Quadrant 3D Printer Cabinet

With the Hackspace having a collection of three different 3D printers and with them all being kept in one multi use workshop, it soon came apparent that we needed a way to keep the dust of of them all whiles also allowing us to gain easy access to them for maintenance. There was an ideal place in the workshop between the workbench and tool board where a cabinet would sit nicely.

With this in mind I took some measurements of the area and make a few rough sketches on paper. The cabinet would be 1200 x 600 x 2000 it would be divided up in to 6 quadrants, the top 4 quadrants will be where the 3D printers would be housed and the bottom two would

3D model of the cabinet

3D model of the cabinet

create storage space for reels of filament and other consumables. At the rear of each of the 4 printer quadrants there would be a 2G plug and RJ45 socket as each of the printers will run of OctoPi allowing the printers to be controlled remotely on the network. Once I had a feel for what the cabinet was going to look like on paper I drew up a 3D model using Free CAD.

 

The material of choice was 18mm construction ply, for the method of joinery I went for rebate joints. Each of the panels that the shelf’s and back would sit in had a rebate grove in the width of the ply routed down the width of the panel at the corresponding heights of the shelf’s the rebate was half the depth of the material. The cut away below shows half of the cabinet and how it is assembled. With the CAD design complete I got to work ripping all of the ply down to size ready for routing.

Cut away of the cabinet showing the rebate joints

Cut away of the cabinet showing the rebate joints


To ensure that all of the rebates where routed consistently I used a straight edge to guide the router on all the parts. By scoring each side of the rebate joints with a sharp knife before routing prevents tear out from the spinning cutter leaving a nicer and smoother finish. For routing the rebate on the perimeter of the back the router was used with it’s fens, the fens was set to the correct width from the cutter to the edge of the work piece and run down the edge.

To assemble the cabinet the shelf’s where first glued and nailed on to the two sides, this step was completed first because  you could only get a run of nails in one side of the middle. The middle and top where then joined the same way followed by the back. After a sand and coat of varnish the cabinet was ready to be moved in to the workshop.

The assembled cabinet in place ready for the doors to be hung.

The assembled cabinet in place ready for the doors to be hung.

Once the assembly was complete I decided to add some pull out shelf’s on rails, this would make it easier to remove things from the print bed and gain access to the back of the printer for maintenance.

door frame glued up

door frame glued up

To make the door frames I created a central groove using a table saw in several lengths of 20 x 35mm PSE timber. This grove would be where the perspex in the centre of the door would sit. The rails and stiles where cut to the correct length and a tenon was made on the end of both of the horizontal rails. The perspex sheet was cut to size and the frame was glued up using a pair of sash clamps. I used piano hinge to hang the doors, this was mounted on to the cabinet first.

The first door mounted

The first door mounted

All that was left to do now was install the rest of the doors, give them a coat of varnish, wire in the electrics and mount the pull out shelves. With the 3D printer cabinet approaching completion there where a few things that I could have done differently and some things that could be improved or even added on. One thing that could be different is the method of joinery, there are a multitude of different ways that it cold be done the other witch I looked in to was finger joints. Finer joints provide a larger surface area for glue to stick to but are more time consuming. I ended up using rebate joints because they where more suited to the design, not only that but would also give me more experience for the next job where I could attempt something a little more complex with the skills I have learnt.

The completed quadrant 3D Printer cabinet with pull out shelfs.

The completed quadrant 3D Printer cabinet with pull out shelfs.

Something else that would have helped during the build process is to have made a jig that could be set over the rebate and clamped down that the router would sit in and slide across, making the process of routing the rebates much more efficient and accurate quicker. A later addition that I intend on adding is a set of castor boxes for the bottom two quadrants witch will make it easier to retrieve consumables. Overall it has been a fairly successfully build. The cabinet itself is very sturdy and provides the purpose it was intended for it also provides more storage areas both on top of the cabinet and down below in the two quadrants.

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For more images please visit here.

The Hunt for J5

Pi Zero J5 Connections

Pi Zero J5 Connections

J5 is alive, and is definitely not called johnny or a robot in a kids sci-fi film. J5 is the mystery connector footprint on the bottom of the Pi Zero. I have been puzzling over what it was intended for since getting my Pi Zero from Pimoroni.  Asking around amongst those who would know more than me about it (Not difficult to find) the hot favourite was a JTAG port but no one was entirely sure and there was no pinout. An extensive google around was surprisingly information free.

