Kitchen Table Kludge

When I moved into my flat  I was offered a free table "yes please" said I thinking that I could really use some furniture.  Trouble is it was a round table, round tables are near useless in small spaces as they cannot be pushed up against a wall. Well there was an easy way to solve that...

Semi Table!

I cut the square ring beam that attaches the legs in half, ditched one of the leaves and screwed it all together. As you can tell working on the floor (no vice, no table, no chairs at that stage) and admittedly rushing does not necessarily lead to great results (most obvious of wich is probably the angle of the front most leg) But it's stable and strong and gives me extra kitchen work area without getting in the way too much. What more could you ask for really.

Long Time No Post

Hi,

I know it's been a goodly while since my last posts here but hopefully I can make up for that with a glut of post that should soon be on there way...

Mini Tables

A while ago I got a load of old Lacie hard drive enclosures, 1 or more of disks inside had died and it fell to a friend of mine to extract any good hard drives and I was offered the carcases.

mmmm...free Junk 

Looking them over I figured there was some nice aluminium and a few fans might be worth having.
Having them knocking around In my lounge the large ones instantly found use as a small  tables, so I poshed them up a bit:

Classy! (yes, that is a plater as a coaster!)

The top is some reclaimed 1x4" white wood (spruce) planed all round board wich has been stained and then varnished with some polyurethane ultra-hard varnish.

The case was sprayed with some satin black rattle-can paint (no primer, just straight down on the original paint, it seams to be gripping really well). The T slots in the edge are a challenge to paint but many light coats from multiple angles give the desired result, and they tend to be in the shade and hence not show up too badly (I thought I had got these but the camera flash shows them up pretty bad, I struggle to even see this with a torch IRL.)

Bottom View

The top is held on with some 20mm x 20mm x 1.5mm aluminium angle. I got this from screwfix (21869) wich is far cheaper than the first place I found it (home base, altho the hombase stuff did apear to be anodised unlike screwfix's plane vanilla aluminium). Not wanting to change the outside I guled the aluminium angle to the case with Araldite metal epoxy. I prepped the surface with sand paper and a stanley knife to try to give a good key. I also drilled the aluminium so that the glue extrudes though the holes kinda forming rivits. This was then allowed to cure for 24 hours to ensure a good full set on the epoxy before the wooden top is screwed down.

The top is just screwed down with ordinary wood screws, be careful not to over tighten them (I got bit keen at one point and was greeted with a loud crack, whoops!)

In it's natural Habitat.

One of the things I like about these is they are just the right size to hold a cup of tea (if you are lounging on the sofa you cant quite reach the floor with ease) and fit under the arm of the sofa (out of the way, less chance of kicking your brew across the floor!).

Joule Thief Testing

While trying to get my Joule Thief to work I brought in/wound several coils. Having these coils around I decided to try out various coil and transistor combinations to see what does and doesn't work. Maybe this will help out other people who are looking to build stuff (on the other hand maybe it won't, meh).

The Coils

From left to right:

• Big Clive Coil, 12 turns of double wound (both wires wound together, 12 turns on each) 38swg enamelled wire (e.g. YN91Y) on a small ferrite bead around 3.5mm OD, 1.5mm ID and 5mm long (N88CU in fact) on a pice of strip board for easy bread boarding.
• A common mode suppression choke (a 26-708), 37 turns of 0.5mm enamelled copper  on each side of a ferrite torroid 25mm OD, 14mm ID and 10mm long
• A salvaged ferrite (from a Lacie HDD cady) wound ala MAKE/EMS. 7 turns of 7/0.2 hookup wire on a 15mm OD, 8mm ID and 7.5mm long
• A Crude coil of 7 turns of PS2 keyboard cable on a ferrite (from a 26-8018) 27mm OD, 14mm ID and 11mm long. The PS2 keyboard cable has 4x 0.7mm wires in the middle with a foil and single wire shield. Because of the multiple cores they can be wired in two pairs (7 turns), or in series with another wire (14 turns)

Theses were paired with NPN transistors I happened to have knocking about:

The Transistors

From left to right:

• PN2222a (TO-92 case)
• BC107 (TO-18 case)
• BSS52 (TO-39 case)
• BFY 50 (TO-39 case)
• TIP31A (TO-220 esque case(may not be a 220 but a 257?))

The other components are a 1/4W (I think metal film) resister of unknown origin,  and a white LED (55-2484) the stupid brightness is probably not needed here but it's what I had to hand.

I  tried every combination of coil and transistor giving these results:

• PN2222a, all coils work well exception the common mode suppression coil wich gives a very dim light.
• BC107, all coils work and give good bright light.
• BSS52, all coils work and give good bright light.
• BFY50, all coils work and give good bright light.
• TIP31A, only works with the common mode suppression coil giving good bright light. Bupkis on and other coils.

