LED ring light for Velleman K8200 3D printer

This time I would like to present you how I have added a light around the extruder.
Instead of re-inventing the wheel I just bought a simple tent light in Argos.

It contains 2 rings with white 5mm LEDs and it is battery powered. It takes 3x AA batteries so the maximum voltage is about 4.5V – close enough to onboard 5V. I’m going to drive it using PWM so I’m not worried about exceeding the limits (I’m sure there is a voltage margin in the product design so it will not catch the flames if 4.51V is provided :)

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For the PWM driver I used Atmega328P microcontroller with an Arduino bootloader. It is a bit overkill using a microcontroller for such a simple purpose but it leaves me an open window for future modifications and it was also very quick to set up from parts I had. The other big advantage of this solution comes when a small tweaks are required – it just means changing the source code and re-uploading it back to the microcontroller.
I used one of the analogue inputs (A0 - pin 23) to read value of the potentiometer and one of the PWM outputs (D10 - pin 16) to drive a transistor that controls the LEDs. Atmega328P has a 10 bit A/D converter, therefore it can read 1024 positions of the potentiometer (0-1023). However, the PWM output is only 8-bit (0-255). I have modified the range to be 3-255 – so turning the potentiometer to its edge will turn off the lights completely. I have also added averaging of last 10 readings to prevent flickering.
A 4-pin header (Reset, RxD, TxD, GND) was added for programming purposes.
As a power supply I used the main controller board, pins marked as +5V and GND from the header J1 located in the corner of the controller board.

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List of components used:

• 1x ATmega328P with Arduino bootloader
• 1x BUF644 NPN transistor
• 1x 16MHz crystal
• 2x 22p ceramic capacitor
• 1x 10k resistor
• 1x 100R resistor
• 1x 10k potentiometer

And here is the source code:

Code:

---

// Arduino program for PWM LED lighting
// Copyright 2014 - LJ Winkler (lwinkler247@gmail.com)
//
//-------------------------------------------------------------------------//
// Permission is hereby granted, free of charge, to any person            //
// obtaining a copy of this software and associated documentation files    //
// (the "Software"), to deal in the Software without restriction,          //
// including without limitation the rights to use, copy, modify, merge,    //
// publish, distribute, sublicense, and/or sell copies of the Software,    //
// and to permit persons to whom the Software is furnished to do so,      //
// subject to the following conditions:                                    //
//                                                                        //
// The above copyright notice and this permission notice shall be          //
// included in all copies or substantial portions of the Software.        //
//                                                                        //
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        //
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF      //
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  //
// IN NO EVENT SHALL THE AUTHOR OR COPYRIGHT HOLDERS BE LIABLE FOR ANY    //
// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,    //
// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE      //
// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                  //
//-------------------------------------------------------------------------//

/*
 * pin A0 - PWM pot input
 * pin 10 - PWM output
 */

const int numReadings = 10;
const int potINpin = A0;
const int pwmOUTpin = 10;
int potValue = 0;
int pwmValue = 0;
int readings[numReadings];
int index = 0;
int total = 0;
int average = 0;

void setup() {
  pinMode(pwmOUTpin, OUTPUT);
  pinMode(potINpin, INPUT);
  for (int thisReading = 0; thisReading < numReadings; thisReading++){
    readings[thisReading] = 0;
  } 
}

void loop() {
  total = total - readings[index];       
  readings[index] = analogRead(potINpin);
  total = total + readings[index];     
  index = index + 1;                 
  if (index >= numReadings){
    index = 0;                         
  }
  average = total / numReadings;       
  pwmValue = map(average, 0, 1023, 255, 0);
  if(pwmValue<3){
    pwmValue=0;
  }
  analogWrite(pwmOUTpin, pwmValue);
  delay(1);
}

---

To download the files - visit my profile on Thingiverse (http://www.thingiverse.com/ljwinkler/designs) or use direct links below:
- LED rings mount (http://www.thingiverse.com/download:455730)
- Left bracket (http://www.thingiverse.com/download:455726)
- Right bracket (http://www.thingiverse.com/download:455727)
- PWM controller board base (http://www.thingiverse.com/download:455729)
- Potentiometer holder (http://www.thingiverse.com/download:455728)
- Full clip (http://www.thingiverse.com/download:409393)
- Flat clip (http://www.thingiverse.com/download:416539)
- Pin (http://www.thingiverse.com/download:409394)


For more details, photos, schematic - please visit my blog:: http://ljwinkler.blogspot.com/2014/0...-k8200-3d.html

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Cheers,
LJ