Time then for some reverse engineering, first stop was a USB microscope and a look see for obvious pin functions, gotta tackle the low hanging fruit first. Taking pin 1 to be the pin nearest the J5 ID we can see the footprint is for an 8 pin connector and the body or screen is not connected. 1 is the Pi system reset or run pin as it is labeled, 4 and 7 are ground connections. OK that leaves 5 pins to go. I visually traced the connections and lost them in to the maze of CPU via’s. As other than the reset they did not go to the GPIO pins I could rule out an easy hit as to what they were. The up side is if they were JTAG, it would have to be dedicated pins, not GPIO pins, and therefore projects could be debugged even with a phat in place. Hmmm what were those other 5 pins for. Normally at this point I would start on in with a multi meter or a scope and see what I could find out next. But serendipity smiled upon me, in that way it never normally does.

B+ J5 Connections

B+ J5 Connections

Putting some time into a side project (building a Graphite graphing server) I was working with a Raspberry Pi B+. Purely as I tend to mostly use Pi2’s now and was using up any older ones that were lying around. Embedding them irretrievably into other things. Fiddling with the board during one of many mental luls, I noticed the same mystery footprint on the board directly under the HDMI video connector. In fact it is so much the same it is also labelled J5. Cross referencing the ground pin outs that we know from the Pi Zero we get a match. What is more the 5 pins we had not identified are broken out to pogo pin pads bang next to the footprint. All along with nice labels. Combining the data we have then gives us the following table:-

J5 Pin Information
Pin No Pi Zero Function Pi B+ Function Comment
1 Pi System Reset ? Pull low to reset the Pi
2 ? TRST_N TAP Reset pull low to reset the TAP
3 ? TDI Test Data In
4 Gnd Gnd Signal Gnd
5 ? TDO Test Data Out
6 ? TMS Test Mode Select
7 Gnd Gnd Signal Gnd
8 ? TCK Test Clock

Some further technical info on TAP & JTAG can be found here worth a look at to illustrate some of the concepts behind JTAG. OK, all well and good, what is left to do, identify what sort of connector J5 actually is and make up a JTAG lead for it then connect it up and see if we are right.

Simply Crochet Robot

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[Post by SHHM member Sarah Cullen]

I enjoy mixing traditional crafts with tech. A while ago I decided to teach myself crochet, mostly using YouTube and a couple of crochet books. I found a pattern for a crochet robot toy and decided that instead of just crocheting buttons and a light, I’d use sewable electronics instead.

The crochet pattern came from Issue 16 of Simply Crochet.

I used a CR32 coin cell battery holder, battery, sewable steel thread and a large red LED for the light on the robot’s head.
To sew the light on, I pushed the legs of the LED through the top of the crocheted head and then used round nose pliers to coil each leg out to the side, flat against the crochet. On the inside of the head, I stitched from the negative terminal of the battery holder, lightly through half of the thickness of the crochet (so the thread didn’t show on the outside of the robot) to the negative leg of the LED. When sewing through the coil of the leg of the LED, I sewed knots as I went, as the steel thread has a bit of spring to it, and so wants to open up, but this can break the connections in your circuit. I did the same thing, with a separate piece of steel thread, for the positive side of the LED and battery.

The buttons on the front of the robot are a bit more involved. They needed 2 battery’s worth of power and a LilyTiny circuit board to create the flashing. The batteries are connected to the LilyTiny and then the LilyTiny is connected to the LEDs. Although the LilyTiny is designed for 4 LEDs, I connected more, in parallel, as I had more than 4 buttons that needed illuminating. The default patterns programmed into the LilyTiny were fine, so I didn’t need to reprogramme it.

The end result is here:

More LED crochet
I followed that project up with some a monkey & ninja from the Creepy But Cute crochet book and a pirate pattern from the author’s website. Rather than sewing their expressions on, I gave them sewable LED eyes. These were added behind the felt patches that are their faces. The battery holder is under each creature, which has meant I’ve needed to add a ring of chain stitch to the base, to hide the holder and stabilise each creature.

More recently, I made the robot from the Creepy But Cute book. Gee made a small circuit with cyclon style red LEDs that I used for its eyes. As these aren’t sewable LEDs and they’re tiny, it needed the crochet cutting so that they’d show through the felt face. The felt face stops the crochet from unravelling, so no problems there. At some point I may remake this but use a Adafruit Gemma / Flora to control sewable LEDs for the cyclon effect but I’ll need to find the time first!
The complete set is here:

They get taken to Make Faires with Pimoroni and recently featured in Makezine’s photos of the Berlin Faire.

