Building the Good Enough Helix Winder (before you start)
First, choose the wire diameter, helix diameter and turns spacing you want. I use
-1.47mm wire diameter (standard 1.5mm² electric wire in europe). Actually I measured it to 1.41mm... cost saving thing I guess.
-8mm turns spacing
-8mm helix diameter
For this tutorial, I will pretend to use 24mm turns spacing so you don't get too confused.
Note that the helix is shown as a triangular wave (but actually is a sin wave). Also note that I take dimensions *inside* the copper wire, not at center of the wire.
Your aluminium tube diameter must be equal to Helix diameter (8mm), and you piece of wood thickness must be equal to Turn Spacing (24mm, but if you want 45° helix, use 8mm also)
Building the Good Enough Helix Winder (glue the front plate)
On one piece of wood, cut two grooves on one side, spaced by about 20-30mm (1 inch). Mark perpendicular lines on the face, then apply glue on the wood side but not in the area between the two grooves.
Clamp a second piece of wood on the first one. Cheap clamps will be good enough, but make sure that you press strong enough (excess glue should come out) and that the two pieces of wood are perfectly flush (if they are not, sand one side flat after gluing).
The groove prevents the glue from reaching the central area. Wipe the glue that comes out of the joint before it is dry (or sand it later)
Building the Good Enough Helix Winder (glue the main block)
Cut two small pieces of wood (approximately square) and glue them between larger ones as shown.
The block does not need to be hollow, this just saves wood. All you want is a block that is at least 25mm (1") thick so the tube can be held perpendicular to the block. Glue on the side that are really square, not the one you sawed.
Building the Good Enough Helix Winder (Drilling holes)
Using a drill press, drill a hole in the center of the main block. Diameter should be just above the helix diameter. With a 8mm helix diameter, drilling a 8.1mm hole. If you don't have a 8.1mm hole, drill a 8mm hole then sand to be sure that your 8mm aluminium tube slide freely in the hole but is kept steadily perpendicular to the block.
Using a nail, make a small hole just above the center of the front plate. I use 1.4mm wire, so I will mark a point about 0.75 mm above the joint. (formula is wireDiameter/2/cos(helixAngle) , but you need to make it slightly shorter because wood will be strained by the wire)
Then, using you drill press, drill a 8.1mm hole using the nail hole as a guide. This is the part the requires the more precision.
Building the Good Enough Helix Winder (Glue the plate)
Cut the marked center part of the front piece (remember : there is no glue in this areau, so just cut down to the middle)
Cut a piece of aluminium tube about 300mm long. Put it through the the holes in the block, and use it as a guide to position the face plate on the block. Spread glue between the block and the face plate, clamp, then remove the tube to make sure it does not get glued.
The half-hole in the plate must touch the tube as much as possible, but should not prevent the tube from moving freely in the holes.
Here is how it should look like:
And from the back side:
Two more holes and you are done!
Building the Good Enough Helix Winder (Drilling the wire-feeding holes)
Now is time for a bit of calculation. I choose a helix diameter of 8mm, and turn spacing of 24 mm. The angle between wire and helix axis will be :
If you used 8mm for both value, you should find 45° angle. With 8m and 24mm you would find:
asin(9.5/25.5) = 21.87...°
Set your drill press to 22°, and drill two holes slightly larger than your wire diameter (in my case, 1.4mm wire and 1.5mm drill bit) at the positions shown on this picture:
The holes should be tangent to the tube's hole. They should also be drill in the block only and be tangent to the border of the face plate. Left on the picture is wrong, right one is almost good. This is what happen when you do not mark the center of the hole with a nail before drilling........... :(
Building the Good Enough Helix Winder (test the GEHW)
Insert some wire in one of the small holes (depending on the helix direction you want), wrap it around half of the tube so it comes out just at the corner formed by the tube and the face plate:
Grab the wire between the tube and your thumb, and with the other hand just turn the block. Let the winder move on the aluminium tube as you wind, but make sure that the wire stays in contact with the face plate to keep a constant spacing.
