm square timber, but I had to cut a notch half way along one end as the outer end of the stub wall had a steel corner bead that projected further out, reducing the width of the alcove at the corner by about 8 mm.  This won’t matter as I intend the plywood end panel to be inset by the width of a moulded timber bead.

Packing and levelling the base frame
Packing and levelling the base frame

I spent some time packing under the frame in the low areas and then screwed it to the floor, give a firm, level and square base on which to build.

Now how to construct the frame?  Unfortunately the ceiling joists run parallel to the frame, so unless there’s a lucky co-incidence, I will not be able to fix the top rail into the joists, so the frame needs to be self-supporting.  I considered various ways of joining the vertical and horizontal components (respectively called the stiles and rails).  For example, pocket screws, dowels, mortise and tenon, and cross-halving joints.  I need to be able to construct the frame in the back yard, take it apart and re-assemble it in the bedroom.  I decided that cross-halving joints were the best solution as I can make sure that the frame works before taking it inside and putting it back together, yet when glued and screwed, it will be very strong.

This proved to be a wise decision, as during the test assembly, I thought I’d made some horrendous measurement error until I realised that I’d mixed up some of the stiles and rails.  I made sure that I labelled them clearly to ensure that wouldn’t happen again.

I decided that the stiles would be at the front of the frame and the rails behind them.  However, I have made a bit of a blunder here, as the top rail will need to be chamfered to fit snugly against the sagging ceiling, and this means that the stiles need to be slightly shy of the ceiling, so it would have been better if the top rail is in front.  But I can use some beading as a cover strip, so this won’t be a big issue.

The next issue is how to support the frame during assembly.  I decided to fix the left-hand end stile first, as this can be screwed to the wall.

Left hand wall stile

My father always used those fibre Rawlplugs, but he had to use a hand tool for chiselling the fixing holes.  In essence, this had a hardened triangular shaped bit that you hammered into the wall, turning it a little each time.  Rather like the old miners used to ‘stope’ a blasting hole.  You couldn’t use an electric drill when there was no electricity in the building!  So I used them too and have always managed to get a really good fixing, which I rarely got with plastic plugs.  But walls are now made of composite, lightweight material and fibre plugs don’t give a secure fixing as the material is quite friable.


I’ve become quite a fan of Screwfix, as they have a warehouse within walking distance and always have a good stock of amazing things for professionals who aren’t going to stand any nonsense.  I decided to see what they had on offer for wall plugs and the choice was rather baffling.  They had a video demonstration of Fischer ‘Duopower’ wall plugs showing their adaptability and strength in many types of material, so I bought a box of the 30 mm long 6 mm diameter plugs.

So far, I have had excellent fixings in cinder block, brick and plasterboard. The cinder block is devilish, rather like aerated concrete (Thermalite), and turns to dust if you just look at it, so I’m impressed.

The next step was to fix the stile at the other end of the frame.  I realised that I could fit a support to the stub wall at ceiling level to do this.

Ceiling support at right-hand end

Now I was able to put in the right-hand post and after securing it to the this support, I could put in the other two posts.  The top rail could then be secured to the two outer posts and the middle posts could be put in and secured to the rail, to keep them stable.  The are glued and screwed for strength.

Frame self-supporting

The next stage was to fit the ceiling rail and the shelf supports. I’d already cut the notches for the ceiling rail into the top ends of the stiles.  Fortunately, all the stiles had fitted closely between the base frame and the ceiling, but I did have to chamfer the top edge of the ceiling rail so that it would fit below the ceiling.  This means the lower edge should be level so the top doors will fit square.

Next I fitted a 15 by 20 mm batten to the back of the shelf rail, 10 mm below the top of the rail and along the back wall, to take the top shelf, which is to be cut from a 10 mm plywood sheet.  It needed careful measurement of the batten height to make sure the shelf would be level.  I fixed it firmly with the Fischer Duopower wall plugs, which worked very well.  I fixed a similar batten along the inside edge of the base frame to take a base panel.  Although there will be drawers at the base, the structural floor is a mess and things do fall over the back of drawers, so it’s worth a bit of effort to avoid the possibility of things getting lost under the floorboards.

So, now onto cutting the shelves.  After carefully marking up a 10 mm plywood sheet, I cut these out using the Bosch Cordless circular saw.  Interestingly, this made the longitudinal cuts as if through butter, but it found cross-cuts a little harder.  Nevertheless it made a good job of them. I discovered that the base frame had gone slightly out of square when I fitted it, and I had to lose another 5 mm from the length in order to fit the base panel.

