Putting The Back On A Watch

Ever taken the back off a watch and you didn't know how to get it back on?  Ideally you'll want to find a watch press that has the correct size dies.

Watch Press

But, in a pinch, you can use a normal vice.  I have to warn you though, if you're not careful, you might end up breaking your watch.  Don't say you weren't warned.  It's not my fault if your watch ends up in 1000 different pieces.

The first step is to find a nice flat piece of metal, this is placed against the back plate.  In my case I used a large washer with a small hole in it.  You'll then need to find a stiff piece of rubber that pushes up against the front of the watch.  I found what I think was a rubber screw on foot from something like an old piece of furniture.

This all gets placed in the vice.  Make sure it is centred in the jaws as the whole point of this is to exert a gradual uniform pressure on the backplate to clip it back into place.

Watch in Vice

The next step is the one that will make you sweat and is something I can't describe.  If you've used a vice a lot you'll get a feel for how much pressure it's exerting by the resistance offered when turning the handle.  You want to gradually turn the handle while observing the watch from the side.  The gap between the backplate and the front will slowly close and then all of a sudden it will snap back into place.

Watch Compression Stack

So yeah, it'll work, but it's high risk.  You're better off going to eBay and searching for a watch press.  They cost something like $16 Australian delivered from China for a cheap one.  It'd be handy to have a die to clamp connectors together too, you know like the old db9 ribbon cable ones.

Adding a 200 Amp Range to a Multimeter With a Current Shunt

I'm working on something that requires me to measure high currents.  I don't need to be exact, I just need to know how many Amps are running through a winch so that cabling and relays can be sized.  It wasn't until this project came along that I realised I had no way to measure current over a couple of Amps.  I tried to measure the resistance of a wire and measure the voltage drop across it, but it was too clumsy and error prone.  An old automotive current meter I had should have done the job, but it seems to be dead.  The best and least frustrating solution was to do things properly and build a tool for the job.  A quick trip to Jaycar for a couple of parts and I was on my way.

Current-Shunt connected to multimeter

The set-up is really simple, it consists of a current shunt and some cabling to connect it to a load and a multimeter.  If you're unfamiliar with the concept of a current shunt here's a quick recap.  When you need to measure a current the easiest way to do it is to run the current through a resistor of known value and then measure the voltage drop across the resistor.  This resistor is called a current sense resistor or a current shunt.  Ohm's law is then used to calculate the current.  When you need to measure large currents however you need a special low value resistor.  That's where specially constructed current shunts come into play.  The one I bought is rated for 200 Amp and at this current has a voltage drop of 50mV across it.  This means it has a resistance of 250 micro Ohms (50 mV / 200 Amp).  It also means that at full current it dissipates 10 Watt, something to keep in mind.

To measure the current of a load, the shunt is inserted in series via the alligator clips and the voltage across the shunt is measured on the multimeter.  Every amp thought the shunt will cause a 250 micro volt drop across the shunt.

Current Shunt

To connect the shunt to the multimeter, the tips were cut off a cheap set of multimeter probes and eye terminals were crimped onto the leads.  You can make your own, but this way you get a nice set of moulded banana plugs on the ends of the leads.  The size of these leads doesn't matter because no current should flow through them, they are only used to measure the voltage across the current shunt.  To connect the shunt to the load you need some serious cabling.  The current I am trying to measure isn't 200 Amps, but since the shunt is rated for 200 Amp I might as well size all parts for that current in case I need it in the future.  This means that the cabling has to be quite thick.  Trying to find the cable thickness needed for this is difficult.  Everyone has a different answer, the cross sectional area also depends on the the accepted temperature rise, the insulation, and where the cables are located.  For my situation, I bought the largest crimp terminals that would fit on the shunt, and by coincidence these lugs were the exact size of some old welding cable I had.  The cable has a cross sectional area of approximately 25 square mm.  I would've preferred something a little thicker, but this should do the job adequately.

Car battery clips

It worked out nicely that the largest battery terminals from Jaycar were also rated for 200 Amps.  They also make things look a little more professional.

Battery clip teeth

One side of the teeth in the battery clip can be taken out by removing a screw.  The cable can then be crimped into it.

Teeth soldered to cable

Although the cable is crimped into the fitting, I wasn't entirely convinced it would hold, so it was soldered into place.  It's not the greatest job in the world, I don't have a soldering iron that could put out that much power, as most of the heat will be drawn down the large copper cable and dissipated into the environment.  What I do have however is a small blow torch for browning Crème brûlée that was just the right size.  It's a balancing act to get the right amount of heat into the copper and not melt the cable insulation, but I think I got the hang of it.

