UK – Experimental Engineering

Posted on December 5, 2016March 27, 2017 by The Engineer — Leave a comment

OpenVPN Server Speed Tweaks

I’ve been running my own VPN so I can access my home-based servers from anywhere with an internet connection (not to mention, in this day & age of Government snooping – personal privacy & increased security).

I’m on a pretty quick connection from Virgin Media here in the UK, currently the fastest they offer:

To do these tests, I used the closest test server to my VPN host machine, in this case Paris. This keeps the variables to a minimum. Testing without the VPN connection gave me this:

I did expect a lower general speed to a server further away, this will have much to do with my ISP’s traffic management, network congestion, etc. So I now have a baseline to test my VPN throughput against.
The problem I’ve noticed with OpenVPN stock configs are that the connections are painfully slow – running over UDP on the usual port of 1194 the throughput was pretty pathetic:

I did some reading on the subject, the first possible solution being to change the send/receive buffers so they’re set to a specific value, rather than letting the system handle them. I also added options to get the server to push these values to the clients, this saving me the trouble of having to reissue all the client configurations.

sndbuf 393216
rcvbuf 393216

push "sndbuf 393216"
push "rcvbuf 393216"

sndbuf 393216

rcvbuf 393216

push "sndbuf 393216"

push "rcvbuf 393216"

Unfortunately just this option didn’t work as well as I’d like, downstream speeds jumped to 25Mb/s. In the stock config, the tunnel MTU & MSSFIX settings aren’t bothered with, some adjustment to set the tunnel MTU to lower than the host link MTU (in my case the standard 1500) prevents packet fragmentation, MSSFIX let’s the client TCP sessions know to limit the packet sizes it sends so that after OpenVPN has done the encryption & encapsulation, the packets do not exceed the set size. This also helps prevent packet fragmentation.

tun-mtu 1400 
mssfix 1360

1 2	tun-mtu 1400 mssfix 1360

After adjusting these settings, the download throughput over the VPN link has shot up to 136Mb/s. Upload throughput hasn’t changed as this is limited by my connection to Virgin Media. Some more tweaking is no doubt possible to increase speeds even further, but this is fine for me at the moment.

Posted on November 20, 2014November 20, 2014 by The Engineer — Leave a comment

uRadMonitor Network

I’ve joined the uRadMonitor network! I’m told my unit is on the way & it should be going live here in Manchester, UK within about 10 days.

This is a crowd project to monitor background radiation levels all over the world, so far there’s a lot of units already online.

More to come once my unit arrives!

Posted on December 12, 2013December 12, 2013 by The Engineer — Leave a comment

Potentially Lethal Clone Apple Charger

I received this USB supply with a laser module from China that I purchased on eBay. I have heard of these nasty copies of Apple chargers going around, but I’d never received one this bad with a piece of Chinese electronics.

Model No. A1265, so definitely an Apple clone. Apparently capable of +5v DC 1A output. Notice the American NEMA pins. This wouldn’t have been any use to me in the first instance since I am resident in the UK & our mains plugs are significantly different, not to mention significantly safer.

Manufacturer is marked as Flextronics.

Here is the charger disassembled. Inside the case these two boards are folded together, creating an alarmingly small isolation gap between the mains side of the supply & the 5v output. Both the low voltage output & the feedback loop for the supply runs over the 4-core ribbon cable.
The mains wiring from the board is as thin as hair, insulation included, so there is a big possibility of shorts all over the place from this part of the circuit alone.

Bottom of the PCB assemblies. Good luck finding any creepage distance here. There simply isn’t any at all. traces on the +350v DC rail on the mains side of the transformer are no more than 1mm away from the supposedly isolated low voltage side.

Plugging one of these devices into anything is just asking for electrocution.

Posted on November 29, 2012May 12, 2013 by The Engineer — 1 Comment

Brightwell Brightstar II BSL4 Dosing System

Here is an old chemical dosing system for industrial washing machines. These units are 4-pump models, with dual pumpheads. The motors are reversed to operate alternate pumps in the same head.