On my first test, I made three helix, and put them side by side. The larger difference in turns size I could find was 0.2mm. Here are two of them, ready to be part of the first DNA lamp:
Good enough :)
Determine tension and intensity for each led
Note : this step is optional, if you think that your resistors are close enough to mine, you can just use the value I found while writing this tutorial.
If you use a 9V PSU, find 4 10kR potentiometers. If you'll use a 5V one, 2.2kR is better. (0.5W is enough with 9V PSU, 0.1W with 5V, even cheap SMD will be fine). If you don't have four potentiometers, do as I did: try different resistor.
Power on led of each color via one potentiometer or resistor as this:
If you want a clean an easy way to put 0603 leds on breadboard, see my other tutorial here.
Start with potentiometers on the higher value (10kR or 2.2kR), and slowly rise the luminosity (decrease resistance) until you think it looks good (you do not want a blinding led, remember that you will have 12 leds and some people take a close look)
Find positions for the potentiometers that give even luminosity: you do not want some colors to be brighter than others.
Then, using your voltmeter, note the tension for each led and each potentiomer. When done, remove the PSU and measure the resistor value for each potentiometer. Then calculate intensity using the formula:
Where U is the tension measure at the potentiometer in Volt, and R the potentiometer value in Ohm. Result in Amper
(Alternatively, you measure intensity and tension for each leds).
Here are the values I found, yours should be close:
Red: 1.88V, 7.5mA
Green: 2.95V, 3.4mA
Blue: 2.74V, 2.0mA
Yellow: 1.96V, 8.9mA
Choose your color pairs
We will use one color for each nucleobase. Remember that nucleobases go in pairs, and that the only possible pairs are adenine-tymine and guanine-cytosine, so if you don't want your bio-engineer friend to make sarcastic comments about your DNA Lamp, always use the same two pairs of different colors.
You can have either:
-mix of red-blue, blue-ed, yellow-green and green-yellow (I choose this one)
-mix of red-green, green-red, blue-yellow and yellow-blue
-mix of green-blue, blue-green, red-yellow and yellow-red
But you can't have:
-red-green and red-blue pairs
Calculate resistors value
Here is a simplified schematic of how each row of two leds will be built:
Here, L1 is the led that will require more intensity, and L2 the one which requires less. e.g., if you want a row of red and blue leds, L1 is red (7.5mA), L2 is blue (3.8mA).
I will not detail calculations too much, do it as an exercise if you please. Important results are :
Rc = (Upsu - Ul1 - Ul2) / Il1
Rl2 = Ul2 / (Il1 - Il2)
-Rc and Rl2 are the values of the resistances in Ohm
-Upsu is the tension of your power supply in volt
-Ul1 and Ul2 are the tensions of the leds (measured at previous step, Volt)
-Il1 and Il2 are the intensity measured or calculated at previous step. Warning: value is in Ampers, not milliAmpers.
As an example, with a red and a blue led, with a 9V PSU and led characteristics I measured in previous step:
Rc = (9-1.88-2.74) / 0.075 = 584 Ohm
Rl2 = 2.74 / ( 0.0075 - 0.002) = 498 Ohm
Side note: You may think that I could have used a 5V psu to save power and money (cheap cellphone chargers and USB ports deliver 5V). The problem is that the cheap PSU are not realy precise. My phone charger delivers 5.5V when not used, my regulated PC usb port delivers precisely 5V. With 5V I would need Rc = 51 Ohm. With 5.5 provided under low charge by the USB wall adapter, I would need Rc = 117 Ohm. That means that if I plug the "5V" DNA lamp on my wall charger, leds would get twice the intended intensity. Still not armfull (leds should accept 15-20mA), but then intensity and luminosity would not be matched between leds. A 0.5V difference on the 9V version of the lamp would only give a 11% difference in intensity. You would barely see it. Also, using 9V allows me to have blue and green rows. So let's buy that crap $3 9V wall adapter on ebay and go on.