Introduction: Father's Day LED Tie

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A tie might not be the most original Father's day gift, but what father could resist a tie that makes him stand out from the crowd like this one:

Step 1: Things You Will Need

This is an application of the "Tiny Wearable LED Kit" that I produced for the kit challenge recently.  For details of the circuit, programing etc, please see this instructable.

In this instructable, I am going to use some thin stainless steel wire to integrate the kit into a tie for father's day.  Arguably this might be better done with conducting thread but I don't have any and the very thin wire works rather well.

You will need:

A made-up Tiny Wearable LED Kit from this instructable
12 ultra-bright blue LEDs (white, violet, UV or blue-green will also work.  Don't choose red, orange or yellow*) 
A made-made fibre tie (please don't use your dad's best silk tie - it's harder to make and he might not thank me too much)
Around 2m of thin stainless steel wire


Soldering iron & solder
M4 machine screw
Small vice grips
Heat source (blowtorch)
Heat-proof board
Small heat-proof scrap (e.g. small piece of tile)
Two small (1.5 x 2.5 cm) pieces of iron-on meding fabric  (or ordinary fabric if you are prepared to do a bit more sewing)
nail varnish
self-amalgamating tape ( optional - few cms only)

* You could probably make these work with some small resistors but that's a dozen extra parts and I haven't tried it.  See step 4 (LEDs) for speculation on resistor values.

Step 2: Make Holes for the LEDs

The reason we chose a man-made fibre tie is because we are going to cheat with making the holes.  You could make little minature button-holes and sew them all up nicely but I don't have a whole lot of spare time and with a polyester tie all you need is something round and hot.  That way we make the holes we want and seal them up so that they won't fray.

Use a rod or bolt slightly smaller than the hole that you need.  I am using 5mm LEDs so I chose a 4mm machine screw.

For this step, all we need to do is heat the end of the screw, holding it carefully so that we don't get burned.  Slip a piece of tile scrap into the tie to press against and burn your 12 holes.  Very quick and neat.

Step 3: Sewing in the Wires

Next, we want to lay down the wires for the LEDs.

The 12 LEDs are driven from only 5 pins of the ATtiny85 by taking advantage of the polar nature of an LED and the tri-state nature of the pins.  To achieve this, we have to connect the LEDs in pairs between two pins of the chip.  The LEDs of each pair have opposite polarity so we can light them independently but not simmultaneously.

As you might imagine, for five pins, we need to use a minimum of five wires.  The LEDs are each connected with one lead to one of the two "master" wires.  The other lead connects to one of three "slave" wires.  In this way we get 2 masters x 3 slaves x 2 polarities = 12 combinations.

The board is shown in the second picture.  The two "master" wires will connect to the solder points for LEDs 0 and 6, which have bold rings around them.  LEDs 0 to 5 all have one lead connected to the first master wire (from LED0).  LEDs 6 to 11 all connect to master wire 2 (from LED6).  The wiring of the first 6 LEDs is shown schematically in the third picture.

To achieve this, we first need to turn the tie inside-out.

Now we thread the stainless wire onto an ordinary sewing needle and sew one master wire all the way to the top on the LHS.  The second master wire need only go half-way up and goes closer to the LEDs than the first.  That way we need never have the LED leads cross over the master wire.

The "slave" wires go on the RHS.  The outer-most will need to go all the way up.  The middle one goes up to 2-LEDs from the top and the nearest one goes to 4 from the top.

Step 4: Add the LEDs - First 6

At this point we need to start adding in some LEDs.

I have used ultrabright blue.  You will need to pick some with a forward voltage not too far below the 3-ish volts produced by the coin cell.  If you use red or yellow they will pull so much current that it's likely you'll kill the ATtiny and in any case the voltage will be pulled down, risking a brown-out.  You could use red if you were prepared to add a resistor to each.  Somewhere around 20-30 ohms should be fine.  The current would be higher than sustainable in continuous mode but in pulsed mode it should work fine and not be tooo dim.  I will assume below that you are using white or blue and so not adding a resistor.

Starting furthest up the tie, LED0 goes with its long lead (+ve side) to master 1 (from LED position 0 on the board) and its -ve side to slave 1 (from LED position 1).  LED1 makes the same connections with the opposite polarity.

To place the LEDs, bend the legs right out flat to the plastic case and then sew into the tie with ordinary sewing thread.  Once in place, we can solder the leads to the stainless wires.  Stainless steel is a pig to solder.  I found that a flux pen, or even corrosive plumbing flux was necessary to have any hope of soldering the wires.  Even then, the best way was to make a loop out of the LED lead around the stainless wire and flood that loop with solder.

Once the first two LEDs are in, clip down the leads and move on to the next two.  Again remember that the first on (LED2) have +ve to the master side.  LED3 is the same but with -ve to the master side.

Carry on until the first 6 LEDs are in.

Step 5: LEDs - Second 6

The next 4 LEDs are the only ones where we will need to cross some of our signal wires with the LED leads.  This needs a little care and the help of a little extra fabric.  As long as we don't short the master wires to the slave wires we won't get any dangerous shorts but it will ruin the pattern if the slave wires touch each other.

As insulation, I used a couple of small pieces of iron-on patching fabric.  As you can see from the second picture, this insulates the two closest slave wires from LEDs 6 and 7, allowing them to jump over to slave 1 on the outside.  As second piece of fabric does the same so that LEDs 8 and 9 can reach slave 2 without shorting on slave 3.

You could do this without the iron-on fabric but it would take much more sewing (& a lot longer).

Step 6: Add the Control Board

You will remember that LED connection points 0, 1, 3, 5 and 6 have rings around them on the board.  This is because these are the points where you will want to connect your signal wires.  Master wires go to the bold rings on LEDs 0 and 6.  Slave wires go to the smaller rings on LEDs 1, 3 and 5.  If it's easier then 7, 9 and 11 are the same as 1, 3 and 5 respectively.  Feed the wires through, solder and clip-off.  Take care not to short any of the connections when you are trying to solder on a tiny board inside an inverted tie!

A bit or laquor with nail-varnish is a pretty good idea at this point to reduce the risk of shorting.

I also used a little self-amalgamting tape to keep the signal wires separated from each other.  Once set this becomes solid rubber and should wash OK if necessary.

Finally, turn the tie the right way out (it feels difficult but actually works quite well) and fire it up!

In the final version there are holes in the edges of the board for you to sew it into the back pocket of the tie - I will have to drill mine first.

You now have a unique, multi-mode LED illuminated tie, all ready to give to dad on father's day!

Have fun with it!