From 2006, this is a fairly old unit, and made in the UK.

Main controller PCB, with interface to the power electronics via the ribbon cable, an external serial port for programming to it’s left. Powered by an ST microcontroller. The LCD is below this board.

Main power supply, sense input & motor driver boards. The PSU outputs +5v, +12v & +24v. The inputs on the lower left connect to the washing machine & trigger the pumps via the programming on the CPU. The motors are driven by L6202 H-Bridge drivers from ST.

Motor & gearbox assembly on the back of the pumphead. These are 24v DC units with 80RPM gearboxes.

UPDATE:
As it seems to be difficult to find, here is the user manual for this unit:
[download id=”5557″]

Posted on October 15, 2011 by The Engineer — Leave a comment

Tool-less UK Mains Plug

This is a standard 13A UK main power plug – with a twist. This one requires no tools to open or connect.
The top cover is slid off the top, after turning the red cam with a coin to unlock it.

Manufactured by Plugco – a Google search of this company returns no results.

Top cover removed from the plug, as is standard with UK mains plugs the live conductor is fused – 3A in this case. The conductors are clamped into the fittings in a row along the top edge of the plug.

Closeup of the wire clamps. Conductor is placed in the slot & snapped closed.

This is an old plug & they do not appear to be available these days, for unknown reasons. Being able to change a plug without a screwdriver has it’s advantages 🙂

Posted on October 4, 2011 by The Engineer — Leave a comment

LED Lighting Part 1

Here I will document progress in replacing standard halogen MR10 lights with LEDs.

These units are from TruOpto, available through Rapid Electronics in the UK. They are 3W total, from 3x 1W emitters on an aluminium back plate.

Here is the LED attached to a heatsink for testing purposes – these units dissipate nearly 2W in heat at full output.

As the lights are to be run from a 12v battery bank, for simplicity a master regulator is required to provide a stable 11.4v rail for LED supply.

I have used a Texas Instruments part – PTN78020WAH. This is a 6A capable adjustable regulator module.

The LED lights are to be fully dimmable – the low voltage PWM dimmers are in progress of being built.

Posted on March 16, 2011March 16, 2011 by The Engineer — Leave a comment

The Truth About DWP Cuts From A DWP Worker On The Front Line

A bit of a shift from my usual content, but I thought this deserved a place for people to see. Only relevant for people of the UK though.

“I’m a DWP worker sticking his head above the parapet and hoping not to get shot…

I work in a busy Jobcentre and my customers are those 25+ who’ve been out of work for 13 weeks or longer. Probably 60-70% of the one hundred or more people I see every week [who] are evidently not fit for work and yet, in theory, it’s my job to whip them through the same hoops as everybody else, persecute them, attempt to stop their benefits and generally shame them into applying for all manner of wholly unsuitable jobs that they’re never going to be able to do.

In reality, what I do is tell them the system sucks and advise them of ways they can stay beneath the radar, or suggest they sign off JSA and move onto ESA and do whatever I can to make the transition as trouble free as possible.

On the other side of the office to me are the Pathways team, who deal with customers on ESA. We all know that over the coming months most of them will be forced to migrate over to the JSA bods like myself and we won’t be able to cope with either the numbers or the particular problems that this customer group represents.

The point of all this waffle is that the policy makers have embarked upon their catastrophic journey without consulting the frontline workers who, without exception in my experience, KNOW that the planned changes CANNOT work.

I would advise people worried about a forced transition from ESA to JSA to be brave and try not to lose too much sleep about it… It’s just not do-able in the real world, there’ll be a horrible mess and people’s lives will face some awful but shortlived disruption and then it’ll be business as usual.

Also, for those who face the indignity of having to venture into a jobcentre from time to time, please be assured – the majority of those who work in them are actually on your side, and have probably less faith in our political masters than you do, and just as much awareness as yourselves that all their vitriolic guff about benefit scroungers and feckless layabouts is simply empty, venomous scapegoating…”

Please feel free to copy and paste this to your own notes/blog, etc. Spread the truth.