Polarshield v2.4 compared

I got a pile of boards back from the maker recently: Polarshield v2.4 (https://github.com/euphy/polarshield_hardware). Here it is alongside the 2.2 version (on the left)  to show the progress.

Polarshield v2.4 (compared to 2.2)

Not much right? There’s no revolution, indeed, but a couple of minor changes that makes it easier to build.

  1. More surface mount parts. The tactile switch in the top-left is now surface mount. SMT parts are just quicker to work with.
  2. Moved the microstepping jumper solder pads to the back of the board, and freed up a load of space.
  3. Squished four of the 1k resistors into another 4-row resistor network. This is the smallest part I’ve ever used, 2x1mm, you can barely see them on the picture. There’s one between the two motor driver sockets, and there’s another below the stack of LEDs on the top-left. This makes pick-and-place much faster. I’m not convinced the super-high density was a good idea though – it is far less tolerant of sloppy placing / solder paste application. We’ll see.
  4. Better designed for soldering with hot air, and iron. Some of the traces on the board were sometimes difficult to heat effectively, without also over-heating the component. The electrolytic capacitors were particularly problematic. I’ve routed the traces less efficiently in some cases, so that they have more copper that I can heat with the hot air pencil.
  5. LEDs are all orientated in the same direction. The old board has them pointing everywhere, so I was always spinning the board around. v2.4 has the anode to the right-hand side in every case. It’s to reduce the chance for placing errors.
  6. The holes for the DC power jack are placed off-centre, so the solder tabs are a friction fit. It makes the part self-aligning. Nice work sparkfun!

And the great thing is, it works, ha!

I’ve been taking some time off the Polargraph shop lately, because of work pressures and a couple of other things. It’s been really nice not to have to rush to the workshop every hour of the day to keep on top of things, and I’ve been able to do a little development here and there.

I think I’ll be back eventually, but maybe in a couple of weeks, and I might try a different manufacturing pattern.

Labelling evolution

My manufacturing process is always sometimes evolving. It’s not a complicated one, but there’s enough steps and nuance that I benefit from reminding myself what I’m supposed to be doing.

A run of bad Polarshields last year prompted me to start being a lot more careful about how I assembled and recorded the assembly of them. I started putting little journals on each one, which were just a strip of sticky tape with any story on them. Anybody who bought a Polarshield will have found such a thing.

Quality control labelling on Polargraph gear

I recently kicked myself a couple of times in a row when I thought I’d forgotten to test a certain aspect of the board, and had to open up a pile of sealed parcels to find out. Fortunately in that case, there was no problem, but I made up some new labels to help me not make a mess in the future.

The evolution is in the pic. The QR takes you to Building a Polargraph from a vitamin kit on the wiki. The final version is less handsome, but more useful, and there’s a beauty in that trade-off.

I like seeing these kinds of “work in progress” pics on other makers’ blogs.

Polargraph at the Edinburgh Science Festival 2015

Once again, the Polargraph Pro is featured as part of the Edinburgh Science Festival’s Making It touring exhibit, stationed until the 19th of April 2015 in Ocean Terminal Shopping Centre down the road in Leith.

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Tricking the machine with smartphones

I was a bit nervous about having the machine presented in such a uncontrolled environment (it was in the National Museum last year), but it’s been remarkably low-maintenance during it’s first week.

Some better than others

Some better than others

For this year’s outing, there were a very small number of changes to the firmware, mainly to add a feature to support a button and an indicator LED on the circuitboard that is controllable via commands, and used to signal to the Science Communicators that it needs it’s paper changed.

The changes to the Polarweb controller software are a little deeper, and there’s now a visualisation video stream published to a browser so you can see what the machine sees, and what processing it’s doing. Worked pretty well, but taxed the original laptop a bit much (it was an Atom), so the machine has been upgraded.

Other upgrades:

  • Minimum face size, so only people close-up get recognised and drawn
  • Path sorting to make for more efficient drawing (I hope to pull this work into the general Polargraph Controller some time soon)
  • Except for changing the paper, there is no manual intervention required during operation
  • Tracing controls are available in the interface to change posterisation levels, minimum path length, maximum path count and smoothing
  • The pen lift servo wire is routed more neatly, and uses spring-loaded retractable cable spools rather than the coiled cable that got stuck all the time
  • Drawing sequence can now fixed bottom-to-top so that pictures can be cut out and taken home as soon as they are drawn

How to make a PolargraphSD

Just thought it might be interesting to see the steps that go into making a PolargraphSD. I’m curious about this kind of stuff, and I love work-in-progress pictures. So I assume you do too.

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Apply solder paste.