Next, I need to prepare the internal dividers, which will also support the hanging rails and drawers that I’m planning, so they’ll be carrying a lot of weight.  These will be from the same plywood, so will need to be firmly supported, especially as it is clear that it got damp and consequently bowed when at the timber merchant. I will use the 15 by 20 mm batten fixed both sides at the front and back, glued and screwed.  This will transfer the weight of the drawers and hanging rails to the stiles and the wall, and should be a very rigid structure.


Fibre to the premises

I’ve been so busy trying to get the renovated house ship-shape that I’ve neglected this blog.  But now to revert to an old hobby-horse, BT.

About 18 moths ago, I was writing about the impending demise of the aged hard-wired telephone system, the PSTN.  Epsom has a few ‘claims to fame’.  One is that it had the first automatic public exchange in the country, opened just over 100 years ago in 1912.  But its days are numbered.  Epsom been plagued for months by OpenReach vans laying optical fibre to enable ‘fibre to the premises’ service and indeed I got rather upset by ‘Kelly Communications’, who are contractors for OpenReach, festooning cables around and over my garden.

So I was rather expecting the call from BT offering me ‘Fibre to the premises’ giving 500 Mb/s download speed and a somewhat vague upload figure of 75 Mb/s.  The guaranteed speeds are not so impressive (250 Mb/s down and 10 Mb/s up), especially as I’d like a faster upload speeds for videos and so on. The price was £60  per month (£5 more than I’m paying for my present ‘fibre to the cabinet’ but in reality, I would pay slightly less as I’m dropping the ‘unlimited anytime calls’ option as we have made no outgoing calls on the landline for over a year!  Any calls we do make will now be ‘pay-as-you-go’ but as we both have unlimited mobile calling, we’d only use this in exceptional circumstances.

After agreeing to this, I felt rather bullied by all the ‘don’t forget your appointment’ messages:  ‘We are getting ready.  Are you?’

The guy turned up on time, and asked where the master socket was.  When I showed him, there was a look of dismay.  It turns out that they like to terminate the optical fibre on the inside of the house immediately at the point where it enters the premises and to put the optical modem there.  But my downlead wanders around the eaves for a considerable distance round several corners then disappears into the eaves and reappears in a room on the opposite side of the house.  This appears to be a legacy of alterations to the house and the GPO moving the telegraph pole several times during the ninety years since the house was built.  Not ideal as optical fibre isn’t easily jointed and the technician had only been supplied with a limited length.

The other issue is that the optical modem must be close to a power point.  (Some of the BT material talks about a battery backup unit, but he said that the Nokia unit they are fitting doesn’t have this, and there was little point since the router (home hub) needs mains power.)  I noted that BT has switched from Huawei to Nokia, but ironically the Nokia unit is proudly emblazoned ‘Made in China’!)

As it happens, the best and most convenient route is through an eaves cupboard to the ‘office’ where we want the router, but we have had to ask him to come back as we will have to clear a lot of junk from the cupboard, fit a power point and run a Cat 5 Ethernet cable to the office room.  The router can then be fitted in the office.

So what about the telephone service?  There is a socket on the ‘Home Hub’ for ‘Phone’ marked ‘For Digital Voice Customers Only’.  This looks like an ordinary phone socket, so presumably that is where the phone goes and hopefully it can supply enough current to ring my treasured extension bell!  This will mean the end of the power-failure-proof hard-wired phone, but we have been expecting this for some time now.

Annoyingly, clearing the cupboard is another job I have been avoiding, but I suppose it will compel me to get it done.


Scott Adams, the author of the Dilbert cartoons, must take credit for inventing this word.  He uses it to describe the way that marketing departments use deliberate confusion to get people to buy things that don’t do what they intended, or to pay too much for what they do want.

Robert Bosch Ltd

I have to nominate Robert Bosch Ltd in this category.  I’m embarking on some DIY projects – basically building a storage system in my new house extension.  I was going to get the builder to do this, but the Coronavirus lockdown has put all plans awry.  It has taken my builder much longer to complete the work as he was unable to get materials – and this was a genuine problem – and so other customers are pressing him and I decided I could build the storage myself as an interesting project.  However, I haven’t bought any power tools for over twenty years and I noticed that the builders had boxes full for every sort of work.  I decided that a cordless impact drill/ screwdriver and cordless circular saw could speed up the work.  (I’m often told that I take too long to do this sort of thing, but the builders have been very slow – maybe spinning work out during the lockdown.)

