Category Archives: Bits and pieces

Retrofitting a Bosco IXO cordless screwdriver with a USB-C charger connector

In this age of USB-C – I’m beginning to tire of things which require Micro USB to charge.

Today’s annoyance: My Bosch IXO. At the time of writing neither my model or the current one charge with USB-C. No doubt people at Bosch are beginning to ask “Do we need to take this new USB seriously?” – but that doesn’t help us much right now.

So let’s open it up.

Damnit. It’s all on one PCB, and there’s a nasty piece of rock hard epoxy behind the micro USB connector. This rules out making a ‘Retrofit’ PCB – which would have been a cool project.

After a good blasting with my Leister Hot Jet S – the old connector and the epoxy is gone. Small bummer that I tore those unused pads from where the connector was, but we don’t need those anymore. I’ve also got a couple of wires there to lead to the new connector

Now – what are we gonna put in its place?

I bought a few Micro-USB to USB-C adapters off eBay and tore the plastic case off one of them. They are compact and have everything we need.

We now have the new connector soldered down. This was quite tricky. I found that the easiest way was to position it by tying it down with some copper wire before soldering. The shell of the USB-C connector is soldered down to the ground pad on the PCB previously used by the Micro USB connector.

Wiring is simple. With those red/black wires I previously soldered on connected to the Micro USB GND/VBus connections. The required 5.1K resistor is already on the adapter PCB.

For added strength that copper wire also goes through the PCB.

You can also see a tiny piece of Kapton tape under the connector. This was to stop the shield of the USB-C connector from shorting the pads used by the old micro-USB connector. By not outright removing all of those pads I made life rather difficult for myself – too late now.

And finally some new epoxy to ensure we’ve got a nice strong bond to the PCB.

Last job is to grab some needle files to increase the aperture in the case to the new larger size needed by the USB-C connector.

In the end it turns out we have something a lot tougher than the original arrangement, because of the longer length of the USB-C connector it now protrudes from the case meaning we can make a nice snug fit for it, significantly lowering the chances of damage by yanking of the charging cable.

That extra length of the connector also means we don’t have the annoying problem of plugs which aren’t the same shape as the supplied charger not fitting in either.


Unfortunately this doesn’t get our IXO all the way into the world of USB-C. PD aware “true” USB-C chargers like for example the Apple 18W iPhone charger, or USB-C Macbook chargers refuse to charge it.

To get full USB-C compatibility we would need an extra chip to negotiate the charge voltage. There are quite a few of these on the market now but we would have to make a custom PCB due to space limitations in the IXO. This is good enough for me – anything which has a USB-A connector on it will work just fine.

This all took me about 2 hours. Not an easy mod unfortunately. But if you have the skill and patience – well worth attempting.

Fixing a Sony KDL-40W5810 with a “14 blink” error code

My dinosaur TV back in action after repair – reassuring to see that little has changed in the world since it last powered on

A little while back I bought this TV cheaply off Gumtree – probably one of the dumber things I’ve done, as it had an array of small but annoying problems, but recently it upped the game and failed to turn on, giving the above described blink code (which shows as 13 blinks, then followed by 14 blinks continuously).

Frustratingly there doesn’t appear to be any official triage documentation for this model online. A bit of googling around offers a few possible causes ranging from mainboard failure, LCD panel failure (?) and TCON (timing controller) failure.

But which is it? I first checked all the voltages on the power supply, all good, looked briefly at the TCON, couldn’t see any obvious issues there. I also took a look at the backlight – the mainboard wasn’t even attempting to power it on, so not likely the issue, but just to be double sure I powered it up manually by applying +3.3V to the BACKLIGHT_ON signal on the power supply. Sure enough it came on and none of the error signals were asserted.

Now I know the problem is either the mainboard or the TCON. I took a stab replacing the mainboard – hitting up eBay for a cheap second hand part. Upon installing it, I now get an 8 blink error code? More googling reveals an issue with the audio amplifier.