I've tested it by running 4 amps from a power supply though it.  The reading was close to 1 mV.  A better multimeter would make a difference, but this is precise enough to get me in the ball park.  All up I'm quite pleased with the result.  I have a useful tool that will come in handy in the future.  A pre-amplifier across the shunt would be a nice addition, kind of like a big brother to the eevblog ucurrent.

Confined Space Tool Bag/Sack

I recently had to do a bit of work under the house that required quite a few tools but found it too cumbersome to carry them individually.  It was a reasonably small space and I had to crawl quite far to get there.  I was however lucky enough to have just the right thing for the job.

The 3 foot clearance under the house

I happen to eat a fair bit of rice, and being a cheapskate, I like to buy it in bulk.  This means I'm starting to get quite a collection of the sacks that the rice comes in.  They seem too good to throw out and I use them when I can.  If I had a need for them I reckon that they would make some nice couch cushions, but in this case the bags were perfect for carrying my tools.

Ad hoc Tool Bag

Why not use a proper tool bag for the job I hear you ask.  Well, I don't do this kind of thing too often and it would just take up space I don't have, besides, I already had this on hand.

The bags even come with a handy little zip on the top to stop things falling out.  This made the job so much easier.  I was able to throw my tools in the bag and crawl to where I needed to be without too much hassle, and because everything was secure in the bag I didn't have to worry about losing things. 

Zip on the rice bag

Installing Hollow Wall Anchors With Common Tools

I recently had to install a new TV antenna point for my Grandmother and I felt the wall was too thin and weak to screw the wall plate to.  The easiest thing to do was just use some hollow wall anchors.

Wall Anchor Before Tightening

They're easy to use.  The anchor is inserted into a hole in the wall large enough for its body and then expanded until the bendable metal tabs force the fitting against the sheeting and lock it into place.

Wall Anchor After Tightening

Installing the fittings can be done a couple of different ways.  If you're going to be using a lot of them, go out and spend $30 on the correct tool for the job.  It's kind of like a pop rivet gun, except it pulls on the head of the screw to expand the tabs in the wall.  I only needed to use a couple of anchors so I decided to try a different (cheaper) method.

Insert the anchor and screw into the hole and lightly tap it into place with a hammer to push the locking teeth into the wall sheeting.

Wall Anchor In Position

The metal tabs on the back can then be expanded by tightening the screw.  There is a slight problem though, tightening the screw takes quite a lot of torque, and if you're not careful the anchor may just spin around without tightening the screw.  To prevent this, a second screwdriver is wedged against the locking teeth on the front of the fitting.

Using Screwdrivers to Tighten the Wall Anchor

With the second screwdriver against the locking teeth the screw can be tightened until the anchor is locked into place.  At this point you can remove the screw and securely attach whatever you want to the wall.  This method does require you to put a bit of force onto the screwdrivers which can be a bad idea.  Whenever forcing something with a screwdriver make sure your other hand is positioned so it wont get stabbed if the tool slips.  Be careful.

Job done.  My Grandmother has now made the switch to digital TV and is getting a good signal via a neat antenna point on the wall.  Installing anchors this way is really easy once you get the hang of it, but I'd only recommend it for the occasional fitting, for bigger jobs, get the right tool.  Besides, I'll take any reason to get a new tool (toy).

Removing Dynabolt Sleeve Anchors

While putting up the frame for my sister's chicken coop I made a slight mistake.  My attention wandered and I managed to fit a Dynabolt, or sleeve anchor as they're sometimes called, in the wrong place.  The bolt was being used to anchor a 35 mm thick pine frame to a concrete slab and once in place they're notoriously difficult to remove, so I thought I'd document how to go about doing it.  I'll refer to the bolts as Dynabolts from here on.  Although it's a brand name, it tends to be what all bolts like this are called in Australia.

First remove the nut from the bolt and tap it into the hole with a hammer until it bottoms out.  The key to removing a bolt like this is being able to get to the sleeve that surrounds the bolt.  To do this I had to remove the nuts from the surrounding anchors and lift the frame slightly.

Top Sleeve in the Frame

Dynabolt and Lower Sleeve

To understand how to remove Dynabolts it helps to understand how they work.  In the image below you can see the 4 parts of the bolt I was using.  The nut, bolt, upper and lower sleeves.  Before installation the bolt needs to be assembled by placing the lower and upper sleeves onto it and doing up the nut loosely with your fingers.  A hole is then drilled into the wood and concrete you want to join and the whole assembly is tapped into place by hammer.  The nut is then tightened with a spanner until the required torque is reached.  As the nut is tightened it draws the bolt with the flared end up into the lower sleeve and spreads it against the walls of the hole wedging it into place.

