Conversion Guide: LED Markers

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Olle P


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Contents

Abstract

I've made two of these Markerlight counters:[gal_img]1338[/gal_img]... and in this article I'm going to tell you how to make your own. Although I've done a bit of research I've found no mentioning of similar devices in use by anybody before, which puzzles me. These markerlight counters look impressive but are quite easy to produce for anybody with a bit of soldering skill and miniatures building and painting experience. The downside is that the material can be a bit pricy. (Where I bought my electronic components they cost about 65 SEK (~10 USD) per counter including 25% Swedish sales tax but excluding battery.) This article will show you the details needed to buy components for your own counters. The details I willnot go into are:
  • a) Which shop to buy from, since I don't know shops worldwide (I bought my stuff from Elfa, that sells in northern Europe, and I think you might find Farnell to sell some useful LEDs as well (worldwide), Farnell's website seems pretty crappy when it comes to finding what you want though...), and
  • b) How to do the hands-on soldering job, which requires previous practice anyway.

I Target Audience

WH40k Tau players that build/paint their own miniatures and also have a bit of soldering skill. More tech savvy players just have to take a look at this picture below. (For Swedish players that want to do counters exactly like mine I have posted a very compact instruction here.) Back to Contents

II Background

(Wordy rant leading up to why my counters look the way they do. Skip to the next chapter if you're not interested.) I'm still a newbie when it comes to WH40k. It's been less than half a year since I decided to go for it, buy myself an army and start playing. Several reasons led up to my decision to play Tau, one reason being their use of markerlights.As I was planning my initial purchases I came upon an article about a Tau diorama where the vehicles have been fitted with lights. Being an engineer this got me thinking of what I could do with my miniatures... One of the very first ideas that sprung to mind was to simply put a real laser in each markerlight. Doing some research I found it to be a non-starter. Lasers are just too large and too expensive. Evolving the idea I investigated if it's feasible to put regular LEDs there instead. It's not. Even regular LEDs are too large. The only way to make the actual marker equipment send out light seems to be to place a light source (LED) inside the figure's body, and then have an optic fibre lead the light to the markerlight. That will take a lot of skill, work, money and other resources to implement. I have no plans of doing that. Wanting an easier solution I turned my attention to the markerlight counters. I realised it would be a breeze to make these shine! My initial thought was to use a small battery, one LED, a resistor and a micro-switch. Checking up on available components I soon realised that even small switches are too big, so that had to go. Next I found out that the small batteries I first opted for (16mm) will probably not last for more than a few hours, but slightly larger batteries will last much longer. Then turning to the LED. There aren't that many useful designs available, and those I wanted were only available in green. My first option was a round 3.5mm diode, which turned out to have been discontinued. Then there was a round 2mm design available in red, green and yellow. I thought these were too small though, if put alone on the counter. Then I also noticed a design with two (green) LEDs mounted in tandem in sort of a rectangular bar. I realised it would look cool to have three of these mounted in a triangular pattern on the counter, reminding me of scenes from the "Predator" movie and fairly extra terresterial. This LED design was available in two slightly different sizes, both potentially useful. Thus I had my basic design idea ready! Once I had mentally accepted the possibility to use more than one LED per counter, I figured out it could also work to use three of the 2mm type mounted in a triangular shape, but I kept that as a secondary solution. Now to the next problem: How would I actually get the parts? The chain of stores that sells those LEDs ( Elfa, with retailers throughout northern Europe) doesn't have any stores where I live. Phone order is fast and convenient (I do it quite often as part of my work), but then I would have to buy far more than I wanted to pass their minimum limit and then that price tag would be roughly doubled to cover P&P. Not an option! So I had to sit back, waiting for some sort of opportunity to arise. Fortunately I was in no hurry, since I hadn't even bought any miniatures for my army by then... Come opportunity! Soon after my design process was ready I found out (or realised) I was going to go to Stockholm for two days to attend a course, courtesy of my job. The locale had an Elfa store nearby. The course would start at 0930, and the best way to get to Stockholm at that time is a flight that arrives in Bromma airport at 0750. Thus I pre-ordered a taxi to take me (and my colleague) from Bromma not to the course but to Elfa! Since it was still possible that I wouldn't actually make it there (I could get sick, the flight be delayed, the course cancelled, etc.) I didn't dare to do a pre-order for pick-up on arrival. Instead I made a shopping list with several options for each type of item to cover for the event that something was temporarily out of stock. Come the great day... ... when I and my colleague arrived by taxi to the Elfa store, five minutes after they opened in the morning. It was a good thing I had an extensive shopping list. The rectangular LEDs I wanted were out of stock. The 2mm LEDs were available though, in all colour varieties.So which colour should I use? By this time I hadn't seen any official mentioning of any specific colour used by markerlights, so that couldn't influence my choise. Instead I thought this way: - Red is very common for lasers on Earth. T'au isn't Earth and the Tau aren't human, therefore I won't use red! - Green isn't "Earthly", but won't be very visible on the green background I will use, therefore I won't use green LEDs. - Yellow is thus the right way to go, and that's what I picked! (After leaving the store we had a nice stroll to the company where my course was held.) Today these counters, two of them, is the most completed part of my entire Tau army, in spite of the fact that it'll take a long time before I have enough units to make it worthwhile using any markerlights... Back to Contents