Ah. I see, so someone has torn the connector from the PCB when removing it from the donor TV. We can see those small traces have been torn the pads the connector was soldered to.

This was causing the 8 blink error code, as those small traces lead to an ADC which tests for DC offsets from the audio amplifier. This check ensures that we don’t end up with smoke pouring out of the speakers in the case of a blown transistor in the audio amplifier. In this case there was no DC offset, the error was just the ADC inputs drifting all over the place because they weren’t connected to anything.

JST PH header bodged in place of the missing original header

Above you can see I’ve dickied a JST PH connector in place of the missing original – not quite the same as what was there but close enough, also taking care to reconnect those small traces. The original harness mates with it OK – just doesn’t latch.

So I switched it back on with the new mainboard… 8 blink error is gone, and now we’re back to 14 blinks. FFS. The good news is that the eBay seller fully refunded me when I complained of the damage, and I’ve still got the replacement mainboard, but, my TV still ain’t workin’.

So, let’s look at that TCON then.

The TCON is under the aluminum shield circled in red. It converts the serialised picture data from the mainboard to the parallel signals required to drive the LCD panel.

I had purposely not gone down the path of replacing this because it’s not an easy part to find and I had read on other sites that if you disconnect the LVDS cable (the large black one which interlinks it to the mainboard), then power on the TV and it remains powered on (without a picture), then you definitely know that the TCON is at fault.

This was not I observed. In my case I get the 14 blink code regardless of whether or not the LVDS cable was connected. Additionally I had also spent a bit of time checking all of the supply voltages on the board, everything looked OK, hence attempting the mainboard first.

It turns out that bit of advice was rubbish in the case of my TV, because the 14 blink error code is seen both in the case of a TCON which fails self test, and when the TCON is disconnected.

I know this, because I found another (brand new) TCON very cheaply at a local TV service company, mis-labeled as “for Samsung” – knowing this is a rare and pricey part, I wasn’t going to be asking any questions. Upon installing it, my TV is now working again.

The old TCON PCB

I’m picking that few faulty TCONs can easily be repaired, because this board subject to more thermal stress than anything else in the whole unit. After years of thermal cycling it’s likely that this one has died as a result of cracked BGA solder joints.

If you are keen to repair a TCON with this kind of fault – a good starting point would be to re-flow or re-ball, perhaps even replace the gamma processor and its memory (the three BGA chips on the left). The TCON itself (silver topped chip in the centre) is less likely to be an issue due to cooler running temperature.


Success in the end, with a lot of time spent on a worthless item. Perhaps a small bonus that the largely needlessly replaced mainboard fixed a couple of other minor faults. I’d have been a lot more successful if I’d never bought the damn thing in the first place.

Does the Dell Latitude M.2 WWAN socket have the SATA interface on it?

Recently while trying to answer this myself, I found a lot of discussion on this subject, but no definitive answer.

M.2 B Key sockets have a variety of possible modes as defined by the NGFF specification:

The second to last mode “RFU” (Reserved for future use) is defined by Dell as:

I am unsure what HCA stands for, but have seen it printed on the silkscreen of some of my earlier latitude models. Clearly it is some kind of proprietary device that requires one PCIe lane. It may stand for Host Channel Adapter – Implying some kind of non-NVMe PCIe SSD (i.e. has an Option ROM).

None of this tell us anything about what Dell have actually implemented on thier WWAN slots, neither does their tech support, or any of their documentation. I found myself eyeballing the traces extending from the socket, but even this was inconclusive as a lot of them are fed up from vias under the socket.

It’s given that it’ll have SSIC/USB 2.0 because almost all WWAN cards use those interfaces, but what of the others?

Fortunately there’s no need for any further conjecture because the schematics for these models are floating around the internet, so let’s answer that question definitely.

