Intro: LED Light Drawing Pens: Tools for Drawing Light Doodles
My wife Lori is an incessent doodler and I've played with long exposure photography for years. Inspired by the PikaPika light artistry group and the ease of digital cameras we took on the light drawing art form to see what we could do.
We have a large gallery of drawings on our website: LightDoodles.com. There you will also find a description of how we draw and a brief history of light drawing.
Any light source can serve as your creative implement and we shopped for every keychain flashlight, gimick pen and light wand we could find.
But we finally sat down and asked what manner of flashlight would accomadate Lori's most natural and comfortable hand posistion while drawing in mid-air. The answer was to hold the light just like a pencil with instant on/off control directly under the index finger.
Since we wanted to complete each full drawing in one exposure, she needed to be able to switch between different colored pens quickly. We also found that when drawing a large picture we needed the light to be completely exposed on all sides to minimize fading around the edges.
With these parameters, I went hunting for parts at the local electronics and hardware stores and came up with what turned out to be a simple and versatile tool that resulted in some incredible art.
Step 1: Parts List
I'll be creating a blue light pen. Attention to voltage requirements and current draw are important as different color LEDs have different ratings. Here is a list of the parts used.
Plastic Tubing - 5/8" outside diameter - 1/2" inside diameter
Plastic Tubing - 1/2" outside diameter - 3/8" inside diameter
1 Normally Open Switch
1 20 ohm Resistor - size is determined using Ohm's law
3 1.5 volt Button Batteries
Heat shrink tubing
24 gauge wire
LEDs, switch, resistors, heat shrink and electrician's tape purchased at local electronics store.
The plastic tubing was "discovered" in the hardware store. Many sizes are displayed on spools which you purchase by the foot. The 5/8" outside diameter clear tubing best fit Lori's hand. The natural curve of the tubing turned out to be ergonomic and it helps keep the pens upright and stable when placed down.
The switch is a "Normally Open" switch which means the circuit is complete and the light is on only when the button is pushed and held down. As soon as the button is released, the circuit is broken and the light goes off. Otherwise, I chose this switch for it's size and shape, not for any of it's other electrical properties.
Adding a resistor to the circuit is good practice obeying Ohm's Law.
Step 2: Warning: Math Content
I picked up the basics of LED science from the LEDs for Beginners Instructable, reading not only the Instructable itself but the many associated comments. They supply a wealth of theory and important links to everything you want to know about LEDs.
The back of the LED package provides the information we need to properly build the working circuit. Use this information to determine which type and quantity of battery and what size resistor to use.
This blue LED requires a 4.0 Forward Voltage Drop (Vf) to light.
It will pass 25 milliamps of Current (If).
Three 1.5 volt batteries in series will supply 4.5 volts.
Any combination of batteries that add up to the required voltage will do. For instance, AAA batteries are 1.5 volts and 3 in series will give you 4.5 volts.
I found these tiny 1.5 volt button batteries inside of an A23 battery (see the second picture). Three of these work nicely. See this [https://www.instructables.com/id/12-Volt-Battery-Hack!-You_ll-be-Surprised.../ 12 Volt Battery Hack Instructable] for more about that.
Obeying Ohm's Law and using this Current Limiting Resister Calculator of LEDs, a 20 ohm resistor should be placed inline in the circuit.
Step 3: Put It Together
Everything in this simple circuit is placed in series and the parts can be arranged in any order with one exception. The LED will only light if the battery polarity is correct.
Cut an appropriate length of the 5/8" OD tubing and cut a hole close to one end to accomadate the switch. Keep in mind how the pen will fit in your hand and where your finger will lie to operate the button. Since we hold this light like a pen, I place the switch where we can easily push it with the index finger.
Solder the LED, the resistor and the wires in series. Remember, the resistor can be placed anywhere in the circuit.
I place heat shrink over the exposed wires and heat the shrink with a lighter, protecting against short circuits.
Then fold the wiring up and slide inside of a 1" piece of the smaller 1/2" OD plastic tubing.
Step 4: Add the Switch
Feed the wires through the 5/8" tube, one through the hole and solder the switch inline.
Continue feeding all wires through the tube. Squeeze the switch into the cutout hole. (I bent the leads to fit.) Squeeze the 1/2" tube into the 5/8" tube.
Step 5: Add the Power Source
Finally add the batteries. This is very low-tech, but I have yet to find or build a battery holder that suits my purpose.
Strip the ends of the wires and wrap the bare wire and a small bit of aluminum foil together into a ball.
(I call myself a photographer, but I obviously need to work on my depth-of-field and flash diffusion skills.)
Use the electrical tape to hold the batteries together in series (postive terminal to negative terminal) and the wire ends in place on each end of the battery stack.
Polarity is important here. Test the light at this point and try reversing the connections if it does not work. (Remember that you have to push the switch while testing.)
Wrap a second piece of tape around the terminal ends. Stretch and wrap the tape tightly, insuring a postive connection.
Fit the battery pack into the end of the finished pen.