Pencils + Arduino = Bright!

Introduction: Pencils + Arduino = Bright!

Cool little arc lamp demo using the graphite in pencils and an Arduino to create DC pulses.

This low power device is very bright!

Step 1: Get Started With a Safe, Low Power Carbon Arc Lamp.

Watch the vid and read the instructable!

Safely enjoy the height of 1800's electric lighting technology.

It's your turn to be Edison, with one of the oldest electric lights! The carbon arc lamp.

This is how to make a fun carbon arc lamp demo using pencils, an Arduino and a computer power supply.

You will need:

2 pencils

1 Arduino

1 computer power supply or other DC power source (for ease of use, I'm into the ATX breakout from Dangerous Prototypes. There are many intructables on how to use discarded computers to build your own )

1 Darlington transistor or logic level Mosfet (I'm using a 2N6284G from ON Semi)

1 20 ohm 25Watt resistor

1 1000 ohm 1/4watt resistor

1 Drill press

Assorted alligator leads and wires

Step 2: The Build

The graphite "lead" in the pencil is electrically conductive. We're going to use the Arduino to turn the Darlington transistor on and off very quickly. The Darlington transistor will be connected to the computer power supply.

This will make lots of tiny sparks and prevent the pencil lead from getting too hot or from damaging the power supply.

Here's how to wire it up:

1- Sharpen the pencils and further up the body of the pencil, cut away the wood to expose the "lead"

2- Connect the computer power supply positive +12V to one of the pencil's "lead"

3- Connect one end of the 20 ohm 25 watt resistor to the other pencil's "lead"

4- Connect the other end of the 20 ohm 25 watt resistor to the collector terminal of the Darlington transistor

5- Connect the computer power supply ground to the emitter terminal of the Darlington transistor

6- Connect one end of the 1000 ohm resistor to a digital pin 6 of the Arduino

7- Connect the other end of the 1000 ohm resistor to the gate of the Darlington transistor

8- Program the Arduino using the Tone(Pin, Frequency) function:

void setup() {


void loop() {

tone(6, 31000); // this produces a 50% duty cycle square wave at 31000 Hz on pin 6


9- Clamp one pencil in the drill press chuck and one in the drill press vise

10-Power up the computer power supply and Arduino

11- Bring the two pencils together until you see sparks

12- Behold the Majesty of Carbon Arc Lighting!

13- Don't look at this directly without a welding helmet! You can damage your eyes, and get sunburn on your eyes.

(yes, it feels as bad as it sounds!)

Step 3: Explanations and Safety Tips

from wikepedia:

"An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the early 1800s, was the first practical electric light.[1] It was widely used starting in the 1870s for street and large building lighting until it was superseded by theincandescent light in the early 20th century.[1] It continued in use in more specialized applications where a high intensity point light source was needed, such as searchlights and movie projectors until after World War II."

This instructable shows you how to make a low power carbon arc lamp. The reason we are using an Arduino and Darlington is to create lots of tiny sparks. Real arc lamps use high voltage, high current DC and more conductive graphite. The graphite in pencil lead is mixed with clay to make it more or less hard. The softer the lead, the darker the writing that the pencil produces. The harder the graphite, the more clay, the less conductive it is.

The 1000 ohm resistor to protect the Arduino digital output from getting fried by too much current.

The 20 ohm 25 Watt resistor is to protect the Darlington and the power supply from getting fried by too much current.

The drill press isn't critical, but it makes it a lot easier to position the pencils at the perfect distance so the 12 Volt sparks are able to jump the gap between pencils. You must ensure that the pencil lead's are not in electrical contact with the drill press. Since the pencil body is wood, this shouldn't be a problem, but be mindful.


Even though this is a low voltage, low current, low power arc lamp it still produces powerful UV radiation and electrical noise.

The UV will damage your skin and eyes. Wear protective clothing and shield your eyes from the rays. Be sure to tell anyone around you about the dangers.

The electrical noise may affect devices nearby, be mindful.

Also the components will get hot enough to start fires and burn you, be mindful.

Have Fun!

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    6 years ago

    Thomas Edison did not invent the carbon arc lamp. The carbon arc lamp was invented by Sir Humphrey Davy before Edison was born. Thomas Edison invented the incandescent light bulb.

    Gran Abuelo
    Gran Abuelo

    6 years ago on Introduction

    Have you considered using mechanical pencil lead? It's got some clay that'll burn, but might give you a finer point.


    Reply 6 years ago on Introduction

    the 0.5mm leads that I tried used a plastic matrix, not clay. No good for heat, utter fail.

    Gran Abuelo
    Gran Abuelo

    Reply 6 years ago on Introduction

    That's a bummer. Try out multiple brands of leads I suppose?