The above diagram covers models 7280, 7380, 7480, 7490 and likely others too. So there we have it. The interfaces on the WWAN socket are:

  • USB 2.0
  • SSIC (Chip-to-Chip USB 3.0)
  • PCIe (Permanently disabled in BIOS)



Just because we know what interfaces are there, we still don’t know what kind of peripherals will actually work. For example – if a socket can accept WWAN-PCIe – SSD-PCIe should also be no problem as the required connections are all there, however those devices will have their configuration pins tied differently, allowing the BIOS to determine exactly what’s attached.

This allows manufacturers (for example) to allow PCIe WWAN cards, but disallow PCIe SSDs. On top of that, just because an interface is there, it doesn’t mean that it’s actually enabled.

This turns out this is the case for my Dell Latitude. While the PCIe is there, it cannot be used because the port on the root complex is disabled in the BIOS, and there’s no way to enable it (without hacking the BIOS). I was able to confirm this by testing out a variety of B-Key PCIe devices, none of which were detected (even when strapped as WWAN-PCIe).

A dick move by dell, but given how rare WWAN cards requiring PCIe are, they had no reason to enable it, and my experience from owning previous models is that they’re pretty good at tying up loose ends like this.

Short of hacking the BIOS, or building a new type of USB 3.0 card from scratch, only WWAN cards will work in the WWAN slot.

Yours may differ

Older Dell models did have SATA+PCIe in the WWAN socket, but this is not the case for more recent units. The story will inevitably be different for other manufacturers.

Those Thunderbolt to PCIe boards which shouldn’t exist, but do

If like me you happen to have a Thunderbolt 3 enabled laptop, and are finding yourself wanting to attach arbitrary PCIe peripherals to it, you may have found yourself looking for some kind of adapter board.

You may also be aware that such items are strictly forbidden under the Intel Thunderbolt licensing programme. This is because thunderbolt chips are only sold for use on certified products. As a device like this is only part of a product, it could never be certified.

But that doesn’t technically stop it from existing. In theory this problem should go away with the upcoming release of USB4, but that may be some time away.

You may have seen one of these on either eBay or AliExpress:

AR SP BPD PCIe_Rev_2p1

But what is it? How can it exist? It appears to have the same dark green hue and silk-screen font as an Intel reference board (of which I’ve got quite few). I’d be comfortable to say they did indeed make this.

Quite how they’ve ended up for sale is an interesting question. What’s even more interesting was the transaction its self. I bought this off AliExpress, paid in U.S. Dollar, apparently ship from China in 20 days… but…

It arrived the next day! Shipped from the Amazon UK warehouse?!

Yup. This thing came from the Amazon UK warehouse. What the hell!

This certainly adds the the intrigue of who exactly it is that is selling them, not to mention how. The punchy price tag tells us they haven’t got an unlimited supply of them.

Sellers generally advertise them as for SSD use only. This is more because it only supplies 3.3V to the attached peripheral than anything else. Most PCIe cards also require 12V which this board does not supply. That doesn’t stop us from providing the 12V separately.

Plugging it in

The thunderbolt info dialog describes it as an “LT-LINK Node Lite” – a similar name to the AKiTiO Node Lite. We also see the warning there about a graphics device which “may not function properly” telling us that the firmware on this board was for some kind of eGPU enclosure.

Using it

To test it out I’ve decided to throw a rather curly scenario at it –

I’ll be attaching it to my ExSys PCI chassis. Fitted will be an Intel PRO/100B – a 24 year old conventional PCI adapter, which doesn’t support 64-bit DMA (nor does it have 64-bit drivers). Fortunately the source code for its driver is in the Windows DDK, so I’ve compiled it for 64-bit Windows for this test…

This test will also add another couple of PCI-to-PCI bridges onto the existing arrangement in the Thunderbolt chain.

The chassis is connected to the Thunderbolt adapter via the PCIe card option.

Yeeeha! Got PCI-to-PCI bridges? I quite frankly have no idea which of those is where, or doing what.

Even with a long chain of bridges,  a transition to conventional PCI, and the rather legacy nature of what I’ve attached – it works, and passes traffic.

So there we have it. You can indeed use peripherals other than SSDs on these!