I looked around on the internet for buying advice and noted that Robert Bosch has a good 18 volt system with a large variety of DIY and gardening tools, so I could get more things as time goes on.

So then it is a matter of finding an offer at a good price.  This is where the confusopoly starts.  Firstly, their cordless drills come in different battery voltages – 12 v and 18 v.  Then they come in ‘Easy’, ‘Universal’ and ‘Advanced’ ranges. (There is also a separate ‘Professional’ range.)  Then the batteries come in three or four capacity ratings.  Then the tools come with or without batteries and accessories.

And of course, they are all different prices.  So it becomes extremely difficult to work out what you need and even whether you are buying what you intended.  You might choose the cordless combi drill with two batteries for £114 without realising that these are only 1.5 Ah batteries with a low-powered charger as this is only shown in the detailed specification – if you can find it.  And if you search on price, you can easily be confused as to what the battery capacity is, how many are included, what sort of charger you get and what sort of accessories.

So, I ended up with a drill/screwdriver with high-capacity batteries but without the impact function.  The price was fine, so I will keep it, as I have two mains-powered impact drills which will probably be better for some of the heavy-duty drilling.  This happened because whilst looking for the best price, I didn’t notice that they’d substituted an AdvancedDrill 18 for the AdvanceImpactDrill 18 that I’d been searching.

I feel I would have been wiser to buy a deWalt cordless combi drill with two 3.0 Ah batteries and rapid charger for £120.  It comes in a much more rugged case.  Indeed whilst de Walt offer a range, there does seem to be some sense in it, rather than too many options confusing options. Since my builder, who is a canny operator, is using these, there must be something to recommend them.

By the way, I partly criticise Amazon for this.  When you search for something, it comes up with a host of options and the distinction between the offers is often far from clear.

Wiring a new telephone master socket

Determining that the line is live

In the previous post, I explained that BT advised me to instal a new master socket myself.  My builder had installed a 4-pair cable (probably a standard CAT-5 network cable) from the BT drop-wire to my workroom (although I have no idea where the junction box is hidden), and had pushed the white/green pair into an old socket, so I guessed these carried the line. The CAT-5 network cable is not compliant with the UK telephone standard, but no matter.  A telephone line usually only requires a single pair nowadays, although my system originally had an earth connection from an earth rod near the drop wire, but this has long since been disconnected.   Earth wires were originally installed as part of a spark suppression system in the days of long overhead wires and in some cases were used as part of the exchange-calling system on so-called ‘party’ (i.e. shared) lines.

In the idle condition, the network pair carries a potential difference of 50 v DC, with the so-called A-leg being at 0 v and the B-leg at -50 v, relative to earth.  The polarity on the pair only matters in a few special cases, but I wanted to do the job properly, so I measured with a voltmeter to confirm that the line was active and determining that the white/green wire was 0 v (making it the A-leg) and the green wire was at -51.2 v (B-leg), see photo below.  This told me which wire to put into each of the terminals.

Testing the voltage on the A and B legs of the network ‘drop wire’

It is safe to touch the wires, although always wise to avoid this for the reasons I’ve previously mentioned.  However, if someone rings the line whilst you are touching them, you will get a nasty zing, because the ringing voltage is about 75 v AC at 18 Hz.  I believe that now it is around 100 v at possibly slightly higher frequency.  So the peak voltage is √2 times this, i.e. about 140 v, and the peak-to-peak is twice that, so plenty of juice to sting you.   Remember the electrician’s mantra – keep one hand in your pocket!

The NTE-5c Mk 4 master socket
Rear of base-plate with exchange wires connected. Non-standard wire colours – see text.

The NTE5c socket is a clever piece of design. It is in three parts – a standard-sized back-box that is fixed to the wall.  Then the base plate.  The drop wire is connected to a 1-pair cam-lock connector on the back of the base plate, marked A and B. Nothing else. The Base Plate is then fixed to the back-box by two screws.  This demarcates OpenReach’s ownership from the subscriber’s, who is not supposed to remove these screws.