Dynabolt Parts

Trying to remove the bolt at this point is futile, the nut needs to be removed and the bolt tapped into the hole to release the pressure forcing the sleeve against the wall of the hole.  The sleeve will stay in place due to its own springiness, but it's now moveable.  I was lucky as I could still get at it.  If you can't somehow get to the sleeve you might as well cut the bolt off with a grinder.

In most cases your hole won't be deep enough for the bolt to be pushed under the level of the sleeve, this means you can't just grab the sleeve and pull it out, and pulling the bolt will just wedge the sleeve against the walls again.  The trick is to pull them both out at the same time by using a pair of vice grips to lock the sleeve onto the bolt.  This can then be pried out with a wrecking bar or similar tool.  You may need to reposition the vice grips a couple of times, but you'll get there in the end.

Prying out the Dynabolt with Vicegrips

Prying out the Dynabolt with Vicegrips

Once removed you should be able to reuse the hole.  In my case the hole was in the wrong place and the easiest option was to fill it and put the bolt in a different place.  You could probably reuse the bolt if you wanted to, but I had plenty of spare ones and didn't want to run into any problems.

The main advantage of a Dynabolt is also its biggest problem.  They are really hard to remove.  So if you make a mistake be prepared to spend a bit of time to get it out.  Take a couple of minutes to asses the situation and figure out the best course of action.  Not every application is the same, and different situations may require a slightly different method to remove the bolt.

Damaged Anchor

Securing Reinforcing Mesh When Concreting

When I started this blog I intended it to be about electronics and technical things, I also said don't hold me to that.  So today's post is a little different.  Recently my sister moved into a new house and had her heart set on keeping chickens, therefore a coop was needed.  The ones available on the market are nice but expensive, not only that, from what I can tell they're all made in China out of wood that isn't going to last long when exposed to the elements.  The best solution was to build it ourselves.  Due to this, my time for the aforementioned "technical things" has been limited, but to keep the flow of information happening here I'll write about problems encountered during the build.

The design of the chicken coop is basic, it's pretty much a 1.8 m cube, with a corrugated iron roof.  The original plan was to build it so it could be moved, but as it's in an exposed location, wind became a problem.  From what I could determine from available information, a worst case uplift force of 2 kPa could be exerted on the roof.  For a roof that's 1.8 m square, that means a lifting force of 6480 N, or 660 kg.  With this information we decided to build it on a concrete pad.  It means it's not really movable any more, but at least it'll be secure in strong winds.

I've concreted before, but it's been a while, so I wanted to use this job as practice for future projects.  We may have been able to cut some corners in places, but because I'm not an experienced concreter I did everything by the book.  To start with I levelled and compacted the site by hand, 3.5 inch wooden boxing was then constructed.  As the ground contains a lot of clay it expands and contracts depending on how wet it is.  This means that the level of the ground can change considerably, in some parts it looks like a golf course. That combined with the largish size of the block, 2 by 2 meters, reinforcing mesh was pretty much mandatory.

Concrete Formwork / Boxing with Reinforcing Mesh

The above image shows the boxing with the reinforcing mesh in place.  One piece of mesh wasn't large enough to cover the area, I had to use two and overlap them.  If you look closely you can see the three rows in the middle that were tied together with wire.  The mesh is held 40mm above the ground by plastic supports called bar chairs.  Just a note, googling "bar chairs" is not the way to find out more about them, you will however find plenty information about bar stools.  The supports aren't entirely necessary for a block this size, you could just lay half your concrete, throw the mesh in and put more concrete on top.

Placing the mesh on the supports is easy except for a small problem I came across, one corner of my mesh was slightly bent upwards.  Not too much, but enough to make it come above the level of the finished concrete.  To correct this I needed to pull it towards the ground.  Initially I planned to just put some tent pegs in the ground and wire them to the mesh, but this breaks one important rule of using reinforcing mesh.  The mesh should be completely encapsulated to prevent rust penetrating the concrete slab.  Rust could have made its way to the mesh from the external tent peg via the tie down wire.  It takes time, but it does happen.

Bar Chair Pinned to the Ground

The solution turned out to be simple.  By pinning the bar chair to the ground with tent pegs, and cable tying the mesh to it, the mesh remains isolated and completely encapsulated in the concrete.  Although it's probably not necessary on a job like this, I like to do things properly on jobs that don't matter so when it comes to jobs that are important I know what I'm doing.

After this, the concreting went smoothly and turned out pretty well if I don't say so myself.

Concrete Pad

Cheap Online Digital Microscope

A USB digital microscope that I bought from www.dx.com turned up today.  I wanted something cheap to inspect soldering and PCBs, and at $30 dollars I didn't have much to lose.