Silencing a Cisco 2951 (for where ever silence may be required)

A little while back I wrote a post on silencing a Cisco 2911 for home use. You can read about that here. I accept that it’s unlikely anyone would be using 2951 at home however you may find yourself in a situation where you need to reduce the noise level of this router. In my 2911 guide I went to the extent of rebuilding the power supply as a 12V DC version to reduce heat output. We’re not going to be bothering with that here, instead we’ll be looking solely at the fans. The first task is to remove the four original fans. Remove all the screws you can see on the fan module, and release the plastic clips holding the face plate.

Extracting the contacts from the mating connector

Next step is to unpick the contacts from the receptacle I personally used the Molex Mini-Fit Jr extraction tool (11-03-0044) – which is the correct tool for this, however you may find it more convenient to just cut the wires off the old fans and splice them onto the new fans.

Stock 2951 fans removed

In my case I’ve used the same gold-plated Mini-Fit Jr contacts (42815-0012) as were used on the original fans. You may not feel the need to bother with those. You can read more about these connectors here. Just in case it isn’t obvious – the pinout for that connector is as follows:

  • 1 : GND (Fans 4, 3)
  • 2 : +12V (Fans 4, 3)
  • 3 : PWM 3
  • 4 : TACH 3
  • 5 : +12V (Fans 1, 2)
  • 6 : GND (Fans 1, 2)
  • 7 : Module presence strap
  • 8 : PWM 4
  • 9 : TACH 4
  • 10 : PWM 2
  • 11 : TACH 2
  • 12 : PWM 1
  • 13 : TACH 1
  • 14 : Module presence strap

The next step is to re-install connections for fans 1 and 2 only, as we’re going to blanking up the holes for fans 3 and 4. If you’re not replacing the contacts entirely like me, you won’t need to be bothering with this.

Connector from bottom
Connector from top

As previously mentioned, connections for fans 3 and 4 are omitted, except we’ve strapped the tach signal from fans 1 and 2 to them to keep the software satisfied that all 4 are present. Now we have to assemble the new fan module. I’ve used two Delta AFB0612VHC fans. I don’t personally see the need to go splashing out on expensive “ultra silent” fans from the PC modding scene. You can if you like but they’re not going be much (if any) quieter than these.

The fan module with only two fans installed. It is important that these positions have fans fitted as this is the side with the power supply and CPU.

I have also blanked up the holes for fans 3 and 4, to ensure airflow remains consistent. Next step is to re-assemble the fan module, and plug it back into the router – making darn sure you’ve wired it properly first. Now, the obligatory ‘show env’ to check that everything’s OK:

Router>show env
 Internal Power Supply  Type: AC
 Internal Power Supply  12V Output Status: Normal

 External Redundant Power Supply is absent or powered off

 Fan 1 OK, Low speed setting
 Fan 2 OK, Low speed setting
 Fan 3 OK, Low speed setting
 Fan 4 OK, Low speed setting

 Intake Left temperature: 21 Celsius, Normal
 Intake Right temperature: 20 Celsius, Normal
 Exhaust Left temperature: 34 Celsius, Normal
 Exhaust Right temperature: 25 Celsius, Normal
 CPU temperature: 59 Celsius, Normal
 Power Supply Unit temperature: 49 Celsius, Normal

 Battery OK (checked at power up)

 Motherboard Components Power consumption = 55.3 W
 Total System Power consumption is: 55.3 W

 Environmental information last updated 00:00:04 ago


Looks good.

Caveat Emptor

As I stated in my previous 2911 guide, when we make modifications like this, we’ve got to consider the consequences. For the 2951 you’ll not be able to use it with any service modules. If you need to install service modules, I would recommend using 4 of these fans.

How much quieter is it?

To save you from asking – it now makes about as much noise as a middle of the range ATX power supply under a favourable conditions (i.e. small load, and room temp of 20 degrees Celsius.

