Please Point Me in the Right Direction
By Jim Pickett - K5LAD
Keywords: LED, rotator illumination. colored LEDs
When the CDE antenna rotators were originally designed back in the 50s, I can't help thinking that illumination of the dial was almost an afterthought. Most of these units used a single 28-volt bulb running off the AC voltage being rectified and used for the metering circuit. After several months, or several years, of usage the bulb often burned out and few hams had a replacement 28-volt bulb in their junk box so the dial remained dark. As you tear more pages from your calendar, vision often declines and you reach a point where it is almost impossible to tell exactly to which position the rotor is aimed.
I've reached the point in my life where, even with a 28-volt bulb I was unable to read the dial correctly without using a strong flashlight. Something needed to be done. In truth, I had tried to build a rotor dial illuminating system out of the older bullet-shaped white LEDs but, even as small as they were, I had problems getting everything wired and arranged so that they not only lighted properly but fit correctly into the available space. I felt like I needed something better but I didn't know what that might be.
Recently I began noticing a new product on ebay, which looked interesting and seemed to be, not only very useful but a real bargain. The product was advertised as, "300 Cool White LEDs." It is made up of very small, rectangular, bright white LEDs. Each LED measures 1/8" long by 7/32" wide and were all surface-mounted, in line, on a 9/32" plastic-like material strip with an adhesive backing. The adhesive backing is covered by a paper strip to maintain the stickiness until needed. One of the neatest things is the way the designers placed the LEDs because they are mounted so that every 3 LEDs are placed with a 150-ohm surface-mounted resistor in series with the group of 3. Each group of 3 LEDs and 1 resistor has small copper circles for wiring the 12 volts to either end of the group strip. On the long strip of 300 LEDs they allowed the user to cut with a pair of scissors and isolate a single piece, again with 3 LEDs and 1 resistor. To peal off a single LED to use from the strip would be very difficult, even for a user accustomed to working with the small surface-mounted components, but by grouping them in 3s with the proper value resistor pre mounted on the strip, it becomes an easy task, even for a near novice at electronics building.
The picture below shows a strip, made up of 2 groups of the 3 LEDS, that has been cut from the original roll of 300. For every 3 LEDs you can see a collection of 4 copper-colored solder dots. The strip is plainly marked to identify where the +12 volts should go. To separate the long roll into groups of 3 LEDs, just cut the tape roll perpendicularly between the double sets of solder dots. Eagle-eyed folks can even see a small set of scissors showing where to cut.
You might think that an LED that small would not be sufficiently bright but the technology in LEDs has come a long way. Even 1 group of just 3 LEDs on 12 volts is so bright that you will not want to look at them, directly, for very long. They are many, many times brighter than the older pieces you may have used in previous LED experimenting activities.
As they come from the Chinese seller, the user can apply 12 volts DC to either end of the strip and light the whole strip tape of 300, or they can separate as many or as few LEDs as you need (always in groups of 3) and with 12 volts DC to light them up. More about purchasing these LEDs and what other similar things are available at the end of this article.
Each group of 3 LEDs covers about 2" of the mounting strip and the meter on my CDE rotor control box was about 4" wide so cutting the strip with 2 groups (6 LEDs and 2 resistors) was nearly perfect. I looked at multiple ways that I might mount the strip since I also needed to mount a diode to change the control box's metering circuit 28 volts AC and also an external dropping resistor to drop the 28 volts down to 12 volts or less. I did not consider tapping off the metering circuits' DC supply for fear that it might cause some inaccuracies in the metering circuit during a major contest.
You might note that the first conversion, with the pictures shown here, are of the control box provided with the later versions of Ham-M family, probably the Ham II or Ham III. It’s the box with 3 paddle switches for: CCW – Brake Release – CW. It uses a meter mounted so the complete top piece of the clear plastic covering over the meter face is exposed so the LED light is not blocked in any way when placed face down on the top. In a later TailTwister box conversion, there was less of the meter top showing. Its described later in the article.
The method I chose was just about as simple as could be and
uses a product found in, no doubt, every good ham's home . . . duct tape. I did not use the adhesive backing, which came
with the LED strip but simple laid the strip of LEDs face down on the top of the rotor box
meter. The top of the meter was clear plastic
and made all the LED light available to shine down on the meter face. I took pieces of the duct tape and folded into an
"L" shape with the duct tape sticky side out. Half of the "L" was on
the backside of the LED strip and the other side stuck to the backside of the control box
front panel, just above the meter. I chose to
use several pieces of duct tape rather than try to maneuver a singe piece of tape across
the full 4" meter. I was surprised, and
quite pleased, with how well this mounting system worked.
Duct tape is surely the "miracle drug" of mechanical repairs.
| I had a 330 ohm 1 watt resistor attached to one lamp lug and I had placed a piece of clear heat-shrink tubing over the lamp socket to keep anything from touching it since it was still live with the 28 volts AC. If you don't have the heat-shrink tubing, wrapping it with black electrical tape should serve the purpose just as well. If you like to take chances you can leave it bare and just be careful. Personally, I prefer the shrink tubing. This shrink tubing, obviously, doesn’t require it to be clear; any color is fine. |
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I didn't even try to calculate the size of the dropping resistor I needed but just used the 330-ohm that was already solderedon and ready. Next came the diode and I finally got a chance to use one of the completely unmarked diodes I have rolling around in my diode junk box. Probably any 50 PIV or higher diode would have worked fine but this gave me a small chance to get rid of one of those junk box unknowns (one of jillions). The diode should be of the 'power diode' category and NOT one of the small-signal diodes.