On the front of the base plate is another cam lock connector, this time with three terminals, marked 2, 3 and 5.  They have kept the historical numbering, even though the other wires are no longer used.  Wires 2 and 5 carry the speech  and correspond to legs A and B, whilst wire 3 is the bell wire, and separates the AC ringing current from the DC loop current by means of a capacitor.  The Master Socket also used to have a surge protector across the A and B legs.  This was a small neon tube that would discharge a potential above a few hundred volts, preventing damage to the instrument or a shock to the subscriber, but the gas-filled tube also acts as rather a noisy capacitor at high frequency and thus makes the line noisy for the broadband signal, so it is no longer fitted.  It does mean that there is less surge protection than in the past, but this is much less of an issue than in the days of miles of uninsulated lines carried on overhead poles.  [I was once in a house during a violent thunderstorm when the fuses in the drop-wire junction box blew out.]

Connection of network wires to A and B legs of master socket

You don’t need any tools to connect the wires to the camlock connector. You lift up the clear plastic tab and then, observing polarity, push both wires through the front holes, then making sure to keep them straight,  through the back holes. It’s not quite so easy to keep them in place when fitting three wires – one can easily spring back.  If the wire isn’t through both holes, it may not be properly forced between the terminal prongs when you push the plastic tab back down. I would say this is a slight issue with the camlock connector.

Having connected the network wires into the rear of the back plate, secure it to the back-box with the screws provided.

You will see that there is a socket for a telephone plug on the front of the back plate.  Plug in a standard (non-powered) telephone.  You should get dial tone (you may need to wait a few moments) and be able to make (and receive) a test call.

So your line is working! Excellent.

Connecting the extension wires
Front of base-plate with extension wires connected

Returning to the NTE5c – you, the subscriber, can connect all your hard-wired extensions to the 3-way cam-lock connector on the front of the back-plate.  However, until the front plate is inserted, there is no connection between the exchange line and the subscriber’s wiring.  Instead, if you look carefully at the telephone socket in the back plate, you will see three wires at the bottom which are not connected when inserting an ordinary telephone socket, as these have no pins on the bottom edge. However,   when you plug in the front plate, this has a special plug that connects wires 2, 3 and 5  to the terminals on the front of the back plate, thus connecting your extension wiring to the exchange line.   The beauty of this is that when the front plate is removed, the exchange line is completely disconnected from the rest of the internal wiring, so if you can’t get dial tone from the socket in the back plate, the fault must lie of BT’s side of the system.

The front plate

As I understand it, two types of front plate are available.  One just has an ordinary telephone socket on the front, and the other has a telephone socket and a broadband socket with the necessary filters being built into the front plate, as in the illustration at the top of this post.

As mentioned, the front plate has a special plug that goes into the telephone socket in the back plate, but at the same time, connects the internal wiring circuit to the exchange side of the circuit.  The front plate is kept in place by two spring lugs and can be easily removed by the subscriber.  The idea is that if your line goes down, BT can ask you to remove the front plate (no tools needed) and ask you to plug the phone into the socket in the back plate.  If this works, they know the fault is on your side of the system.  They can then charge you whatever to come and fix it, or no doubt there will be independent firms who can investigate, perhaps more cheaply.

That really is a brilliant wheeze!

Fitting the extension bell wiring
The old-style GPO telephone extension bell with original wiring

The builder had run another 4-core pair to the position of the extension bell.  So I have re-fitted the bell and connected the blue and white-blue pair to terminals 2 and 5, and the orange wire to terminal 3 on the front of the back plate of the master socket.  The extension bell solenoid is connected at the other end to blue and orange wires.  The label in the bell-box states that as connected, the solenoid offers a resistance of 1000 Ohms, which is, I think, below the presently recommended value, but has always worked well.  Possibly it may not be so happy if there were more ‘ringers’ on the circuit.  Having now tested it, it is extremely loud, so there is plenty of current at the bell.

The ringing current

On a related subject, where does the ringing current and all the other system tones come from?  In the old Strowger exchanges, there was a ringing machine at the end of each rack, basically a motor-generator set.  The generator had a number of different windings to generate the necessary tones and a cam-operated set of contacts interrupted the tones to produce the brr-brr ringing cadence.  I can remember having an argument with someone who said to me ‘The phone is ringing at the other end’ and when I said ‘how do you know’, they said ‘I can hear it’.  They just could not understand that the ringing sound they could hear was supplied by the exchange, and was not the bell at the far end!

I hope this gives you a bit of insight into the telephone system and will allow you to instal your own master socket when necessary. Take care as always when working with electricity, especially at height.

BT amazes again!

Broadband connections

Some months ago, I had to switch to mobile broadband whilst I had some building work done. Unexpectedly, the builders had ripped out all my phone wiring!