Clearly there is some thing about the common mode coil that is ideally suited to the TIP31A but not to the PN2222a,  maybe something to do with the gate properties? The common mode coil has the most turns of wire but also probably the worst coupling (with the coils wound on oposite sides of the torrus instead of next to each other) wich is interesting, I might return to this when I have a scope.

Joule Thief

I have wanted to construct one of these ever since I first came across the circuit. A Joule Thief (if you haven't heard of it) is a 1 LED lamp that runs off a "flat" battery.

...Other battery brands are available.

Yep thats a white LED running off a "flat battery" (AAs are normally 1.5V nominal, and start about 1.7V). What makes it even more impressive is that white LEDs have a forwards voltage of around 3V, so you can't even run one straight off a fresh battery.

I first came across the Joule Thief from Big Clive (I'm not responsible for the content of external sites, some inherently risky stuff there) and then again reminded of it by MAKE/EMS.

Having been hoarding dead batteries since then and my hall having it's light switch at the oposite end to my bathroom and bed room has been all the catalyst I need to get round to it. (one too many stubbed toes/ times falling over the junk I have left in there on the way to take a leak in the night) (If the thought of a sleepy and dishevelled man going arse over apex as he's forgotten the big bag of caving gear outside his bed room door dosent make you smile, nothing will).

Circuit digram by Windel Oskay and Bre Pettis (via Evil Mad Scientist)

The transformer is a custom hand wound ferrite, and the transistor is somewhat interchangeable so I started off with a reclaimed ferrite and a BFY 50 transistor (I brought a massive (aprox. 2 cubic feet) "lucky bag" of components from a car boot sale a while back). To start with I had little luck, I tried different coils and transistors got nothing, things were getting frustrating.

Eventually I thought I was might as well go with what I know works and brought a reel of magnet wire and small ferrite beads from maplin (ala Big Clive)  as well as a pre wound ferrite  in the hope that it would have better properties. I also went over to a PN2222a that I had brought in for another project and had seen extensively in the EMS Comments. 

On my second attempt to get it working i find:

The  the current flow in the two windings needs to be  in oposite directions! (oops)

(that is to say if wrap both coils together you need the start of one coil and the end of the other connected to +V)

I must have missed this simple point the first time around. Both Big Clive and EMS point this out and it's shown in the circuit diagram by the Dot Convetion. 

Now it works pretty much (more on this later) whatever transistor or coil...DOH!

With success on the bread board I went in to production.

I had had the idea of a device that can sit on top of the battery (mostly AAs from friends caving lamps) as it is stood on end with a wire to a common ground plane almost like electric candles. 

It just so happens that AAs fit nicely into 15mm pluming fittings!

I can haz hat?

So these 15mm end caps became the base of the build. To be able to attach these (with their high thermal mass) to the circuit board I first soldered a piece of paper clip (the round end bit) bent at a right angle to give two leads to attach the board.

\m/etal end cap rocks out! 

I soldered these with a 30W iron without too much difficulty altho they do take about a miniute to reach temperature. My tesco paperclips solder really quite well, I was surprised, wonder what they are made of/plated with. 

Next on goes the board:

The cable tie and hole are used to restrain the small ferrite transformer. This picture also shows where I have broken the tracks on the strip board. 

On goes the ferrite:

How the transformer is held.

I  have black permanent markered the vero board to make it look better, why they make it in such a horrible brown I do not know. (plus black boards are all the rage)

The rest of the components just solder in, here is a no expense spent plan view.

The strange thing in top right is the unclipped LED leg wich provides a convenient attachment fot the negative lead

The transformer is wound to Big Clive's spec. using 38swg (0.15mm) enamelled wire (e.g. YN91Y) on small ferrite beads (Aprox. 3.5m OD 1.5mm ID and 5mm long) (e.g.N88CU). While fiddly you dont need to be too careful most of mine have at least a couple of crossed turns.

I used BC107 transistors as I had lots (that big "lucky bag" again) and  they are in a fairly small TO-18 packages.

This gives the final result of:

The unclipped LED leg is soldered to a 9" length of the same 38swg wire this then enters a "earthing screw terminal" (a JL99H in fact, I really like the knurled top on this terminal post, not seen them elce where)  on a plate of blank copper pcb. I initially tried 7/0.2 (aprox. 1.2mm dia.) hookup wire but it was so springy it kept knocking the battery over.

Hi-tech Candles

I'm really pleased with how this came out. About the only downside is they don't have quite enough weight to ensure a good connection particularly on slightly corroded terminals (wich ex-caving batteries often have). So I have to sand the battery terminals a bit and even then it sometimes takes a couple of goes before the run continuous.

This setup will take AA, C and D cells. AAAs are to scrawny to stand on end, this is unfortunate as I have collected quite a few, may have to make an adaptor.

I probably dont need 5 going at once (I made 7!). One is adequate to give me enough light to dodge the obstacles in the hall, but then again I have plenty of fuel at the moment:

All the Energy!

However I will doubtless be nabbing dead batteries off family and friends to feed to my vampire candles.