AMP RJ45 vs WE/SS (Regular) RJ45 Plugs

We’ve all heard that they’re different (somehow?) I thought this was going to be straight forward, turns out I was wrong.

Before we get into the details, we need to define what exactly an “AMP” plug is. In the first instance an AMP connector is made not by AMP, but CommScope. The AMP company was dissolved many years ago and its products have gone through various rounds of divestment and acquisition. Other brands this type of connector has been sold under (historically) are “Tyco” and “TE Connectivity”.

Non-AMP plugs are generally referred to as Stewart Stamping (SS) or Western Electric (WE) Style.

The second thing to consider is that eBay is awash with counterfeit products described as AMP plugs, but are not the products of any of the aforementioned suppliers, nor are they even physically similar to the genuine articles. Most of these are low quality SS/WE style plugs, and should not be used with AMP tools.

Suspiciously cheap AMP connectors for sale on eBay. Crystal? I generally prefer plastic. These particular ones aren’t similar to any CommScope plugs and would be destroyed if used in an AMP style tool
A bag of 100 genuine AMP style plugs – CommScope branding

There are two distinct varieties of “AMP” (ish) connector.

  • Traditional or “Line” style (as their documentation refers to them)
  • “High Performance” style
(Left: “Line” style connector (branded CommScope). Right: “High Performance” style connector (AMP branding). Which ever variety you are dealing with, if it doesn’t have the laser etched logo under the tab, and the two indents at the base of the tab, it’s counterfeit)
Left: “Line” style connector. Right: “High Performance” style connector. The high performance style is open inside, allowing the cable to be inserted all the way up to the contacts. More about that at the end of the article.

Example part numbers:

  • 6-557315-3 (Line style, round, 8P8C)
  • 6-569278-2 (High performance style, round, 8P8C)

Since you are here because of differences in tooling, let’s get straight into that. It turns out that these two require different tools:

  • 2-231652-1 (Black dot die) – Crimps “Line” style plugs
  • 3-231652-0 (White dot die) – Crimps “High performance” style plugs
AMP 3-231652-0 (1-853400-0 Die, white dot)
Left: AMP “black dot” die, Right: AMP “white dot” die

Which one is the fabled “AMP” connector? Both varieties are quite different to regular SS/WE plugs, however from a tooling perspective, the “black dot” tool for “Line” style plugs is significantly different. It is this type which other manufacturers sell tools labelled as “AMP” style.

For comparison with SS/WE I’ll be using the Stewart 2990003-01 tool (2990006-01 Die, yellow dot).

Stewart 2990003-01 (2990006-01 Die, yellow dot)
Left: AMP “black dot” die, Right: Stewart “yellow dot” die

When we look at the “black dot” die next to the one from the Stewart tool, the difference is clear. There is a third punch-down in the centre which crimps part of the plug onto the stripped wire, a feature that no other type of plug has. Because of this, you cannot use this tool to crimp most SS/WE plugs.

6-557315-3 plug showing the extra “middle” crimp – specific to this type of connector

As for the “white dot” tool and associated “high performance” plugs, they’re not exactly the same as SS/WE plugs and associated tools but I’ve found that they are more-or-less interchangeable – I certainly could not see and problems with mixing them.

Left: AMP “white dot” Die, Right: Stewart Die

Since we’ve got all of this here – let’s put a clearly non AMP plug into the “black dot” die and see what kind of mess we end up with…

Non AMP plug crimped in “black dot” die

Not a great result, and unlikely to work very well.

But wait! Some non-AMP plugs are actually sort-of compatible with the “black dot” tool

A non-AMP plug, which has space for the wire punch-down

I would’t be making a habit of this. As we can see the wire has been damaged by plastic being squashed by the middle punch-down. Not recommended!

The “high performance” feature

If you care enough to read on…

Left: AMP High Performance plug. Right: Standard “Stewart” style plug

On the left is an example of one, and on the right we’ve got the bog standard alternative. Please excuse the rubbish bit of wire I’ve used here.