So the builders have gone and I need my connection to be reinstated.  They got rid of everything, including the phone master socket, although they’d left the extension bell box in a corner because I specially asked.  Luckily the ‘drop wire’ from the network is still there.

Putting in a Master Socket

So I looked up how to put in a Master Socket.  This basically provides a termination to the exchange line and also separates the voice line from the broadband line (through a filter circuit).  Although it’s straightforward, a YouTube video I watched (clearly made a few years back) pointed out that it was illegal to fit a Master Socket yourself.  As I’ve said before, I worked as a student trainee for Post Office Telegraphs and Telephone (as it was then) and I remembered how ‘precious’ they were about it.  In those days, of course, they owned everything including the ‘instrument’ as the phone was called.  Telephones were permanently wired in and you couldn’t fit your own. Your instrument was rented and quite often your line was shared with a neighbour! They would say things like how an idiot householder could accidentally connect the phone line to the mains and this could electrocute a technician.

So I thought, well, I have a lot of things to do in the house, so I guess I will have to bite the bullet and get BT to do it.  Today I called BT and after a long wait got through to a nice girl in Blackburn. ‘Oh’, she said,  ‘Well we could do it for you but it will cost £130.  But you could just buy a socket in a hardware store and do it yourself.’.. ‘Right’, I said, ‘But I thought that was illegal.’  ‘Oh, no.  It’s perfectly fine and easy enough to do if the wiring is still there!’

I was gob-smacked.  So I’ve ordered a very nice ‘genuine Openreach’ NTE5C socket (which probably means Network Termination Equipment’ via Amazon and will look forward to seeing how I get on.  I haven’t yet tested the voltage on the line.  If I remember right, there should be 50 v across the exchange pair as long as the line is still connected.  From experience, you don’t feel this voltage, but it goes up to 75 v (AC) when ringing and this can give you quite a thrill.

I’m going to re-fit the original extension bell box as this is audible in the garden.  Should be fun.

Wait for the next instalment soon!

LED Driver Circuitry

Why choose an LED bulb

My previous post describes some of the considerations involved in using LED bulbs, with some detail on a G4 halogen replacement LED.   I got interested in this when searching online for some LEDs for a new light fitting I’d bought.  This was designed for six 20W 12v halogen bulbs. Reviews such as ‘It’s a pity this only takes 20W bulbs’ made me think that it probably wasn’t all that bright, even though it would use 120 watts.  Naturally, I thought I’d fit the brightest LED bulbs that I could get and after some time trawling the internet, it seemed that 6w bulbs were the highest power available in G4 fittings.  I ordered 10 cool white dimmable.

Needless to say, I’m wary of stuff from China – they always manage to find a way of exaggerating the specification, so when the bulbs arrived, I felt I should investigate a bit more.   This titchy bulb contains some quite sophisticated electronics.

The circuitry

In essence the base contains the circuitry on both sides of a flat board and the top part contains six small LED chips mounted on a rectangular glass substrate with yellow phosphor on both sides of the glass. It is all sealed in a soft, clear plastic resin, so care is needed not to bend it, otherwise the internals will be damaged.

The circuitry inside an LED lamp

Looking at the electronics board, on one side we have what is essentially the input circuitry – the big yellow rectangular blob is a smoothing capacitor and I assume that the rectangular things are  diodes for a bridge rectifier plus some resistors.  Together they create a nice smooth 12 v DC input from the 12 v AC that they are supplied with.  This is fed to the circuitry on the other side.

A 12 v replacement LED

Although I can’t read the designations on the small chip in the middle, it is something like the ZXLD1360 LED driver shown in the circuit diagram below.

Connections to the 1360 regulator chip

In essence, it is a current/voltage regulator that reduces the 12 volt input to that needed to drive the LEDs. Since each of the LED chips will need a forward voltage of around 3.4 volts and the supply is nominally 12 volts, I am rather assuming that the six chips are connected in parallel, as the connecting wires are too small for me to see.

Internal connections of the 1360 regulator chip
How does it work

This chip is in essence a current regulator.  The current to the chain of LEDS is sensed from the potential difference across a resistor (shown as Rs in the circuit diagram)  The circuitry in the chip pulses the main power transistor (MN in the circuit diagram) on and off at high frequency (kilohertz) to maintain the current at the design level.

The small choke L1  acts to smooth the current curve and also improve the power efficiency of the circuit. When the main transistor MN switches off, the magnetic field in the choke collapses  generating a reverse potential across the choke.  This feeds back to the input of the circuit through the  Schottky diode [don’t confuse the ‘S’ symbol on the cathode with the ‘Z’ symbol of a Zener diode: Schottky diodes have about half the forward voltage drop of an ordinary silicon diode] and thus light the LEDs on the reverse half-cycle.