III The Electronics

From an electronics point of view these counters consist of; one battery, one battery holder, one resistor and one or more LEDs (Light Emitting Diodes). The battery holder simply holds the battery. In these counters it also makes up the bulk and base of the construction, which makes picking the most suitable type more interesting. The battery is a Lithium "button" type battery. Lithium batteries are 3.0V nominal voltage, which is perfect for this application. The size of battery (and corresponding holder) chosen will strike a balance between counter size and how often you'll need to replace the battery. The LEDs are the key components and also the parts most difficult to accuire. It's easy to find shops that sell LEDs, but the regular LEDs have a design we don't want to use because it will make the counters too tall! Therefore you will most probably need to find an electronics store that has a large assortment of LEDs in order to find any that fit our needs. To understand LEDs you need to know how they work: As the name implies they are diodes. Diodes generally have the characteristics that they:
  • a) Block current in one direction, known as the "rear" or "backward" direction
  • b) Let the current through in the other, "forward", direction, once a threshold, the "diode voltage" is reached. Combined with a) this means that it's important to mount diodes in the correct direction if they are powered by a DC source, such as a battery.
  • c) The voltage over the diode stays almost constant even if the current varies.
As the current increases so does the power (heat) generated in the diode. Therefore all diodes have a maximum current rating. At too high currents the diode will overheat and be destroyed. For this reason diodes need to be protected by some current limiter, which usually consists of a resistor connected in series with the diode. Light Emitting Diodes also have the property that they emit light when a current flows through them. More current results in more light, and in our application we want less light and thus put a tighter limit on the current. The resistor controls (limits) the current used. The higher the current the more light from the LEDs and the faster the battery will need replacement. Back to Contents

IV Choosing Components

IV.1 Battery Holder (and thus Battery)

For the battery holder we have two important factors: General shape and battery size. The general shape is important because it will have a huge impact on the shape of the finished counter. Fortunately one very common design is circular and flat with one connector at the edge and one near the centre. These holders are intended for mounting flat on a circuit board. This is the design I use myself as well as recommend others to use.Gallery image
This is the type I recommend. Since the design is common it's available for a broad range of battery sizes. Going strictly by looks I'd say the perfect size would be the same as, or slightly smaller than, a small figure base (25mm diametre, 4mm height). That would boil down to a holder for a 20mm battery, tops! The downside of using smaller batteries is that their capacity decreases exponentially with size, so a 20mm battery is less than half the capacity of 24mm, but more than double compared to 16mm. I use 24mm batteries (CR2430). Those should last me a full weekend tournament before needing replacement. That's in spite of the fact that I use as many as three LEDs, but partly due to the fact that I only let them glare rather than shine, feeding them only 1/6 of their rated maximum current. Back to Contents

IV.2 Light Emitting Diodes

These are obviously the most visible part of the counter. The factors that come into play are first and foremost their physical shape/design, then there are colour, light angle and current/voltage ratings, in that order.Shape/design The vast majority of LEDs are an elongated shape, shining on one end and the connector legs sticking out on the other. What we want is LEDs that can be mounted as flat as possible, shining up from the base. That means a low profile with the legs sticking out at the side(s), and there are a couple of different designs that fulfill that requirement.[gal_img]1340[/gal_img]Three useful LED designs.Colour Depending on what useful designs you have available, those might also be available in different colours. (Out of the four LED types I considered, only the least desireable came in a variety of colours, the others were all green.) The official fluff says (supposedly, I haven't read the source myself) that Tau markers use clearly visible red light, so if you want to follow that then go with red LEDs if available. (I use yellow for the reasons described under "background" above.)Light angle Most LEDs shine in a somewhat concentrated beam. For our application we want maximum spread of the light, and that can be obtained by sanding the LED surface as well as by other means. Should you have the option to choose between LEDs with different light spread, more spread is slightly better.Current rating All LEDs have a maximum current rating, usually ~20mA, and sometimes also a recommended current. This rating is useful when picking the right resistor. The more current that runs through the LED, the brighter it shines.Nominal voltage Usually in the 2.0-2.5V range. Essential knowledge when calculating what resistor to use. Back to Contents

