Introduction: LED Illuminated Drill Stand

Picture of LED Illuminated Drill Stand
Having started with my own home-made printed circuit boards again, I invested into a drill stand which transforms a small hand-drill into a precision drill press. But working with small details is easier when there is enough light, but how do i get it to the right place?

I constructed a 12V LED ring light with the right dimensions to mount it on the lower side of the drill stand. This instructable will show you the details.

Material:
  • 12 white 3mm LEDs
  • 4 SMD 100ohm resistors
  • circuit board
  • some wires
  • 12V power supply

Step 1: Laying Out the Circuit

Picture of Laying Out the Circuit

Based on the common design of 12V LED ribbons I decided to use segments of 3 white LEDs in series with a current limiting resistor and then use four of these sections to cover a full circle. I designed the circular PCB in the free version of Cadsoft's Eagle. In the PDF you will find a 1:1 scaled version of the layout.

Using 3mm white LEDs running at around 20mA each with a voltage drop of about 3.2V per LED gives you the value for the current limiting resistor as R=(12V-3*3.2V)/20mA or approximately 100ohm. I had to use SMD resistors because of the limited space on the circuit board, while I chose standard 3mm through-the-hole LEDs because I happen to have a large stock of these.


Step 2: Etching and Soldering

Picture of Etching and Soldering

I etched the PCB for the LED ring light using the laser toner transfer process. There are several instructables covering this topic, e.g. PCB making guide. Based on my own experience and the tip from my students, the glossy photo paper available at the Swedish chain Biltema works best.

After cutting out the circular part of the circuit board using a fretsaw I first tin-plated all copper traces. Then I mounted the four SMD resistors and finally the twelve 3mm LEDs.




Step 3: Mounting the LED Light

Picture of Mounting the LED Light

In order to attach the LED ring to the drill stand I used double-sided adhesive tape - the foam type, which is necessary to compensate for the lack of flatness of the soldered PCB. Cutting back the sticky tape with a scalpel is not as easy as it might sound, because the tape will stick to everything, including the blade itself.

Finally I could attach the lights to the drill stand and enjoy the comfort of an illuminated drill spot.

Step 4: Outlook and Improvements

Using SMD LEDs and resistors would have the advantage of offering a flat backside of the PCB which allows for easier mounting. However, the more focused light emission of the 3mm LEDs can be advantageous when it comes to the illumination of the drill spot.

Comments

orck (author)2014-08-03

I wonder why you didn't select to make a series of four leds (3V each X 4 leds =12Volts) and 3 rows in parallel. You would have the same result without having to solder the resistors.
Nice try.

uwezi (author)orck2014-08-03

Hello Orck,

you will find that it is good practice to always use resistors in combination with series-connected LEDs. This is because the exact forward volate drop of individual LEDs differs quite a bit even between LEDs of the same type and batch. Using a resistor instead of another LED gives you a much better control over the current through the invidual strings of series-connected LEDs since the resistor will "even out" these differences.

orck (author)uwezi2014-08-03

I admin that I haven't notice anything like that, but that's just me, I will never stare at the LEDs as long as my job is done.
In your current build you use the exact same resistor so...I don't get it.

uwezi (author)orck2014-08-03

You can have a look here: http://www.evilmadscientist.com/2012/resistors-for...

Or you can also look at commercial LED products like the ones I used in this instructable: https://www.instructables.com/id/Remote-controlled...

An LED has a very non-linear (actually exponential) dependence between the current which can pass and the voltage which is applied to the LED. This means if you deviate a tiny bit in the voltage you will get a big difference in the current - which in turn gives a big difference in brightness and in power and thus also heat produced in the LED. A resistor in series with the LED will "smoothen" this non-linearity: the higher current would give a larger voltage drop over the resistor which in turn will reduce the voltage which is available for the LED. In reality this will also stabilize the current for different temperatures of the LED.

However, you don't want to burn to much power in the resistor, because this will reduce the overall efficiency of your circuit. And if you use LEDs from a 3 V lithium battery you don't need a resistor, because the internal parasitic series resistance of the battery performs exactly the same task.

tbarot (author)2014-02-13

How did u tin the etched board? I had heard about liquid tin but its too expensive

uwezi (author)tbarot2014-02-13

That might actually be worth another Instructable ;-}

I use a liquid flux which I "paint" onto the board. Afterward I then track each conductor with a tinned, hot soldering iron and the flux allows the tin to nicely spread out.

By bad experience I found out that the flux I use is quite aggressive and needs to be cleaned off immediately afterwards. Letting it sit on the board over night was not a good idea.

http://www.clasohlson.com/se/Flussmedel-Ecogel/40-8226

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Bio: Native German living in Sweden
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