Since there are six LEDs in the bulb, then each must consume 1 watt if it is a six watt lamp, If the lamps are in parallel, then with a voltage of 3.3 v across each one, the current must be 0.3 amps, requiring 1.8 amps for all six lamps.  But the circuit can only provide 1 amp.  I suppose they could be connected three in series (as shown in the circuit diagram) and both of the three in series being connected in parallel.  It is best if they are all connected in series, as this ensures that the same current flows through each, which evens up their brightness.  Sadly, I think it is more likely that they will claim that the ‘W’ doesn’t mean watts at all, but perhaps ‘way’ in other words it has six diodes in it.  I suspect the diodes are not likely to take more than about 100 mA each, if that, so it probably consumes 0.3 watts per diode and maybe 1.8 watts all told.  In other words, quite a lot less bright than the 20 w halogen.  I will measure this when I get access to the 12 v transformer.


Moreover, I’m pretty sure that this will not work with a dimmer – in fact it does its best to maintain the LED current whatever the input voltage, so will resist attempts to dim it.  The chip does actually have a separate dimmer input to it, but this needs an external connection, which obviously you don’t have in an ordinary lampholder.  However it is not impossible that this is connected to detect changes in the supply voltage and thereby regulate the brightness.

On this point, it is worth noting that you can’t adjust the brightness of an LED by altering the driver voltage.  The diode will only conduct (light up) when the input voltage reaches the internal voltage drop of the diode.  If you try to turn the voltage higher, the voltage will remain at the internal voltage drop, but the current will increase and the LED will be brighter.  But if you increase the current too much the LED will overheat and burn out.  The usual way of controlling the brightness is to pulse the LED on and off.  If this is done at a high frequency, the light will appear less bright and the flicker will not be perceived. If the pulse rate is too slow, the flicker can become perceptible and cause problems for many people.

So you live and learn.  to be honest, the bulbs were remarkably cheap, so I couldn’t have expected more and it is an interesting learning experience.

240v G4 LEDs

As a footnote, I bought some 240 v LEDs as well.  These just have a ‘capacitive dropper’ to regulate the input voltage and these probably would work with a dimmer.

Light Bulbs

In the old days, buying a light bulb was simple.
• How many Watts?
• Pearl or clear?

There were some special bulbs, such as for projectors and for photography, but these weren’t mainstream and you’d have to go to a specialist supplier to get one.

Bewildering choice

Nowadays, the choice is bewildering, and something I’m having to resolve as I’m refurbishing my house, so I thought it would be useful to summarise some of the considerations.

Incandescent bulbs were progressively phased out in the UK from 2009 to 2014, being initially replaced by ‘compact fluorescent’ or CFL bulbs and subsequently by LED bulbs.

‘Halogen’ incandescent lamps are still permitted but are generally only used where a small light source is needed, such as in projectors, car headlamps and for some decorative uses.  These are most efficient when operated at a low voltage (generally 12 volts) so these need a transformer in domestic use.

LEDs are the norm

It is fair to say that LEDs are now the norm.  They are bright, come on immediately, generate little heat and have a long life.  They are not perfect.  The main disadvantage is that they can give poor colour rendering.  So lets look at this.

Black body radiation
The CIE colour space and black-body colour temperatures

An incandescent bulb radiates light due to the high temperature of the filament.  The radiation [nothing to do with radioactivity]  is close to a ‘black body’ radiation, which is dependent on the temperature of the heated object – in this case the filament.  We are used to seeing things under such illumination, as this is approximately what we see under sunlight (ignoring the effect of atmospheric absorption).  A black body emits light in a continuous spectrum which peaks at a certain frequency (colour) according to its temperature.  The higher the temperature, the bluer the peak of its spectrum. The ‘Colour temperature’  of a lamp means the temperature of a ‘black body’ when heated sufficiently to glow at the same colour that the lamp gives out.  It is usually expressed in ‘degrees Kelvin’ which are 273 degrees more than degrees Celsius – in other words, water freezes at 273 degrees Kelvin.  0 degrees Kelvin is ‘absolute zero’, where an object has no thermal energy.

