Sunday 26 July 2015

A quick tour of the Sheffield UTC (University Technical Collage)

The other week I was invited on a mini tour of the University Technical Collage (UTC) in Sheffield. The UTC is a school for kids aged between 14 and 18, with a focus on technical and creative subjects including Engineering, Game Design, 2D/3D Design and Industrial Processes. This is alongside more regular subjects like English, Maths and Sciences.

The facility is a combination of new and old, parts of the building being the sympathetic resorted Sydney Works the site of Sydney Silversmiths and a brand new build.  

The reason I had been given a tour was to loan out some WS2812 and LPD8806 addressable led strips for there up coming Prom.  

This is the 'Multi-purpose Room' where it was to be held and spent a few minutes scratching our heads on how to get the LEDs into the gantries and how to power them.

The  amount of computing facilities is quite amazing with both PC and Mac facilities. Though I do find myself cringing very slightly at a room full of Macs.   

Some of the computer suites have dual monitors this is the game design room where the students make games and graphics using the Unreal engine. This is game engine is being used currently to create games so definitely promoting up to date skill sets.

 The UTC has a very good compliment of manufacturing equipment including mills, lathes, routers and laser cutters. As well as plenty of opportunity for students to get there hands on and build 3D printers of many types including fused filament and liquid resin SLA printer like the FormLabs Form 1.       

Then I was shown my favourite room of the whole tour the mini factory room.

This room is filled with Festo industrial processing equipment the same as could be found in any automated production facility WOW.   

This proper equipment with real industrial control look at them PLCs.  

Even a 5 axis Mitsubishi robotic arm to load parts into a CNC mill. 

Dealing with real axis, sensors, conveyors and stuffs. 

There is also equipment for liquid processing and mixing.

This is one of the Festo pneumatic workstations for that students can use to design airflow systems. The shiny blue and brushed aluminium of the Festo kit is very familiar as the Pick and Place machine that I operate at Pimoroni uses the same valves and vacuum generators. In the background you can see a Delta 3D printer built and maintained by some of the older students. 

'Be Creative' I'm sure I've tweeted that before, Totally in awe of the place and find myself wishing the collage I went to was like this. :)

This is a School that is well ahead of the curve, teaching up to date skill sets and with mentors from real creative businesses it's helping the next generation to go and MAKE STUFF!

Thanks to the Staff of the UTC for the tour It was inspiring.


Saturday 18 July 2015

Dirty Circuits Done Dirt Cheap

Often design and research is and expensive business, especially when dealing with technology that your are unfamiliar with. A big proportion of this is PCB manufacture and I have spend a few years looking for a low cost reliable method for PCB production.

The most cost effective method is to have the boards produced overseas but then you won't be sure of the quality of the boards until they return. This is where Dirty PCB step in.

Dirty has been setup by the guys at Dangerous Prototypes as a reliable access to PCB fabs overseas.

I discovered Dirty PCB while looking at another PCB manufacturers reviews and recommendation on a forum post.

So went over to there website and I was almost knocked of my feet at how cheap 2 layer PCBs were.

If you can keep your design under 5cm x 5cm and don't mind if you end up with anywhere between 8 - 12 PCBs then it is only $14 (9GBP) that could be less than 0.10GBP   1GBP per PCB. WOW! There is also a selection of colours for the solder masks at no extra cost.

For me that is great for me as most of my designs are under this size as 50x50mm is quite equate for a breakout board but for $11 more you can have up to 10cm x 10cm (100x100mm That's huge). 

There are a few things that you need to accept to get this price level the boards can only be 2 layers and the pad finish will be HASL (Hot Air Solder Leveling) there is an option for ENIG (Electro-less Nickel Immersion Gold) but it is $15 more. Also there free postage option is quite slow so its worth paying $19 more to get DHL airmail, I realise this is more that the PCBs cost but otherwise it could be a up to 8 weeks delivery. 

Next thing to have a look at is there capabilities, this is all listed in the FAQ.

MaterialFR-4 0.6mm-2.0mm 1oz copper ('standard' PCB material is 1.6mm thick, but we default to 1.2mm)
Layer number2L
Maximum size100*100mm (10*10cm)
ShapeAlmost anything! We'll send it and see if they accept it!
Min internal slot32mil (0.8mm)
Min core thickness4mil 0.08mm
Min core thickness16-96mil(inner) 16-118mil(out)
Min w/s5/5mil(I/L)
Min w/s5/5mil(O/L)
Min silkscreen line0.15mm
Min BGA sizeOblong:10*13.5mil/circle:12mil
Min SMD width8mil
Min solder dam3mil(green)/3.5mil(black)
Min dielectric thickness2.5mil
Min diameter of finished hole12mil
Tolerance of drill position+/- 2mil
Tolerance of finished hole sizePTH +/- 3mil
Tolerance of finished hole sizeNPTH: +/- 2mil
PTH hole copper thickness0.6~1.4mil
Max A.R of PTH8:1
Surface copper thickness1oz
Routing dimension tolerance(Z0) Impedance control 4mil
V-cutNow refused! 80*80mm(min) 380*300(max)
(Z0) Impedance control+/- 15%
Ionic contamination< 6.4ugNaCl/inch2
Surface treating(No PB) hot air levelling/AuSn/AgCN/Electrogilding/Ni/OSP*/G.F
*OSPOrganic solder-ability Preservatives
This is much the same as most board houses standard service I'm mainly looking at the trace thickness and clearance which is 4 thou (thousandths of an inch, this is a bit of a legacy thing with board houses) and a clearance of 5 thou.