Starting with the PCB mounted in a jig made of other PCBs, I use a plastic stencil, and a card to squeegee on the solder paste. This can be messy, but it’s very fast, takes less than a minute for each one.  I have taken to making up batches of 10 polarshields at a time, it takes a reasonable weekend, or a long day from beginning to end.

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Sometimes bits get missing, or I accidentally rub off the paste during placing, and I use a little syringe to do touch-up stuff. Afterwards, there’s these nice little pillows of paste on all the pads.

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Pick and place

I’ve got all the parts I need in little boxes, and empty out about the right amount of parts, sort through the pile and turn them over and line them up with a pair of tweezers. I used to use tweezers to place them too, but have recently got a cheap vacuum pickup tool that makes it a bit quicker.

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Using magnifiers and good lighting, dealing with these tiny parts is much easier than I thought it would be.

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I place most of the ICs with tweezers, because I get a bit more control over their orientation – they have a tendency to swing around a bit on the tip of the vacuum. The really big parts (electrolytic caps and the inductor) are just placed with fingers.

Soldering / reflow

I’ve got a hot air gun (Atten 858D+) that I used to take 8 minutes to melt all the solder paste on each board, and I still use that for touch-up and fixing. The last couple of batches of Polarshields have been soldered with a little home-made reflow oven though. This is a mini oven, retrofitted with a Zallus temperature controller. The temperature controller was a Kickstarter I backed at the end of last year, and it seems to work really well. Though the whole contraption looks like junk – but that’s my fault.

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The boards go in two at a time, and cook for 6 minutes, releasing all kinds of (probably deadly) fumes. I only use lead-free solder in all my stuff, so it’s not the nice smell you get out of rosin-fluxed lead solder. I miss that. My old tutor told me that eating plenty of jam would help ward off the poisoning that we would all get off the solder fumes. I like the story.

Now comes the really boring bit.

Through-hole soldering

There doesn’t seem to be any way to short-cut this one, just got to cut lots of parts to length and solder them all in. Using the kind of small iron tip that is useful for touching up SMT work makes this an absolute misery, so use a big clumsy chisel tip instead to whizz through.

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There are 156 points of through-holes to solder. During soldering, I sometimes spot things like this:

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There’s a solder bridge between the first three pins of the IC. This is irritating, but out of 10 shields, there’s normally four or five bridges like this that need a touch-up. Fix it with some solder braid. In this case, I noticed the IC was a bit skew-whiff on it’s pads too. I am not sure if it is something about the heating profile, but it seems like the parts don’t always get “pulled” onto their pads by the solder tension during flowing. At least, not as straight as I saw when I was using the heat gun. So with this IC, I reflowed it using the heat gun, and just nudged it to straighten it up. Afterwards, I wash the board with Techspray Flux remover to clean it up. Add stepper drivers and LCD, and it’s ready to test.

Testing

Upload the latest version of polargraph_server_polarshield and see what happens. Well, I just got a white screen. So I took another look at the board and spotted another solder bridge. Fixed it.

Testing involves plugging in a couple of steppers, a servo and an SD card and running a test script from the card. If the motors move smoothly and quietly, and the servo wiggles, and the LCD responds to touch, then it’s cooked.

IMG_0043_c_pFor full PolargraphSD kits (with the motors and cables), I do another test of the same routine before I pack everything up, to make sure the particular motors and the cables are correctly constructed, and they all work together.

Case

The case is made up of 16 laser cut parts, and is fastened together with six M3 nuts and bolts, tab and slot style. I try to leave as much of the protective film on as possible during assembly.P1050604_c_pI enjoy peeling that stuff off when I buy a new product, so I assume other people like it too. It stops my grubby fingerprints spoiling it too. I’ve got white gloves and everything, for this bit.

So now you know. Tune in next week and I’ll show you something equally as thrilling, how I clean my oven or do the hoovering or something.

 

 

Slow going

Slow going, but … going!

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The hardware is working fine now, working with all kinds of SD cards, all servo motors and all power supplies, but I’m waiting for the full set of the new cases to be cut and sent.

The case is funny. Probably the ugliest thing I’ve ever made, but I quite like it.

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Choice between clear acrylic and MDF – any thoughts? The clear looks shows fingerprints but looks pretty snazzy.

 

PolargraphSD progress

The PCB v2 testing is still ongoing, the end is closer and I’m expecting the final boards late next week. This extra round of board testing was always accounted for in the schedule, but what I didn’t account for is the last set of PCBs taking three weeks instead of one week to arrive. So although I feel this is disastrous, and the project is crashing down around me, actually it’s only literally two weeks behind, and I just need to get a grip.

I know that’s not much consolation to those of you who have been waiting since February, and I am really sorry about that, and that’s the bad news.