Colour Temperature

On the colour temperature scale, a bright red glow is 1000 degrees Kelvin.  At 2000 degrees Kelvin, there is a bight orange glow, rising to a bright yellow glow at 3000 degrees, a yellow-white glow at 4000, an almost white glow at 5000 and a pure white glow at 6000.  At 7000, glow is a blue-white and at 8000 it is distinctly blue.  By 10000, we are looking at a bright sky-blue colour.  The colour temperature of a typical incandescent or halogen bulb is about 3200 Kelvin.

How LEDs work

However, LEDs don’t work by heating an object.  They work by ‘exciting’ electrons to vibrate within atoms, which when they fall back to their rest state emit a photon, depending on the material they are made from.  Nowadays, most LEDs emit photons in the blue or near ultraviolet range, but the blue/UV light is absorbed by a phosphor coating that emits visible light in the yellow range of frequencies (which is why the surface of the LED looks yellow when not illuminated).  By adjusting the balance between the blue of the LED and the yellow of the phosphor, the light can look white (often ‘warm white’, or ‘cool white’  but in reality it omits large parts of the spectrum, especially in the red.  This can mean that the colour rendering of LEDs can be very poor, particularly for skin and other surfaces containing a lot of red.  For this reason, lamps are now given a ‘colour rendering index’ (CRI) which indicates how closely the lamp reveals the colours of an object compared with a natural light source.  A CRI of 100 means that the lamp shows colours exactly as they appear under ‘standard’ daylight.  The test is done by looking at special test colour samples under the lamp and under light of the reference ‘colour temperature’ and rating the differences observed.

Colour rendering
Spectrum of different lights

Typical ‘white’ LEDs have a CRI around 83,  which is better than old fluorescent tubes, but far from ideal,  so this information is often omitted in marketing details.  However a CRI above 90 is needed for good colour reproduction.  It is possible to get better colour rendering by using phosphors that emit red, green and blue light.

A warm white LED has a colour temperature of 2700 K, which is considerably more yellow than an incandescent bulb.

A particular difficulty can exist for film and video lighting, because the spectrum of the LED, even with a high CRI, may not match that expected by the colour sensors in the camera.  For this reason, a special colour rendering index has been developed for video use.

Luminous efficiency

In the old days, you knew how bright a 100 w or a 60 w bulb would be.  LEDs need far less power but the amount of light they give out (which is measured in lumens) depends on their design.

The two-colour white LEDs have the best efficiency, around 120 lm/W whilst 3-colour LEDS produce around 70 lm/W, although the amount of power they need also depends on the efficiency of their control circuitry.

By comparison, an incandescent lamp produces about 15 lm/W and a CFL produces 63 lm/W.

This means that to a rough approximation

Incandescent  LED     Lumens
100 W                24 W        1800
75W                    15 W        1000
60W                    11 W           900
40 W                      6 W           400
20 W                      3 W           300

The circuitry inside an LED lamp

There is yet another consideration – can they be dimmed?  This is not primarily anything to do with the light-emitting diode, but the electronic circuitry within the lamp.  All domestic LEDs have control electronics in the base of the lamp, because the LED must be fed with direct current at 2 to 3 volts.  There are a variety of ways of reducing the mains voltage of 240 volts to this low value, but usually by ‘chopping’ the incoming AC mains so that it is only on for part of the cycle.  The chopped mains ‘fills’ a capacitor until it reaches a certain a low voltage, and then stops the current, which then discharges into the LED.  Depending on how this is done, the lamp may not work with a dimmer, which also chops the mains voltage to drive less power into the lamp.  Some lamps can be dimmed, but only with a ‘trailing edge’ dimmer.

The lamp cap/base

There is yet another consideration – the lamp base.  Traditionally, only the ‘bayonet’ cap was used in the UK, but with the influence of Europe, ‘Edison Screw’ fittings have become very common. Both these ‘caps’ are available in different sizes.  It is not part of this article to consider the pros and cons of the two types of fitting. Most of the lamps described above are available in these two ‘caps’.

Bi-pin caps

There are also many types of ‘bi-pin’ fittings which originated for different purposes. G4 is a small bi-pin fitting originally designed for low-voltage halogen lamps.  G9 is a slightly larger fitting used with higher-power bi-pin mains voltage lamps, and G10 is a large bi-pin fitting intended for high-power mains halogen lamps.  However, these have all be re-purposed so care must be taken that your lamp is for the correct voltage as well as the correct cap.

