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This is a fun free-form soldering project for the holidays. It uses two flip-flop circuits to light up 16 LEDs, and you can arrange them any way you would like. This Instructable will show a (sort of) tree shape.

Free-form soldering does not use a circuit board. The components are soldered directly to each other, so the arrangement of the components becomes part of the artistic value in these circuits. There are some great and beautiful examples in some other Instructables.

Step 1: Parts

These parts are very common, are available for many sources, and are not very expensive. If you use the links below, note the shipping times - some are from vendors around the world, and the shipping time can be a few weeks. These parts are not necessarily the exact ones I used, so you may want to shop around. Also, many of the links are for a large quantity of parts - it seems like buying 10 or 100 is about the same cost sometimes since the unit price is so low on them.

For all of the resistors, 1/4 watt ones are fine.

For the Base:

For the LEDs:

  • (16) 3mm LEDs. They can be any color, and you can also use 5mm ones or any others if you want. Note that the color and size will affect the resistors you use for the LEDs - see that step for details. There are many of these to choose from - the link is to an assortment of 3 colors, and with slightly shorter leads that pictured.
  • (4) 150 ohm resistors per above
  • 6" of ~12 gauge copper - from household electrical wiring. You may want this to be shorter - some LEDs I tried had shorter leads.

Step 2: Building the Base

The base starts with a piece of copper clad board. Mine were a little less than 2" square. The base will have both positive and negative from the battery, so a groove needs to be cut along one side about 1/2" from the edge (see pictures). We only need a short side for the negative (ground) since only the transistors are soldered there. The positive side has a lot more soldering and components, so it is much wider. To make the cut, I used a file edge for some, then I tried a Dremel tool, which was fast, but sloppier for me. A hacksaw blade would probably work too. The main thing is to make sure there is no copper bridging that gap.

The order of the soldering below makes it easier to build since each part is pinned down first, then connected to other parts so you do not need to hold three things at once to solder.

The base has two separate flip-flop (astable multivibrator) circuits. There are many web sites explaining this basic circuit, so I will not repeat that here. Each flip-flop circuit drives eight LEDs (four on each transistor), so we have 16 LEDs total. Each flip-flop has two transistors, two capacitors, and two resistors (one 82K ohms, and one 100K ohms). The 82K ohm and 100K ohm resistors could all be 100K ohms, but the slight difference makes them blink a bit more naturally, so you can use ones close to those values.

Tip #1: For every connection, tin (pre-solder) the ends of both leads, then just hold them together and touch with the soldering iron. That way, you do not need to hold the solder when connecting two leads together.

Tip #2: Use needle-nose pliers to move the components and make the leads bend in the optimal positions before soldering.

Tip #3: Make sure the wires only touch where you solder them. Free-form soldering does have the issue that wires can end up touching each other. Part of the design is to arrange the wires well.

To start the base, it's easiest to put all the solder pads you need down first. See the picture for the arrangement, but you will need four pads on the negative side for the transistor emitters, four matching pads on the plus side for the timing resistors, two pads for the battery, and one pad near the middle for the copper wire tree trunk.

Next, solder the transistors to the negative side pads - the emitter lead. See the pictures for how to bend the wires first using a needle nose pliers. Remember to tin the leads first.

The timing resistors (82K and 100K) need to be cut down a bit to fit on the board. See the pictures for details on the length and how to bend them. The length is based on the size of your board, so try one first before cutting the leads. There is one of each resistor value for each flip-flop circuit.

Once the transistors and resistors are soldered to the base, you can bend them so the resistors connect to the transistor base leads - generally the middle lead of the transistor. Once they are lined up nicely, you can solder them easily.

There are two capacitors for each flip-flop. The first one will connect the closest collectors and bases of each transistor pair. Electrolytic capacitors have polarity, so make sure the negative lead on those are connected to the transistor bases (generally the center pin). So, the first capacitor will connect the closest two leads of the transistors. Bend the capacitor leads so it will fit nicely, tin the leads, solder one lead, then the other.

The second capacitor will connect the other base and collector leads - the outer two pairs, so these need to be bent a little wider, but can rest right above the first capacitors.

While soldering these, make sure all 4 transistor collectors are still accessible with the soldering iron since you will need to solder the LED strands to them.

The final step for the base is to solder the 6" piece of copper wire to the middle. Bend about a 1/4" at one end to make a good connection to the board. Make sure to tin this first and use that middle pad to solder it to. Depending on your LED lead length, you may want to shorten this wire stand a bit.

Step 3: Adding the LEDs

For each half of each flip-flop, there will be four LEDs soldered in series (in a row) with a current limiting resistor. I used 3mm red LEDs for this example, and the current limiting resistor was calculated to be about 150 ohms. This will drive them fairly brightly.

There are LED resistor calculators on the web to help you find the best current limiting resistor for your LEDs. Here is one that also has some good general info. Note that for blue or white LEDs, the 9v battery may not be enough to drive 4 LEDs. The yellow, green, and red LEDs are roughly interchangeable.

For each set of four LEDs, solder them end to end with the long wires (anodes, or +) to the short wires (cathode or -). So, start with one long lead by itself, and solder the second LED to the short end of the first LED and the long end of the second. Do that two more times to get a chain of four LEDs. Then solder the current limiting resistor to the final short end of the chain (the negative side of the circuit).

Be sure to test each set of four LEDs with a 9v battery to make sure they are working!

Once you have four chains of four LEDs each, you can solder them to the transistors. Use the resistor end of each chain of LEDs. Start with one of the inner ones to make it easier later - these will be soldered to the collectors on the transistors - generally the side opposite the emitters, and the ones with only a capacitor soldered to them. Bend the LEDs into a spiral shape up the tree, and make a small loop with needle nosed pliers at the top to hold it to the top of the tree. Then solder the next LED string, bending it around the first one. They end up in a helix shape around each other. This is an area where you can be a lot more creative. Just be sure none of the wires touch each other. As noted before, if your LEDs do not have long leads, you can always shorten the tree.

That's it! If you are lucky, it will light up on the first try. Since the LEDs were tested before, they should be OK. If only some of the LEDs light up, then you may have a capacitor backwards, or something touching or mis-soldered. If none light up, maybe there is a common mistake in there.

Have fun, and post pictures of your creations!

Step 4: Notes

I sometimes get asked how long it took to make one of these projects. The first time is always a lot longer with all the prototypes and testing! The pictures on this step show a couple of the prototypes along the way.

<p>Please post chematics, thanks :)</p>
<p>I posted a link in step two - here it is: <a href="http://free-circuitdiagrams.blogspot.com/2011/05/flip-flop-led.html" rel="nofollow">http://free-circuitdiagrams.blogspot.com/2011/05/f...</a></p><p>I used slight different values for the resistors.</p>
<p>Could You post any schematics? :)</p>

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Bio: A Maker since childhood with all the classic symptoms, a robot builder, and an Internet software CTO by day.
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