USB Microscope

The specs say the sensor is 2.0 Mega Pixels, but I can't get anything above 480x640.  Might be a driver issue, but as the included CD was blank and there is no website to download drivers the from, I'm stuck with it.  Doesn't worry me, I was fully expecting problems.  480x640 is fine for my purposes.

Microscope Specs

Package Contents

To focus the scope you manually turn a small black wheel on the side of the case.  There is also a button on the camera to take snapshots, which doesn't work.  I assume it would work if had the right drivers, but I prefer to trigger the snapshot from the computer.  This eliminates any movement of the camera that may blur the picture.  The on-off switch controls a ring 8 LEDs around the lens that are used to illuminate the subject.

It comes with a stand that is pretty much useless, which is what I had expected from reviews of similar products.

Microscope with stand

There isn't much to say, it does what I want and I'm happy with it.  As expected the product isn't great, but it gets me the results I want at a price that I'm happy to pay.

A few sample shots are shown below to get an idea of the results.  Using a ruler as a test shot I was able to determine that there are about 100 pixels per mm or 2.5 pixels per mil which agrees with the track sizing on a couple of the PCBs imaged.

It also looks as if the images are a little over exposed.  I may have to perform some adjustments there.

Surface Mount Resistor

Australian Five Dollar Note

Back of Australian 2 dollar coin

Metal Ruler with 0.5 mm Markings

Soldermask, Track, and Pads

Silkscreen

Silkscreen

Manual vacuum Pick-up Tool Attempt 1

The latest project I've been working on has been an absolute nightmare.  I've been trying to create a small manual vacuum pick-up tool for electronics work.  I have the pump and tubing all sorted, I have the tips used to pick up the parts, all I need now is a way to connect them all.

Below is the basic idea of what I'm trying to accomplish.  I have a small rubber vacuum tip from a cheap tool I bought on-line pushed onto the end of an angled dispensing tip.  The dispensing tip has a luer taper connection that needs to connect to a pen like hand held tool.

Manual vacuum pick-up tool tip

The reason I chose this design is that I can easily change tips depending on the size of the part I need to handle.  With the rubber suction tip in the image above, I can easily pick up a PCB 0.5 x 0.75 inches.  By changing the tip to something smaller like in the image below, I've been able to pick up 0603 resistors easily.  This method makes the tool reasonably flexible.

Smaller dispensing tip

As I'm unsure of what size tips I'll need, I bought a kit that has a selection of them.  Yeah, it's more expensive than buying them off a place like eBay, but once I know what sizes I'll need, I can then buy cheaper batches, but in theory I wont need too many of them.

Range of dispensing tips

Seems easy right.  Wrong.  Adapters for luer lock connections aren't that easy to come by.  You don't just go to the local hardware and buy one.  I figured the easiest way to get one was buy it from the same supplier that sold me the dispensing tips.  I choose the black fitting you can see in the image above.  It's a 1/4 inch NPT thread to a male luer lock connector.  I however didn't understand that an 1/4 inch NPT thread is actually about 1/2 an inch across.  This means that once a pipe had a thread cut in it and attached, the outside diameter of the pipe would be around 20mm in diameter, which is a little too big.  "Easy I'll just glue a plastic pipe inside the fitting" i thought.  Wrong, the fitting is polypropylene, which is super-glue resistant, which meant I had to track down a heptane primer for the plastic before applying super-glue.  Finding a suitable piece of plastic pipe wasn't easy but in a pinch you make do.

Plastic pipe from a pen case

Luckily I decided to tackle the fitting on the other end before attaching the pipe to the fitting.  All I needed was a 1/4 inch barb fitting to attach to the pipe that I'd bought.  I thought I'd go the same route as the other end and get a 1/4 inch NPT fitting and glue the pipe to the inside of it.

Fittings and altered pipe

The pipe wasn't quite the right size. To enlarge the ends I softened them with a hot air gun and then pushed them into the fitting.  The plastic walls of the pipe pushed out to created a tight fit, kind of like blow moulding.  All that was left to do was glue it all together.  That's when I found out that the barbed fitting I bought wasn't actually plastic, it was black anodised aluminium.  You might think I'm an idiot for not being able to tell the difference, but the thing was so well machined and anodised that it looked like a hard shiny plastic.  The perils of on-line shopping.

It was at this point I decided to call a halt to proceedings.  I'd made too many compromises and the design had moved too far away from my initial idea.  Getting the wrong adapter in the first place caused a chain reaction of forced choices that created a product I didn't like.  I decided to go back to the start and find an adapter I can work with.  This time around I'm getting a metal adapter that I can hopefully braze a pipe onto. If I can get the parts I'm trying to, the thing should look pretty good when I'm done.