Considerations when choosing

So, when choosing and LED bulb, the main considerations are:

  • the cap/base to fit the lampholder
  • the voltage of the bulb 230/240 volts in the UK, but may be 12 v in fittings with a transformer to replace some halogen bulbs
  • The colour temperature
    • 2700 = warm white, (i.e. yellow)
    • 4000 = natural white (i.e. sunlight)
    • 6000 = cool white (i.e. skylight)
  • Dimmable or not
  • Colour rendering (if you are doing art/design work)
  • Lumens output
The Circuitry

For those interested in the technology, this titchy bulb contains some quite sophisticated electronics.  I have decided to cover this in a separate blog called LEDs – The circuitry

On one side we have what is essentially the input circuitry – the big yellow rectangular blob is a smoothing capacitor and I assume that the small rectangular things form a bridge rectifier.  Together they create a nice smooth 12 v DC input from the 12 v AC that they are supplied with.  This is fed to the circuitry on the other side.  Although I can’t read the designations on the small chip in the middle, it is something like the one shown in the circuit diagram below.  In essence, it is a current/voltage regulator that reduces the 12 volt input to that needed to drive the LEDs.  I am rather inclined to think that this will not work with a dimmer – in fact it does its best to maintain the LED current whatever the input voltage.


More on scams

A small token of appreciation from the Windows team
A clever scam

I got an email from the address ‘engage dot windows dot com’ offering me some nice screensaver photos and various other ‘useful’ links.  This is the first time I’ve ever had anything like this, and knowing that images can contain hidden pixels that try to instal malicious code, I was highly suspicious.  Oddly, I had just updated my screensaver photo with one of my own that I particularly liked, so I wasn’t interested in theirs.  I have Googled the link and whilst I haven’t had a ‘red alert’, I think this is a very clever scam.

Probably not a scam

I had reason to make a small insurance claim just before Christmas. Yesterday I got a phone call purporting to be from my insurance company regarding ‘my recent claim’.  Almost everyone has had such a call – usually a random attempt at ‘ambulance chasing’ – they hope to get a reimbursement of their expenses when they find a susceptible person.

I’d already confirmed some of my details when an alarm bell rang – they were calling me on my mobile number but had not even attempted to confirm their bona fides.  I said to them, ‘Hang on, what is the claim number you are calling about?’  ‘We can’t tell you that , Sir, it’s data protection, you know.’  Then they said, ‘You gave us a “memorable word”.  Can you tell us what it is?’  Well, I couldn’t remember it off the top of my head, and I asked them to call me back in ten minutes.  Her reply was ‘Don’t worry, Sir, we’ll send you a letter.’

The more I think about it, the more this smells.  They had phoned me on my mobile number and asked me for personal details but had told me absolutely nothing.  Luckily I had given them nothing that wasn’t in the public domain, but it would have been so easy to let something slip.

If they were genuine, it would have been easy for them to say that it was about a claim submitted on a certain date and give me part of the claim reference number, or part of the memorable word, before asking me for personal information.  Was it, or was it not a scam?  Even if I do get a letter (and so far I haven’t), I will never be sure.

Update on Hardware & Software for making demo videos

I said I would update my previous post when I’d made a couple of videos.  Well, I have made four short videos, so here is a follow-up.

I have found OBS studio to be fantastic! I hardly need to say more.  It’s true that it doesn’t come with instructions, but there is plenty of help available on the web and anyone with some familiarity with Windows will soon find the best way of using it.  I set up OBS studio to record mp4 videos as these are quick to edit and easy to upload to YouTube.

I don’t pre-script my videos, although I do think about what I want to show and how I’m going to present the demo – I do a lot of live demos.  However, I’m often a bit hesitant in my speech, having to think how to do something whilst talking about it.  So I cut out the mistakes and dead space using Adobe Premiere Elements, which is very quick with mp4 videos.  I also shorten them all to about 12 minutes, which is probably enough for anyone to absorb in one sitting.

Regarding the microphone, I have decided that I like the £24 KLIM better than the £85 Blue Yeti.  Whilst the Blue Yeti probably has a better frequency response, the KLIM has a power on-off switch which means I can leave it plugged into the computer.  Also it is better at rejecting the fan noise of the computer (I use a powerful tower machine as I do a lot of CAD work and because my present work space is cramped, I can’t escape from the fan noise). It doesn’t pick up too many breathing sounds or desk bumps. And it is smaller and lighter, again important on my cramped desk.  I think the sound is excellent – I don’t have to be too close and I think my voice sounds quite good.

I can recommend this as an excellent and productive combination that will encourage me to make more demo videos.