IV.3 Rice Grain Bulbs

It has recently occurred to me that small bulbs might be a suitable alternative to LEDs. There are those that are < 2mm in diameter, and placed horisontally they'd be just the right size. They're cheaper than the relatively odd LEDs otherwise required, and also no more power consuming than LEDs, running on an even lower voltage (nominal 1.2V) and about the same current. This provides the options of using silver-oxide (1.5V) or zink-air (1.4V) batteries instead of lithium, zink-air being more expensive but also with higher energy density, allowing the use of a much smaller battery. I have absolutely no experience using grain bulbs, so some testing to see what limiting resistance to use is absolutely necessary. Back to Contents

IV.4 Resistor(s)

Here's where we need to do some maths, and if possible also some tests, to get it right. The key issue is what current to use. The problem is that you can't tell really how bright the LEDs will shine until you've tested them... I think that the LEDs should only glare a bit, since they represent reflected light rather than light sources. Then the correct current is somewhere in the 15-35% range of the rated maximum. (My LEDs are rated 30mA max, 20mA recommended. I feed them about 7mA each.)Now to the maths To compute what resistance to use we apply ohm's law:[gal_img]1341[/gal_img] Ideally you should get the LEDs before deciding what resistance to use. Then you can see for yourself how much they shine with different resistances. If you're used to soldering electronic components, then it's quite probable that you allready have an assortment of resistors anyway, so that shouldn't be a problem... The other factor to think about when it comes to resistors is how much power they can sustain. The power generated in this resistor is pretty small, typically < 50mW, so principally a resistor rated for 1/8W should suffice. However, since the resistor in our mounting will be capsuled in putty it won't dissipate the generated heat as well as it's supposed to. Therefore I'd recommend using a slightly (physically) larger resistor, rated for 1/4W or more. I have the fortune of working in a well equipped electronics work shop. Therefore I did my tests using a lab type power supply set to 3.0V and a decade resistor that let me adjust the resistance until I got it just right, and then read the set value. I tested on a single diode, and since I was to use three in parallell I just divided the resistance value from my test by three (rounding down to the nearest standard value) to find out what to use. Back to Contents

V Tools and Equipment

  • Soldering tools, to put the electronics together.
  • Plyers to cut the leads.
  • Grading tools and a knife to smoothen the surface.
  • Putty ("green stuff" or equivalent) and a small piece of adhesive tape.
  • Suggestedly some leftover sprue or some equivalent to make some feet for the counter.
  • Super glue to attach those feet. (Regular plastic glue might not work on the battery holder.)
  • Everything else you normally use to finish the bases for your miniatures.
Back to Contents

VI Putting it Together

This is not exactly how I did it, but how I will do it in the future, based on the experience gained.
  • Prep the battery holder. It's made of some "greasy" plastic and is best treated the way you'd treat a resin model.
    • Remove the plastic knobs protruding from the bottom.
    • Wash it with some grease remover. (For example washing-up detergent.)
    • Cover the hole, suggestedly using a piece of adhesive tape.
  • Soldering time.
    • Solder the LED(s) to the resistor(s) in a suitable way. Make sure the LED(s) is/are turned the right way.[gal_img]1342[/gal_img]How my counters are connected.
    • Test so that the LED(s) really do shine as you want them to.
    • Solder the parts to the battery holder. Attempt to keep it as snug as possible to the holder's surface.
  • Final touches.
    • Give it the same surface treatment as the bases of your miniatures. Add another layer or two of clear varnish to make it more durable.
    • Get a small piece of stiff sheet plastic (from a battery package or something) to use as power switch, placing it between the battery and the contact spring when the counter is not in use.
  • Back to Contents

    VII Discussion

    As you can see from reading this article it's just about impossible for me to tell you exactly how to make your own counters. First we have the limited range of useful light sources available, a range that varies depending on in which part of the world you do your shopping. Then there's the matter of personal taste and preferences regarding light configuration and intensity, counter size and battery life time. It's thus simply impossible for me to cover all combinations. With that in mind I will still try to provide some general advice below. First the most obvious and common denominators; resistors and batteries. No matter what design you choose you will need these. As a rule of thumb: The more and/or brighter light sources you want, the bigger the battery needs to be. You will also need at least one resistor per type of light source you use. With more resistors in parallell each can be smaller in size, but they will cover a larger area. I started by choosing a large battery to get plenty of power. To make that look sensible I had to use three LEDs. As it turned out I could run them at such low current that the large battery was overkill. Then we have the light source(s). From a fluff point of view the ideal would be to have one relatively bright red light and one weak greenish blue light. Greenish blue seems hopeless to get at all, but can be left out without any fuzz. Red light can be provided by an LED or possibly from a bulb. The single light source makes for a very low current, which allows for the use of a small battery holder. Using more lights is less "by the book", but can provide a cooler look. If/when I need to have more than two counters I will probably do it more according to fluff. I will see if bulbs are useful as a red light source, and if they as such are better than LEDs. Then I will make smaller counters based on 16 or 20mm batteries, with one red light on each. My current counters will then be used as pathfinder beacons or other types of markers. (This article is also available as a PDF document.) Back to ContentsI hope this article will be helpful to some readers!Olle Petersson




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