In the case of the “high performance” plug the cable is butted right up against the terminals, meaning that there is only a minuscule amount un-twisted cable, whereas the plug on the right has quite a lot.

When we’re running long distances or at 10GbE this matters, but not in any other case.

In summary…

Some (line type) 8P8C AMP plugs crimp onto the cable at 3 points, whereas the rest crimp at 2 points.

I have only seen one other connector type which crimps at 3 points (also originally an AMP specific type – now CommScope) – a special variety of 6 position “long” modular plug which has the lengthwise dimensions of an 8 position plug.

853400-7 “violet dot” die from a 2-231652-7 tool with shielded and unshielded 6 position “long” plugs

These are normally used where a shielded 6 position type is required. Even without this requirement – if you are using 6 position plugs regularly these things are a heck of an improvement over the standard type. They fit standard 6 position sockets, crimp very easily onto round cable, and the longer dimensions and tab make them a lot easier to connect/disconnect.

OMG. It’s a UK (BS1363) Piggyback Plug

So what I hear you say.

If like me you’ve spent any amount of time searching for such a thing, you may have also noticed there is virtually bupkis in the way of such products to choose from.

I come from the land of piggy back plugs: New Zealand. I’ve very much missed their convenience since moving to the UK.

Okay, so they’re not as common in New Zealand as they used to be. Thanks to regulatory crackdowns and changes in consumption habits,  we can say in retrospect the 1990s was zenith of piggy back plugs (or tap-ons as we apparently call them).

Piggy back plugs galore. Without them you’d need three of these socket strips to plug all that in

While the days of popping down the supermarket to buy one are unlikely to return, at least you can still get them on pre-made appliance and extension cords, and re-wirable ones can be purchased from electrical wholesalers.

A selection of PDL “40” piggy back plugs from the 1980s and 1990s – including a couple of examples of the “40A” interrupted phase version

Changes to Australian electrical regulations have crimped Clipsal’s ability to manufacture these items but PDL still makes them (cat# 940).

There are 5 appliances in this cramped domestic data cabinet, but only 4 socket outlets. Two PDL 940 piggyback plugs to the rescue!

But anyway, back to the UK…

A very long time there was a company called Clix who manufactured the first BS1363 piggyback plug (more information here). As those are now collectors items, a modern replacement is desperately desired.

Clix 13A piggy back plug. Credit: Image was taken from forums (stevehertz)

Let’s take a look at the UK’s only purchasable piggy back plug. The seller describes it as a “Surged pass through”, somewhat diminishing the piggybackness of it. Let’s open it up and take look…

Fortunately there are a pair of screws on the underside which let us look at the guts of it. These don’t need to be undone to wire the plug.

We are first presented with a plastic spacer which surrounds the socket contacts, and we can see the surge protection gubbins waving at us down by the neutral pin. This spacer also holds the (pointless) neon light.

Quickly we can see my biggest concern with these plugs. That contact is only just barely on the fuse. I’ve purchased a number of these, and can say they vary from unit to unit. This one isn’t so great. If concerned I’ve found they can easily be bent back into a sensible position with pliers.

But regardless I’d pull that 13 amp fuse out and put either a 3 or 5 amp fuse in its place. I’d not be in the habit of using these plugs with 13 amps.

Lifting up the spacer we can see the socket contacts and surge gubbins clearly. Once again, quality is less than spectacular. I cannot comment on the efficacy of the surge protection. In my opinion surge protection is of little value, and in my case I have de-soldered all of these components, as well as the neon, because all I wanted was a plug.

The one last gripe I have is with two protruding corners on the cradle which catch your screwdriver when you are tightening the line and neutral screws. I’ve clipped them off with side cutters (circled).


Surge protection device? Even if the surge protection is effective, it’s not anything to get excited about. There are plenty of other better made surge protection devices to choose from.

Piggy back plug? Definitely. Why the hell the seller isn’t advertising it as this, is beyond me.

Apparently the idea of such a thing is so alien to the British that it has to have some useless surge protection jazz stuffed in it to make the sale?

