About roddersblog

Hello, welcome to my blog site where I would like to share some of the stuff that interests me with you. I am a 40 something electronic engineer living in the United Kingdom - my current job is Software Development but my real interest is electronics and I have a home/hobbyist drive to make stuff. I am also a member of the Institute of Engineering and Technology. I hope you enjoy reading some of the material I post on my blogsite. If you want any more detail please just drop me a request and where possible I'll help you out. I'm a programmer in C, C++ and VB.net and have recently had a look at the Arduino range of boards however I still prefer using the PIC Microchip range of microcontrollers and doing the design from scratch (often in assember). I try to make everything on a limited budget so I often experiment using materials in different ways - I find building supply outlets often give the best value 'per unit weight/length of stuff'.

Do I Need A Google Account?

I’ve a fairly new mobile phone and it is no surprise it is powered by Android (the only other choice of OS would have been iOS – between them they have 99% of the market). The phone is great. Android is great….but perhaps a little too great for my liking.

Having used the Maps and enabled location I would later visit somewhere only to be prompted later with questions of “Did I go into X pub” ? “What did I think of Y place”? and “Is Z your place of work”?

This started to overstep my personal boundary of what I was after. So, knowing my Google account was separate to the actual phone, I removed the account to see what I could still do. The answer is actually quite limited. For starters I can still use Google maps to navigate point-to-point, I can still search the www, I can ring and text people.

android

But the contact names have all been lost – calls are just numbers which makes things awkward. Also the To-Do-List doesn’t work. What does annoy me is that the basic Android does not allow a simple phone-book as standard. Saving contacts prompts me now if I want to save them to my Yahoo account.

A friend said that I should just download a third-party phone-book app. Trouble there is that the PlayStore doesn’t work either without a Google Account. I’ll have to try out the AMazon store or one of the other free app repos.

What I’d really like to do is write my own using Android Studio, add some encryption, add some notes etc. When I manage that I’ll post the results here 🙂

 

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Making a 3D Printer (cheaply) – Linear Bearings

This page is to record all my detail and findings on using linear bearings (good or bad).

Using 8mm rod salvaged from old printer/scanner:

This rod measured 7.98mm diameter.Its leading edge was chamfered and it was lightly oiled with a low viscosity oil.

Cheap Ebay LM8UU 8mm bearings.   There was a high level of friction which decreased after working the bearing back and forth. This however grooved the 8mm rod. I raised this with the Ebay seller who instantly offered me a refund and said they would inform their suppliers…top marks to that seller. A few days later whilst inserting the rod for other tests I ended up with some small ball bearings in my hand !

Hot Melt Glue.    I extruded holt melt glue from a gun directly onto the 8mm bar and when it had set I gave it a sharp tap to free it. Initially it seemed to work really well with little friction. However when left standing for an hour or so the friction increased dramatically. After it had stood overnight I couldn’t budge one of the test pieces. I can only assume the glue absorbed some of the oil and swelled. After freeing up the friction dropped back down again.

Glass Fibre and Hot Melt Glue.   Wrapping a small amount of glass fibre plasterers scrim (which is what I had available) around the rod, making sure the self adhesive side faced out, I was then able to add a layer of hot melt glue. This worked well and didn’t appear to ‘swell’ up like the pure hot melt glue bearing did. I also made a test pice by potting the above sleeve into a short length of copper pipe using epoxy resin.

Polyethylene (PE) Sleeve.   I took some from an old milk carton as I know that stuff has a low friction coefficient. I initially tried wrapping a slither tightly around the 8mm bar and adding hot melt glue. This didn’t stay tight and the hot melt glue didn’t adhere to the PE very well. I tried super glue….which didn’t take at all (that’s a good sign).

Then I tried heating the PE after wrapping around the 8mm bar. This was in varying degrees of success and needs looking at further. The PE melted on some to make a good bond to the layer below. Sometimes on cooling the PE sleeve was too hard to move.

My last attempts were using a sleeve of PE wrapped around and melted using a hot blade (heated in a candle flame). This held the PE slither at the correct tightness to the 8mm bar. I then wrapped around some glass scrim (as that stuff doesn’t stretch) and coated that with some hot melt glue.

This sleeve has low friction and doesn’t have any noticeable play.

..pictures and other notes to follow.

The rest of my 3D Printer build can be found here

 

Making a 3D Printer (cheaply) – pt 2

The parts ordered from Ebay kept arriving and the only bits still outstanding are the 8mm steel rod which unfortunately is needed quite early on.