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Why

I’ll do a proper introduction when it’s done, but in short, the Polarshield v2 has an integrated switch-mode step-down power supply so that the arduino can be run safely from a single higher-voltage power supply, without overworking the arduino’s on-board voltage regulator. That’s all gone fairly smoothly. This makes the system much more tolerant of working with cheap, basic arduino clones.

The second feature is fixing the circuit that converts the arduino’s 5v signals to the 3.3v signals that the screen and SD card expect. Previously this used resistor networks, but I’m using logic buffer chips now. This should make SD cards from different manufacturers much more reliable. BUT, it is new to me, and that’s why I’m determined to make a mess of it.

For those who are interested, the PCB files, and the gerbers that go to the PCB house are in the repo at https://github.com/euphy/polarshield_hardware.

Parts are slowly rolling in

A big lovely batch of shiney stepper motors arrived today. My electronics parts came last week (£650 of ICs and connectors – that is always so disappointing to receive). I’ve got a pile of touchscreens, and stepper motor drivers, and a big bag of drive sprockets. A big box of MEGA2560 R3s. Red ones.

The first version of the Polarshield v2 was tested and found wanting, so I’m expecting the samples of the final version at the beginning of next week. The first batch of PCBs took a week to arrive, this batch has taken three weeks so far. I am looking for a new supplier.

So unfortunately, that has eaten up all of my contingency, and then some, and so I’m already behind before I’ve even started. Great!

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Polargraph Pro Preview

Hello, I’m getting excited about the new Polargraph installation that’s been eating up all my time recently. IMG_20140327_160058025_HDR This is part an exhibition called Making It, itself a feature of the Edinburgh International Science Festival, and it’ll be running in the Grand Hall of the National Museum of Scotland, here in Edinburgh, for most of next month (April 2014).

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I’m just putting some finishing touches to the machine and the control software.

There’ll be more of an update when it’s up and running.

Pre-order PolargraphSD v1.8

I’ve just made a listing for the PolargraphSD v1.8, over at the Polargraph Shop.

The price of it is likely to be the same as the last round, but if you want to pre-order at a decent discount, you can put a 25% deposit down to hold your place in the queue as well as make cash flow a little more predictable. It’s a kind of micro kickstarter. I hope to have this ready for shipping in May, but it’s more likely to be June.

I hope to enlist an extra pair of hands to help me assemble this time around, and am having this semi-formal fund-raising period so that I can buy a few critical parts in a full-sized batch (ie 50), rather than buy them piecemeal over the run of the batch. That ended awkwardly last time, with delays and malfunctions a-go-go.

Edinburgh Science Festival Project

I’ve been asked to make an installation as part of the Edinburgh Science Festival in April, so that’s the project that’s eating up my time at the moment, and the reason for the halt to PolargraphSD manufacturing.

This thing is going to be great though: Two large portrait machines, continuously drawing faces from a kinect / webcam on rolls of paper.

I’m using a Teensy rather than an Arduino for this project, EasyDrivers and optical encoders to close the loop and keep track of position. This will make for a more robust, semi-automatic machine. I hope to have endstops too, and a good presentable gondola that can take a range of fat pens.

I also hope to be taking one of my machines along to the Mini Maker Faire that closes the festival at the end of April.

 

Pause for thought. And breath.

I’ve got half a dozen Polarshield PCBs left, but I’ve marked them as “sold out” in the shop.

I’m tired. I’ve had a few technical set-backs recently, that would be merely irritating if I was only make two machines a month like this time last year, but it immediately escalates into a full car-crash when I’m making a dozen a month – there’s just no room for mistakes, all the stakes are higher, and things move faster, sell out faster, need more careful management and delays cause more people at a time to be annoyed.

Not a bad problem to have? Well that’s true, poor me, boo hoo, there are worse problems, and I genuinely thank all my customers profusely, and everyone who has joined in on the forum and by email – actually by far the best bit of the project.

But I’m going to work to get this last problem sorted out (accursed SD cards and power management, I do bite my thumb at thee), and then pause my sales and manufacturing department (that’s what I’m calling my hands this week) for a bit to review the project as a whole.

I have an installation to work on in February, which will hopefully be presented as part of the Edinburgh Science Festival in April, and should be jolly exciting, and result in some neat new pieces of tech and software – encoders and a proper library at last! Right now I would not be at all disappointed if that was the last Polargraph machine to roll off the production line – the last of the V8 Interceptors, as it were.

However, let’s be realistic, I suspect the lure of the humming motors, the clattering of beaded cord and the pleasure of visiting my favourite post office lady will soon bring me back in, and … with upgrades.