As I’ve said the quality of the contacts isn’t amazing, but it is acceptable, as this is the UK’s only piggy back plug, you’ve not got another choice.

If you need something like this – buy a box of them now. Who knows how long these will be available for.

Remembering the PDL 40A Interrupted phase tap-on plug

The final version of the 40A (likely discontinued in the early 1990s) – distinctively coloured white and red

Recently while watching the YouTube channel of UK Electrician John Ward I came across a most interesting clip where an eager viewer from New Zealand has posted in a considerable collection of electrical bits and bobs. Myself originally being from New Zealand it was amusing to watch. Among the collection is a most interesting combination antenna & power socket, which certainly, I had not ever seen before.

One item our enthusiastic mailer of electrical articles has not included, but has made the host aware of, is the subject of this article: The long-discontinued PDL 40A – the de-facto symbol of Kiwi electrical innovation and nostalgia.

Wired with a 4 core piece of red-white-blue flex, an uncommon practice. In this case red is used for phase, and white for phase return

The key difference between these plugs and a regular tap-on is that the phase pin on the rear socket is not connected to the plug side, therefore, using a 4 core cable, the socket on the back can be switched via some kind of control device on the end of the lead.

The underside of a “red-white” 40A. The screw in the centre holds the phase pin to keep it isolated from the rear connector

Typical uses were:

  • Float switches for water pumps
  • Timer switches for lighting or heating devices
  • In engineering environments it is common to find them with a loop of wire attached to the phase pins for attaching inductive clamp meters
  • Anything else you can think of that has to switch a single appliance, without the desire to expend effort fitting a socket to that device
A 40A retrofitted with the back of newer “slim” 40 plug, this particular one wired with a loop for use with clamps meters

While they were designed for use with 4 core cable – ‘Kiwi ingenuity’ is actually another form of the phrase ‘Hook or by crook’ and not surprisingly I have not ever seen one wired like this (that wasn’t wired by myself). Typically 3-core cable is used, then the earth wire gets re-purposed as the phase return, and the switching device has to do without earth. In the case where an earth is connected to the switching device, it’s because the neutral has been done away with, or some other solution is devised that doesn’t involve purchasing a length of  4-core cable.

An early “all-black” 40A found in a typical use-case, a wall thermostat

I find myself wondering if the practice of using these plugs with 3 core cable may have contributed to PDL’s decision to discontinue it. Certainly in the case of earlier versions of the plug which aren’t easily identifiable as interrupted phase versions, subsequently wired with 3 core cable in some unknown likely dangerous arrangement i.e. earth connected to the phase pin – that cable could be mistakenly re-wired onto a metal chassis appliance likely leading to a fatal electric shock.

As expected – the earth wire becomes phase, and red becomes phase return. Our thermostat doesn’t happen to need an earth. A death sentence in the case where this cord is cut from the thermostat and re-used on another appliance by an unsuspecting individual
The top of an older “all-black” 40A
The black 40A. Correctly re-wired (for demonstration) with 4-core brown-black-grey flex

The Australians have got their own version of this – made, of course, by Clipsal.

Clipsal 461SUA – Still manufactured at the time of writing

For anyone wanting this kind of plug, at least these are still made, and certainly, by the time I started wiring stuff it was the only one purchasable. I can say from experience it’s just not the same as using a 40A. While not quite of the same quality – It could be argued that the Clipsal is better, because both the line and neutral are “interrupted”, for the almost inconceivable scenario where an RCD is doing the switching perhaps? Making full use of this does require a rather unwieldy length of 5-core flex, which by the time we get to 1.5mm is pretty big stuff, typical for full load 10 amp applications.

The fact that we’re using one of these plugs at all indicates that we’re not exactly flush for time or money; and in practice I doubt anyone has ever bothered with two pole switching, typically bridging the neutral inside the plug, instead stuffing a couple of lengths of figure eight Christmas tree wire into it, getting us the minimum requisite four conductors.

