* The kit purchasing info can be found here:  http://www.easternvoltageresearch.com/digitalflame10.html

Last Halloween was looking for some alternatives to real candles to illuminate some Jack O'Lantern pumpkins had on the front porch of my house.  I tried some of the inexpensive LED candles that were available at some of the local retail stores, but they worked horribly - they were not very bright and the flicker algorithm wasn't even random and looked completely fake.  So to remedy this, I decided to design my own LED candle. 

The first iteration was to design an LED candle that approximated a candle flame.  I called this design the Digital Candle 1.0 and a demonstration video of this is seen here:

Note:  The video below is the low power version of this circuit.

The Digital Candle 1.0 uses four (4) 1206 based amber LEDs is in a dark room very closely approximates a single candle.  Its actually relatively bright in a dark room and great for that extra ambience - especially when camping or sitting around with your significant other for a nice romantic evening.

But in the end - i wanted more.  So i decided to create a high power variant of the original Digital Candle 1.0.  Hence, the new name - the Digital Flame 1.0.  This kit was similar in design - used the same microcontroller IC and code - but utilized high power LEDs.   I also decided to add a light detection circuit.

The light detection circuit can utilize either an onboard (provided) photo resistor, or an external photo resistor which detects the level of ambient light.  When ambient light level falls below a preset level, than the device will turn ON.  The level at which the device will turn ON can be custom set by the end user using an onboard potentiometer.  The light detection circuit can also be disabled completely and the unit operated solely with the onboard switch.

The light detection circuit was primarily added with Jack O'Lantern illumination in mind.  An external photo resistor can be used and attached through a small hole in the outside of the pumpkin, so that when its dark out, the digital candle will begin to operate without the user having to remember to turn a switch on or off. 

This design  utilizes four (4) high power PLCC-4 based LEDs and operates from two (2) AAA batteries which attach via battery clips on the rear side of the PCB board.  Both an onboard potentiometer for light detection circuit adjustment and toggle switch are provided on the topside of the board for user control.

Step 1: Features

Here are some of the features of the Digital Flame 1.0 circuit:
  • Operationg Voltage Range - ~2.5-5.0V
  • ON/OFF Switch
  • Light Detecting Photocell Circuit (Unit will turn on automatically when it becomes dark out)
  • Provisions for externally connecting a photocell sensor (onboard connector pads)
  • Operates from two (2) AAA batteries
  • Four (4) amber high power PLCC-4 LEDs
  • Advanced randomization routines simulate burning candle flame using onboard microcontroller
  • Onboard FLASH programming connections provided so you can experiment with your own microcontroller code

Step 2: Technical Information

The principle of operation is very simple.  The microcontroller generates a PWM modulated output signal which simulates the flickering of a real candle flame. 


The PWM signal is created using a linear feedback shift register (LFSR) algorithm which is used to create the randomness of the flickering.  The output PWM signal is then used to drive a high current MOSFET, Q1, which switches the four (4) LEDs, D1, D2, D3, and D4 on and off based on the PWM signal.  The light detection circuit is comprised of a P-Channel MOSFET, Q2, photo cell, R7, and Potentiometer, R9.  MOSFET, Q2, acts as a switch which turns the circuit on and off based on the state of the photocell.  Potentiometer, R9, is used to adjust the sensitivity of the light detection circuit and can also be used to disable the light detection circuit altogether.

Parts List:
  • (1) Resistor, 47k, 0805 (R1)
  • (4) Resistors, 16, 1206 (R2,R3,R4,R5)
  • (2) Resistor, 10, 0805 (R6,R8)
  • (1) Potentiometer, 1Meg, 1T (R9)
  • (1) Photocell (R7)
  • (1) Capacitor, 0.1uF, 1206 (C1)
  • (4) PLCC-4 Amber LEDs (D1,D2,D3,D4)
  • (1) N-Channel MOSFET, DMG6968U (Q1)
  • (1) P-Channel MOSFET, Si2305DS (Q2)
  • (1) Programmed Microcontroller (U1)
  • (1) Switch, Slide (SWW1)
  • (4) Battery Clips, AAA (BAT1,BAT2)

Step 3: Assembly

Assembly is very simple and straightforward.  Simply follow the attached instructions and solder parts to the PCB board.  Be sure that the LEDs and Microcontroller IC are soldered with the proper orientation. 

Step 4: Performance

The Digital Flame 1.0 circuit works extremely well and performs beyond my expectations.  I don't have a very good operational photo yet, but the photo i've included above simply does not do it justice.  This digital flame is EXTREMELY BRIGHT.  A single unit will illuminate an entire room and provide practically enough light to read from.  The light from the four (4) LEDs is definately difficult to look at without hurting your eyes.  The light detection circuit works flawlessly.  Once the proper threshold is dialed in using the onboard potentiometer, it works perfectly everytime.

As i do not have a video of this particular circuit, I do invite you to look at the low power version video of this circuit below.  The video below shows the Digital Candle 1.0 in action.   I will upload a Digital Flame 1.0 video once i get the time to finish editing it.

Note:  The video below is the low power version of this circuit.

Step 5: PCB and Kit

This circuit can be easily buitl on a breadboard or if you are handy, you can also etch your own.  For this purpose, I am offering both SOIC-8 and DIP-8 versions of pre-programmed microcontrollers which you can drop into your own designed circuits.  The pre-programmed microcontrollers can work with just a single 5mA LED or can be used to drive LARGE arrays of LEDs of many watts in power with the appropriate MOSFET output stages.

Complete Kit and details here:  http://www.easternvoltageresearch.com/digitalflame10.html
<p>Any chance you could sell one of these assembled? My solder skills need much practice. </p>
looks nice, can the flicker be controlled so its less flickery more like a candle in a draft-less environment?
Thank you. This version the flicker is not adjustable, however I'm finished up new firmware for the device which allows you to control the flicker by both an onboard potentiometer as well as a few jumpers for additional customization. <br> <br>

About This Instructable




Bio: My name is Allison and I am an engineer co-op student working for Eastern Voltage Research creating fun and exciting educational kits for students and ... More »
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