Because of the way they designed the LED strip, you can
apply the +12 volts DC to either side of the strip.
I chose to wire mine with the power wires toward the inside of the rotor box rather
than near the side of the box. That was to
make them less likely to be bumped and broken with the cover off the control box. The plus 12-volt DC wire goes to the cathode of
the diode, and the minus lead is soldered to the other unused lug on the now unused lamp
socket. (unused lug meaning the resistor
or diode is not soldered to this one)
I was prepared to add an electrolytic capacitor off the positive end of the diode to boost the voltage a bit but the first time I turned it on with the LEDs attached, I was a bit stunned at just how bright it was. The illumination of the meter face was amazing and I could easily read the numbers against the white background, even from an "up on the shelf" distance. I checked the voltage going to the LED string and it was around 7 volts. Since it was already plenty bright with the lower voltage, I had no need or desire to raise the voltage to the 12-volt figure. On a second conversion to another rotator control box, I ended up leaving off a dropping resistor completely. With the single diode, I’m only using a half-wave rectifier circuit so less than half the AC voltage is available as DC, especially with no filter capacitor. On the second conversion, with no dropping resistor, I measured the voltage feeding the 6 LEDs at 10.9 volts.
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I attempted to photograph my CDE control box with the internal LED strip installed to show how brightly it illuminated the dial. In addition, I strung a longer strip of the LEDs, fed with 12 volts to show a comparison between full voltage and the lesser amount in the box. The picture shows little difference just as viewing it "live" shows little difference. It’s plenty bright. |
I've run the boxes constantly for several days and see no difference in the brilliance in either. This project has gone over and above what I'd hoped and expected. This is not only an inexpensive project but appears to me to be a pretty ‘bright’ idea.
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The picture here shows the two converted boxes and an un-converted TailTwister control box. The picture was a bit overexposed but perhaps you can tell the big difference. The difference between a box illuminated the original way and those with the new LED conversions is as different as night and day. |
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Where To Obtain These LEDs
The rolls of LEDs from ebay come in several colors and configurations. The entire strip, with 300 surface-mounted LEDs, comes on a single plastic roll, spooled on what looks a lot like the reels we use to store 300-500 feet of Super-8 movie film (am I revealing my age?) The ones I received had a red and black wire already soldered onto one end so you can hook the whole roll up to 12 volts DC to test.
There seem to be a large number of oriental dealers selling these LED strips and the ‘first-time searcher’ can locate many of these dealers by going to www.ebay.com and entering the search term “led strips.” You’ll find quite a selection of both ebay bidding auctions and ‘Buy It Now’ offerings.
The product I used for this rotor control box project was advertised as "Cool White 5M 500CM Non-Waterproof 5050 SMD Flexible LED Strip Lights 300 leds” although I think I'd call them "Bright White." Some of the sellers also offer a full 300 LED roll of "Warm White" although they tend to be closer to a light to medium yellow color to my eye. Other popular colors for full rolls is blue, red, green. I have a roll of blue coming so I can't comment on their actual color and brilliance at this time.
Another popular roll offered is the multiple color roll. It contains LEDs colored red, blue, and green, mounted in that order, across the whole strip. The multi-colored roll includes a small plastic box which has 2 plugs to plug into 2 sockets already wired to the LED strip on the roll. The plastic box also has a coaxial input power socket to plug in a 12v DC wall wart power supply (not included). There is also an IR sensor attached to read the remote control, which was included in the purchase price. The remote control should allow the user to turn on and off various colors to mix and make other colors and display in different ways. The remote control used a different coin-type battery (#2026), which was not included, and that I haven't purchased yet, so I can't comment on the remote operation. Although I have not tried to separate my multi-colored strip LEDs, it looks like it is designed to be scissor-cut and isolated in groups of 9 colored LEDs per group. Every 9 mounted LEDs on the strip have 4 sufficient-sized oval copper tabs, which can be cut in the middle to separate into groups of 9. The tabs are labeled +, R, B, and G.
The pricing schedule is liable to be anywhere. When these products were first listed on ebay in June or July (2014), and before many folks became aware of the great use and value, the Cool White and Warm White rolls started the auction at 1 cent and the colored and multi-colored rolls started at 99 cents. Most of these are also offered with free shipping from China. Ending auction price have continued to increase, currently to the $3 plus range for Whites and $6 - $9 for the colored rolls. To give you some feel for this price increase, the first Cool White roll I bought cost me a penny with free shipping. I bid a beginning amount and no one else even bid against me so I won the bid for a penny by default. The next one was 57 cents, again with free shipping. Several others continue to go up in ending sale price, weekly. I'm thinking that they might have lost money on the first several rolls I bought from them.
I also note that these rolls are advertised as being non-waterproof while some others are advertised as being waterproofed for outdoor use. The waterproofed versions tend to be currently bringing the ebay purchase price of about double the amount, or more, of the non-waterproofed versions. I had no need for the additional protection so I have not tried to buy any of the waterproofed rolls.
I can highly recommend these LED strips to add illumination, or add increased illumination, to any meter on an existing piece of ham equipment. Since the trend, in recent years, has been for equipment manufacturers to use a strange size or style (or difficult to obtain) meter and dial illumination system, this may be a timely suggestion.
Also, if you have a dark under-cabinet situation or want to provide a well-lighted area in your garage or hamshack, these rolls of LEDs are well worth many times over their weight in gold.