There is some helpful things further down the page, Dirty PCB supply a design rules check file for Eagle this file is use in you design rules check to make sure your PCB design is manufacturable. They also supply a cam processing file to help export your design manufacture file. But if you use Eagle like I do you can just send in your .brd design file and Dirty PCB will do all the exporting for you. This is great as I don't have to worry about getting the export wrong or sending the wrong layer files.  

So that's it time to give them a spin. Note: Dirty PCB only accept PayPal payments best to make sure you PayPal details are upto date.

On thing I noticed after putting in my order is that the level of communication is amazing are reassuring, and you can also check the status of you order in the websites status page.  

One Week Later (seriously that is really really fast!)

Such Box! Much Cute! 

There is no mistaking this box the end stamp is very cool.

And then you even get a sticker, I like stickers :)

The PCBs where well wrapped but a little loose in the bag the could rub against each other possibly scratch the finish but this didn't happen in my case. 

I always get excited to see one of my own designs as PCB please don't get too excited this is not a product its just a demo board to try out a BLE chip that I might use in a product ;)

The finish is great the Silkscreen is legible and the resist is nice and even. lets have a look under the microscope.

The quality is excellent and precise the soldermask is tight to the pads with none of the ground fill exposed. The thing that really knock me off my feet is they have also managed to apply the mash between the the pads on the main package, these gaps are less than 0.2mm in width that is brilliant.

 And for the free sticker.

Got the perfect place for that.

So what do I think of Dirty PCB here is my round up:

  • Easy of use: Straight forward and quite fun the site feels as though it doesn't take itself to seriously and approachable. Though more payment options would be a nice addition.
  • Communication: Reassuringly comprehensive without feeling like I'm being spammed.
  • Lead Time: Quick! 
  • Packaging: Exciting!
  • Finish and Quality: Astounding good.
I can only award Dirty PCBs up to 5 sparks but in may opinion they deserve 6. Very pleased with the service.


Monday 6 July 2015

Hacking the RyanTecK Debug Clip

I recently Acquired a RyanTeck Debug clip and in a previous blog post I assembled and set it up.

It work brilliantly with the Raspberry Pi but I would like to use it in some of my other projects and put it through its paces or at least the USB bridge IC the MCP2221 by Microchip.

The first thing I want to do is hit the data sheet and see what other functions the MCP2221 is capable of.

OK, Ryan Tech I have to admit this chip is really cool I hadn't noticed that it has an onboard ADC as well. This is all on top of the standard GPIO, UART and I2C capabilities. 

Hack #1 

Soldering a header into the the debug clip. This is mainly so I am able to use jumper wires to hook it up to other devices. 

For me I find female socket most useful for the stuff I like to mess with. This just allows to make the connections  mainly the first one being connecting the power so the debug clip can run without being attached to the raspberry pi.

Hack #2 

Powering The debug clip without a raspberry pi. The Debug clip has a voltage fail safe mainly for the Raspberry  Pi. The MCP2221 runs from the 3v3 voltage rail of the RasPi but this also means it will not run on its own. 

This is fixed by using a a jumper wire between the 5v connection and the 3v3 .

WARNING: This will mean the debug will be running at 5v do not connect to the RasPi's or other 3v3 devices GPIO It could damage it. This is why I use the socket and jumper wire without soldering at the moment. 

Hack #3

This is a bit of a dirty hack to get the 3v3 power onboard. I have a few  AP1117 LDO 3v3 voltage regulators. I'm going to hack one onto the underside of the board this will give me a selectable  3.3volt supply.


A few flying decoupling caps as recommended in the application notes. A bit of jump leading on the to and all is well.

Now the UART is running at 3v3 again without a raspberry pi. and now running with a Ublox Neo-6M GPS module.

With some nice tangible data returning to putty. I'm doing this indoors so I don't have a GPS fix but the data connection  work very well.

Further hacks

There will be more hack coming with the debug clip like changing its function and using the I2C interface, and this little device is sure to make an appearance as useful tool in future posts.

Happy Hacking  :)

Sunday 5 July 2015

What makes a DHT11 temperature humidity sensor Tick

A DHT11 is very low cost and well supported temperature and relative humidity I've had a few of these for a while and always wondered how they work. I think its time for a TEARDOWN.

There are a lot manufactures for the DHT11 this one is made my AOSONG. It can run between between 3 and 5 volts and uses a simple one wire protocol to communicate with other devices. For more details on the sensor itself check out the datasheet.

The casing is in two parts so to get inside it is just a matter of getting a sharp knife and splitting the case apart.

Inside the case is a small PCB with a SOIC 14 packaged IC unfortunately the part number has been removed so there is really no way to tell if this is a custom part or a specially programmed MCU. along the edge of the IC are couple of  ceramic capacitors for decoupling and noise suppression, and some other misc passive components. The green resistor I can assume is a precision resistor for the humility sensor (explained in more detail later).  

On the other side the sensor hardware itself. This consists of a PCB with interlaced traces that creates capacitance this with change based on the amount of moisture present in the air around it.  


The interlaced +ive and -ive traces allow a small amount of charge to be stored in each of the traces allowing the circuit to charge up a little, this is called capacitance and this is effected by the material separating the +ive and -ive which is mostly air and its airs permittivity one of the factors for calculating capacitance is affected by temperature and humidity
So the chip uses the precision resistor I mentioned earlier and measures the discharge time through that resistor to calculate the capacitance, and then uses that figure used with the internal temperature sensor inside the main IC to calculate the relative humidity.