I cut an old sheet of 15mm Medium Density Fibreboard (MDF) to make the frame and a large base sheet and used wood glue, screws, clamps and Gripfill to joint it all together. As MDF has very little strength to resist splitting when screws are driven into the sheet side on I made sure all were drilled with a suitable pilot drill. I also used very coarse thread screws – they were plasterboard/drywall screws. I also added some 4″x2″ sawn timber to add weight and stiffness to the frame. To add further stiffness I added some triangular fillets to the back of the frame (as seen below).photo_2017-02-22_15-08-07

I had planned to use simple aluminium angles to hold the 8mm smooth bars at the correct height but soon realised that fixing them directly to the baseboard would give me little allowance for fine adjustments. I realised that the original Prusa i3 with its threaded rod was the way to go…but I didn’t have access to a printer to make the corners. Instead I decided to use some old scrap 25mm box section steel (bit rusty) to make the corners. These looked like this:

photo_2017-02-26_12-02-30

I ensured the bottom face was filed perfectly flat. Then I measured from the bottom face to centre punch and drill the holes. As the steel is about 2.5mm thick I drilled each face rather than drill through both faces (as this can cause the drill to wander). The final holes are 10mm diameter to accommodate the 10mm threaded rod. The shorter bars are 250mm and the longer ones are 500mm. I bought the threaded rod from a UK shop called Toolstation

I still need to slot the tops to accept the 8mm smooth bar – which still hasn’t arrived.

The whole frame for the Y-axis, loosely assembled, looks like this:

photo_2017-02-26_12-02-20

I’ve also started to look at the print bed – I’ve used a square of 15mm MDF for a start and mounted the 15mm pipe clips on all four corners.

I had a 8mm rod from an old scanner and chamfered the end and lightly oiled it before putting it into one of the LM8UU linear bearings. I was upset to find they didn’t run anything like as smoothly as I would have hope or though they should. After a few passes they became easier to move but I then noticed the rod was getting badly grooved. Searching the internet it would appear this is a common problem – I wish I had bought some bronze bushes instead. Therefore, trying to keep the costs down I tried to improvise a linear bearing. I made one from hot melt glue and it seemed to work fairly well (centre/right below).

photo_2017-02-26_12-02-39

I also tried wrapping some glass fibre skrim around the rod and them adding hot melt glue. This also had a lower friction than the LM8UU bearings. Finally I tried potting hot melt glue into a short length of copper pipe. These were accurate and at first appeared to move freely. However after being left for a hour the friction increased vastly and they were difficult to move at first until the friction was broken. I wonder if the hot melt glue absorbs the oil off the rod and expands slightly ?

Also see Part 1 of this build

 

 

 

 

 

Making a 3D Printer (cheaply) – pt 1

Aim: to build a 3D printer with my daughter. We don’t currently have one, don’t know anyone with one and have never used one…therefore we might have a few difficulties to overcome but here goes.

I had already heard about the great RepRap movement and straightaway decided to utilise that vast community to ensure our build was cheap and easy. Looking at the RepRap wiki pages we soon decided on the Prusa i3 and looked at how it was built. We particularly like the box frame version as shown in the picture below ( from the RepRap wiki by Bitflusher ) see http://www.flickr.com/photos/prusajr/8127635345/sizes/z/in/photostream/

i3-boxframe

This would be a really good start as we have a half used sheet of MDF that needs using up. We scoured Ebay and Amazon for the bits we needed always thinking of alternatives. Our plan is to cobble together a working printer and then print to parts to improve it – a self-improving 3D printer. Parts orders so far are:

  • 8mm steel bar
  • GT2 belts and 2x 12 tooth pulleys (X and Y axes)
  • 10x LM8UU Linear Bearings (for X,Y and Z slides)
  • 2x 624ZZ bearings (for X and Y tensioners)
  • 5x NEMA17 stepper motors
  • 1x RAMPS 1.4 system, Arduino and LCD display
  • 40W/12v ceramic heater (for hot end)
  • Thermistor
  • 1x 1.75 to 0.4mm brass nozzle
  • 1x M6 Pneumatic connector (for hot end)
  • Some 4mm OD and 2mm ID Teflon tubing
  • 1x 16T GT2 pulley
  • 1x 60T GT2 pulley
  • 1x 180mm GT2 belt
  • 1Kg of PLA filament (1.75mm black)

We still need:

  • A decent 12v Power Supply
  • Heated Bed
  • Assorted bolts, nuts, screws, threaded bar

The first few bits have already turned up….

photo_2017-02-18_16-40-30

Ideas so far are:

  1. to use a large piece of MDF sheet as a base for the 3D printer, to use wooded blocks as risers to take the two Y axis smooth rods.
  2. to finely sand to a polish the cheap, mild steel rods. Ensuring they are chamfered and oiled prior to inserting into the linear bearings.
  3. 15mm plastic pipe clips are ideal for holding the linear bearings.photo_2017-02-18_16-46-02.jpg
  4. can’t get the geared cogs built for the extruder….so will try to use some more GT2 pulleys to creat the precision and torque required.
  5. using the ready-made RAMPS is far easier and cheaper than designing, etching PCB, building and programming up my own.
  6. going to try to make most of the hot end from scratch.
  7. going to make the extruder from scratch using scrap metal/wood and making our own hobbed bolt as required. Plan to case harden it.

Every part for the Prusa i3 can be bought but doing so will likley add lots to the overall cost.

Will keep taking photos of construction and posting here should anyone like to also make their first 3D printer as cheaply as possible.

 Please also see my other progress blogs for this project by clicking here

Update On 2016 Starburst Lights

Happy New Year.

Adhering to my ‘low cost’ approach I ended up wiring the lights with a mismatch of old electrical cable and 8-core alarm cable, terminal blocks and insulating tape. All units were run using 5v from several linear regulators (7805).

I’d put my lights up early and had about two weeks before Christmas. It was around the two week time that, after some foggy and cold weather, I noticed a single, end of line pixel was remaining illuminated. I could turn the mains supply to the regulators off easily and that cleared the fault only for it to come back minutes or hours later. Finally the fault cleared completely which was strange. With the units secured into the tree with Jubilee Clips I just lived with the fault rather than get the ladder out, fiddle with them and make the fault worse.

A few days between Christmas and the New Year another star developed a faulty pixel, but this was nearer the start of its run of 10x pixels and took most of that leg out. Again I could turn the power off and back on and often it reset properly.

A few days after new year I climbed up, marked the offending positions with red tape and then took all the units down, dried them off indoors and tested again. They all work fine. I then removed some of the silicone to inspect the joins but they too look OK still.

One of the faulty units was a version where I painted all bare connections prior to the silicone sealant 2nd coat. The other was the initial black silicone/clear silicone version. I can only assume for both that water/moisture ingress caused the fault. Flexing the wire doesn’t replicate the fault so it likely wasn’t a dry joint.

The Best Bits

Having a family stop at the end of my garden one evening to say their children really liked the lights.

When up the ladder taking them down a lady slowed her car down, wound the window down and told me how much she/they had enjoyed looking at them each night.

For Next Year:

  • Add extra weather protection – perhaps a clear tubing over the top.
  • Actually spend some money on the power supplies and distribution cables/connectors.
  • Make some more units – 3+1 wasn’t enough !
  • And although I liked the unmanaged approach of self-contained units I missed being able to change what they did once they were up and running. Therefore next year I may change them into DMX512 controlled lighting. Coupled with the fantastic Vixen 3 software I could so a similar starburst, synchronise the stars, change the colours to match etc. To this end I’m already looking at testing out some RS485 comms chips from Texas instruments.

 

Christmas Fireworks

I’ve done it, I’ve actually managed to make three of those new Starburst units. They run the same code but with an additional line in each compile of the assembly to run the random number generator again.stars_tree

I’ve posted a video on Youtube here which shows the three starbursts, along with last year’s star effect (and the fact I can’t operate/edit a camera very well ! )

I hope you enjoy it.

I’m trying to make some other more basic stars to add extra colour/effect. These will be using RGB strip LED and illuminate as one single star.

I refined my build technique as they progressed and found black gloss paint was a good way to seal around the WS2812 LED PCB dies prior to mounting with clear silicone sealant…..but only the next month will prove how well that has worked.

 

 

 

Homemade PCB

It is possible to make quality PCBs at home for very little money, here is how I do it.

My first project was to make a UV exposure box. I used two under-counter slimline tubes lights and replaced the tubes with UV tubes. I built a plywood case based on a piece of glass that I had salvaged from an old document scanner. The dimensions were slightly too small and I had to make holes in the sides of the plywood case for the light power leads. I lined the inside of the case with tin foil and cut a thick piece of old card to seal the top (so I didn’t damage my eyesight).IMG_20161111_125923399_HDR.jpg

My first project was a PCB timer as can be seen on the side of the case in the photo above. It runs off 12v and energises the relay to switch power to the UV tubes.