The innovation of the PDL 40A is frequently complimented by comparatively innovative ways of avoiding purchasing 4-core flex

In this day and age 40As are exceptionally difficult to come by. They were unheard of in domestic environments, and uncommon in industrial / commercial environments too. I got a taste of its rarity when entering an electrical wholesaler with one about 15 years ago, to ask where I could get another: “Whoa!” said the guy behind the counter – “Haven’t seen one of those for a while!” Apparently that day when a 40A was carried into their store was a special one.

The few that still exist are very precious and typically hoarded by obsessive people like myself, a very unusual item to be in possession of indeed considering that I now live in the UK. I can boast a very large collection of 1 (and a broken black one), which is about as many as I’ll ever have.

Will I ever find a use for it? Even if I moved back to New Zealand, probably not.

A circuit for generating 100 Hz or 1 KHz square wave signals

Recently while assisting with an Arduino project, I found myself needing a simple circuit which generates either a 1 KHz or or 100 Hz square wave. The reason for this was to connect to an interrupt pin to generate a timekeeping-level accurate 1ms or 10ms timestamp, which the Arduino its self cannot generate as its crystal is fixed at 16.000 MHz

This turns out to be a little more difficult than I expected. Because you can’t divide 100 down to 10 with flip-flops, whatever you end up building is going to do one frequency or the other, requiring a change in crystal to switch. So first of all, let’s look at which crystals can generate these frequencies:

1 KHz

A crystal that can divide down to 1 KHz must be a power of two, multiplied by 1000. Some examples (all of which are easy to come by) are:

  • 32.000 KHz (divide by 32)
  • 2.048 MHz (divide by 2048)
  • 4.096 MHz (divide by 4096)
  • 8.192 MHz (divide by 8192)

100 Hz

Likewise, a crystal that can divide down to 100 Hz must be a power of two multiplied by 100. These are not so common. Some examples I could find:

  • 25.600 KHz (divide by 256) – I could only find one example from a single manufacturer, which is stocked by some vendors but no longer in production
  • 1.6384 MHz (divide by 16384) – Once existed, but at the time of writing none appear to be in production or for sale
  • 6.5536 MHz (divide by 65536) – Several examples in production at the time of writing, reasonably obtainable

My requirements are:

  • Must be easy to change from 100 Hz to 1 KHz
  • No expensive or obscure components
  • Must be all SMT
  • Vcc = 5V

The next headache

Now I have to find an IC which can divide two of the above frequencies down to 100 Hz or 1 KHz. The trusty old CD4060 immediately jumps out. If we switch between 25.600 KHz and 32.000 KHz crystals, also changing the output stage – we’ve got a solution. Problem is, this solution falls foul of two my objectives – that one-and-only obscure 25.600 KHz crystal, which is not SMT.

With the only practical primary clock (for me) for 100 Hz operation being 6.5536 MHz, that rules pretty much all CD4xxx timers, which according to their datasheets, can’t operate with such high input clocks.

So far as I could see that leaves two options: 74xx292 (Rare in SMT) and HEF4541. If we are to select 8.192 MHz for the 1 KHz option, both can divide by 8192 and 65536, and handle those input clocks.

One more bump in the road

Because of the obscurity of 74xx292 in SMT, I’ve gone for HEF4541. The HEF4541 can in theory have a crystal connected directly to it, but after hours of profanities I discover that running at Vcc = 5V it can’t quite self oscillate at 6-8 MHz. We can prove this by shorting RS and RTC, and we see that it self-oscillates (with no other components) at about 5.9 MHz, which reveals the shortest propagation time between those two pins.

Great, so now we need another IC. Fortunately that only needs to be a 74HC2G04 which is tiny and inexpensive, barely increasing the footprint of this circuit.

The final solution

First, the 100 Hz version. Note that R3 can also be a wire link.

100hz square wave generator circuit
And now the 1 KHz version. R3 is moved, and the crystal frequency is changed.
1khz square wave generator circuit