All sewable electronics parts for the various projects came from Adafruit / Sparkfun / Kitronik via Pimoroni.

Inertial Logger Prototype

Prototype Inertial Logger

Prototype Inertial Logger

The prototype hardware for my inertial logging project is built. Lovely you say, looks nice, fits in a small tin, and just like everyone else, you immediately follow it with “What does it do ??”.

This project follows on from a bunch of discussions in the SHHMakers mailing list. Basically the idea is that you can record or log a track that the tin has followed using only sensing of the movement of the tin. The movement of the tin is the inertia bit. Everything has inertia and sensors that can measure that can also infer how much and by how far something has moved. Inertial guidance works on the same principles and is used for quad-copter pilot electronics etc. This is the point at which, like everyone else, you interject “I just use my phones GPS”. But what about those instances where there is no GPS signal. Try Caving, UrbEx, SCUBA Diving, or just simply finding your car in a multi-story, when you have forgotten where you parked it. Maybe you want to know where the tube system really is under the map of a city rather than the schematic map most underground systems give you. These examples are where inertial navigation and logging have a part to play.

“OK” you say “I understand now. how do you do it ?”. If you put on a blindfold and someone manoeuvres you along a track you can, if you concentrate remember it, this is the logging bit. Each time you are turned this way or that you can feel being turned, this is what a gyroscope measures, rate of turning. If you are moved quickly or slowly you can feel that too, this is what an accelerometer measures, rate of acceleration. If you are in a lift as well as feeling the acceleration, you can feel the pressure on your eardrums change as you go up or down, this is what a pressure sensor measures. You can feel if you are outside or inside by temperature changes, this is what a thermometer measures. People who are blind are more sensitive to these things than the sighted, purely as they use these clues to navigate in a world they cannot see. They also count steps. I don’t think this project will be sensitive enough to count steps but maybe it will. It certainly can measure the passage of time against acceleration/rotation and therefore infer distance.

Zoom in to see the contents of the tin

Zoom in to see the contents of the tin

“So what’s in the tin?”. You are bored with explanations now and want to know about the techy bit. If we zoom in to the tin, we can see a 10 DOF inertial navigation board (GY-87) top left. Under that on the left is a micro SD card. In the middle is a Teensy 3.1 micro-controller. At the right top there is an Adafruit Power Boost 5oo Charger. To the bottom right is the coin cell battery backup for the Teensy’s RTC (real time clock). Underneath the board is a 2.5Ah LiPo. The power boost, LiPo and teensy were bought in from our local supplier Pimoroni. The 10 DOF (degrees of freedom, or number of things it measures) board came directly from china via AliExpress. The power supplying arrangements are a compromise that niggles somewhat. Whilst the LiPo has plenty of power, all the other components actually run at 3v3. the conversion from 5v to 3v3 is done locally on the boards using linear regulators so we are wasting nearly as much power again as they draw. Unfortunately linear regulators dump the surplus energy as heat, far from ideal in a closed tin. Particularly where we want to be able to measure the temperature as part of your logging. Altogether though an adequate first pass for prototyping and testing purposes. There is a bit of a learning curve to be climbed and this is a reliable way to do it. The 10 DOF board has 3 axes of Magnetometer, Accelerometer and Gyroscope on-board as well as an air pressure sensor for us as an altimeter, giving the 10 things or DOF it can measure.

“If you were doing this again what would you do different ?” you ask. Well bearing in mind that I acquired the parts for this a bit back and they have been gathering dust the purchasing decisions would be different. I would be replacing the hand wired SD card holder and Teensy with a Pi Zero. But have to add an RTC. Also I would get rid of the linear regulator on the 10 DOF board and power it form the Zero’s 3v3. Just to move the self heating away from the air pressure sensor which relies on an internal temperature measurement for air density compensation. I would probably add a press button on the outside of the case so that way-points or events could be marked in the track log. Useful for overcoming cumulative errors. One last thing, inertial navigation chips and managers are a field of rapidly advancing technology, many of our smart phones already have them inside. The inertial sensor chips themselves are becoming ever more integrated placing it all on one chip together along with local processing to make them ever more accurate. So something to watch out for and periodically check the current state of play.

The firmware for this prototype is available from my git hub repository https://github.com/AndyKirby/Firmware/tree/master/InertialLogger please note it is a work in progress rather than a finished item.