Single Sided Board

I produce the artwork using Cadsoft’s fantastic Eagle PCB software and save it as a PDF (inverting the top layer). Next I print the artwork on a good quality laserprinter, which for me means a walk to my local library with a USB stick and spending 10p on an A4 printout. I make sure I have two images with a decent margin (say 1″) around the edge of both.

starburst_pcb

At home a pour a small amount of vegetable oil onto the paper and work it in carefully with a finger. I then press the artwork between kitchen paper in a heavy catalogue and leave it overnight to remove the excess oil. The oil makes the paper translucent to UV.

Whilst this is happening I often prep my pre-sensitised PCB by marking it out and cutting it with a fine hacksaw (usually over a waste bin to catch the dust and wear a dust mask ! ).

I cut the artwork leaving a large border if possible, lay one on the other and line up the images before stapling them together. Doubling upm the images makes for a really opaque to the UV (eg the areas we want to leave as copper).

Out of direct sunlight I remove the black protective film off the PCB and put it copper side down onto the toner side of the artwork – this way there is no microscopic gap that can cause the UV to undercut the image. This is also why the top layer/only layer is reversed.

Now let’s have some unknowns to deal with. The age of the board, type of photoresist, board temperature, tube strengths, paper thickness etc. You can do some tests on scrap pieces of board at this stage…in fact I recommend it initially rather than ruin your larger piece of PCB.

I clean the glass with a weak bleach solution and polish dry. Place the artwork (toner up and photo sensitive side down) onto the glass, place the thick card on top and then place a weight on that. I’ve used a container of fabric conditioner as I don’t know what else it would be useful for.

Now for my board variety and tube strength I find that 4 minutes is about right to soften the photoresist. When the time is up I quickly take the board and immerse it into a weak but fresh and warm solution of Sodium Hydroxide. (About 1 teaspoon into 1 L of water). This is where things may go wrong and where many people prefer to buy the proper developer solution but remember this is PCBs on a tight budget, so we’ll keep trying.

With a gloved hand, immerse the PCB into the solution and use a cheap old, soft bristled brush to wipe the copper. You should start to see the photo resist floating off where the UV light has attacked it. If the solution is too strong or hot there will be a few seconds between this happening and the rest of the photoresist being removed. If this happens that board is scrap (save it as you can coat it with photoresist yourself at a later date). If the solution is too weak or cold this can take a long time. There is also something else that can happen and that is that it looks like the photoresist has been removed but in reality there is still a very thin protective layer over the areas you want to remove the copper from….at this stage it is really hard to see if this is the case.

Once this is done I drill a hanging hole into one of the waste areas of the board and use a stainless steel brickwork wall tie/any other stainless wire to suspend the PCB into some hot Ferric Chloride solution. I heat the FeCl3 in a square Ikea vase into which I have placed an aquarium heater tube and an aquarium air pump. I also keep moving the board. I do this outside as the fumes from hot FeCl3 will seriously attach anything in the shed/kitchen and are also probably not good for health. I keep the whole lot in an old crate to catch the inevitable splashes and drips.

img_20161111_132526255

The Dirty Part – wear gloves or get yellow fingers !

I lower the board in and almost immediately take it out for a look. If the photoresist was successfully removed, those areas will be taking on a dull pink colour almost immediately. (If this isn’t the case theer may be a very thin-film of photoresist left behind in these areas. Wash the board and try dipping it in the NaOH for a bit longer/brushing while doing so). If the board was developed properly about 5 minutes in the FeCl3 and the board will be done, rinse it in a plastic bowl of fresh water to stop any chemical reactions.

Job done !

img_20161111_140601419

The SOIC PIC15F1509 for my Christmas Starburst

Double Sided Boards

I can also make these cheaply and of good quality for home projects. Using Eagle PCB software I print the top layer inverted and the bottom layer as normal. I do two images of each side and again oil the paper. When dry I cut the images out and double them up to make a better darker image. I then align the two sides and staple them together to make a ‘pocket’. After cutting the board I usually drill the hanging hole while the plastic film still protects the board from getting scratched (not as important when doing single side).

When ready I remove the photoresist protective film and place the PCB into the artwork pocket. I use a small piece of tape to secure the PCB into the pocket. I expose one side to the UV for ~4 minutes and then carefully flip the package and expose the other side.

Then develop and etch as before.

Sometime one side is really good and the other isn’t – this is a bit disappointing and often down to the developer stage rather than the etching. The edges of the board etch quicker than the centres so fine detail can sometimes be lost around the edge.

Most importantly – keep trying, make notes and perfect your technique based on what you can use cheaply.