Thursday, August 18, 2022


**Updates Log**

9/27/22 code updated for millis() rollover

2/3/23 parts list included

 So I’m, really happy about this new board I had made.

It uses a Arduino Nano to control PWM signals for six different channels of lights. There are two potentiometers, one to select the effect, and a second to change the speed of that effect. The board uses IRLB8721 mosfets to control current to the lights. According to Adafruit these mosfets are capable of switching 15A of current so each channel could run several lights in parallel.

These are the lights I use. They were suggested by another haunter, because they are waterproof, they fit inside a PVC fitting, and draw only 60mA at 12V DC. To find them you can search Eagle Eye LED 18mm on Amazon/EBay/AliExpress.

Here’s a 4 minute demo of the board in the lab:

There are 4 different effects:

1. Solid - all lights are on and dimmable by the speed potentiometer

2. Firelight - a low flicker meant to evoke the light of a fire. Works well with several amber on the same channel and 1 dim red on another channel

3. Wavey - All channels slowly pulse on and off at slightly different wavelengths so they don’t synchronize. Speed potentiometer controls how fast they pulse

4. Lightning  - Each channel strobes on with a random delay and a random number of flashes. Speed potentiometer controls how frequent the flashes are. 

**I'm not in the business of selling Halloween circuit boards, but I usually have to order more than I need for any given project. If you're into DIY electronics (and let's face it, you wouldn't be reading this otherwise), and want one of my boards, send me a PM.** 

Here's the Fritzing:

The schematic:

Here's the code for the nano: (updated 9-27-22 to fix millis() rollover.)

// Jekyll-Labs Lightboard v1.0
//  D2 sensor
//  D3 Power MOSFET (PWM avail)
//  D4 sensor
//  D5 Power MOSFET (PWM avail)
//  D6 Power MOSFET (PWM avail)
//  D7 Unused
//  D8 Unused
//  D9 Power MOSFET (PWM avail)
//  D10 Power MOSFET (PWM avail)
//  D11 Power MOSFET (PWM avail)
//  D12 unused
//  D13 unused
//  A0/D14 Unused
//  A1/D15 10k potentiometer
//  A2/D16 10k potentiometer
//  A3/D17 Unused
//  A4/D18 Unused
//  A5/D19 Unused
//  A6/D20 Unused
//  A7/D21 Unused

int ledpin[] = {3, 5, 6, 9, 10, 11};
int effectpin = A1;
int freqpin = A2;
int effect = 0;
int freq = 0;
int brightness[6];
int oldbrightness[6];
int fldelay = 75; // fire light flicker delay
int flalpha = 20; // fire light alpha 0-100 (low values less dynamic changes)
unsigned long  lastupdate[6];
int between=500;
int randwavel[6];
int wavelength[6];

void setup() {
  for (int i =0; i<=5; i++) {
  for (int i =0; i<=5; i++) {            //setting variables for flicker
    brightness[i]= random(256);
    oldbrightness[i] = brightness[i];
    randwavel[i] = random(500);

void firelight(){
  for (int i =0; i<=5; i++) {
    if ((millis()-lastupdate[i])>fldelay) {
      lastupdate[i] = millis();
      brightness[i] = random(255);
      brightness[i] = (flalpha * brightness[i] + (100 - flalpha)*oldbrightness[i])/100; 
      oldbrightness[i] = brightness[i];

void wavey(){
  for (int i =0; i<=5; i++) {
    wavelength[i] = (freq/100)*1500 +1000 + randwavel[i];
    int remainder = millis() % wavelength[i];
    if (remainder <wavelength[i]/2){
      brightness[i] = map(remainder, 0, wavelength[i]/2,-128,384);
      if (brightness[i]<0) brightness[i]=0;
      if (brightness[i]>255) brightness[i]=255;
    if (remainder >=wavelength[i]/2) {
      brightness[i] = map(remainder,wavelength[i]/2,wavelength[i],384,-128);
      if (brightness[i]<0) brightness[i]=0;
      if (brightness[i]>255) brightness[i]=255;

void solid(){
  freq = map(freq,100,923,0,255);
  if (freq<0) freq=0;
  if (freq>255) freq=255;
  for (int i =0; i<=5; i++) {

void lightning(){
  for (int i =0; i<=5; i++) {
    if ((millis() - lastupdate[i])> between) {
      for (int c=0; c< random(7); c++){ 
        digitalWrite(ledpin[i], HIGH); 
        digitalWrite(ledpin[i], LOW); 
      int lidelay = map(freq,0,1023,3000,20000);
      between = 500+ random(lidelay);
      lastupdate[i] = millis();

void loop() {
  freq = analogRead(freqpin);
  effect = analogRead(effectpin);
  if (effect<100) solid();
  if ((effect>=100)&(effect<512)) firelight();
  if ((effect>=512)&(effect<923)) wavey();
  if (effect>=923) lightning();

Parts List and links

Where convenient, I’m including links to parts on Digi-Key. I do not receive any commission from Digi-Key (or the parts fabricators), and I can’t vouch for the specific parts I link to. But I generally find Digi-Key to be very reliable with a good library of parts. You may find cheaper prices elsewhere.

1- Arduino nano
    Or suitable clone

2- 15 pin female headers
    Also can use a long strip of female headers and cut to fit

6 - N Channel Mosfets
    I like the IRLB8721PBF mosfet, but any logic level mosfet with enough volts should work. FQP30N06L is also a solid choice. 

2 - 10k Potentiometers
    Rather expensive here. There are cheaper ones elsewhere, but quality may be an issue.

7 - 2 channel 5.08mm pitch phoenix screw headers
    Any 5.08mm (0.2”) pitch screw terminal will work, but I really like the mechanism on the Phoenix product. 

Wednesday, August 17, 2022

Fake Electric Zap (capacitive touch)

Another Haunter on Facebook asked about making a barb wire fence that would make an "electric shock" noise when you touched it. That inspired me to put together a quick prop based on capacitive touch.

It’s pretty simple to put together. No Arduino involved. The sound comes from an Adafruit Sound FX board. They aren’t the cheapest option, but really easy to work with. I've saved a sound clip of electric shock to the board's memory as T01HOLDL.wav. This way it will play the sound whenever pin #1 is connected to ground. WAV files require less decoding so play faster. Pin #1 is hooked to the output from a capacitive touch sensor. The sensor is set to give a ground signal when you touch it, 5v when you don’t touch it. For this particular sensor, you need to add a glob of solder to connect the "A" pads.  I then scratched off some of the plastic covering the sensor and soldered a long wire to the sensor. That’s then connected to the outlet (which is of course NOT connected to household power or anything else.) 5V DC power from a wall wart transformer (or even 3 AA batteries) run to the power pins for both the sound board and touch sensor.

I highly recommend the Adafruit tutorial on their SoundFX boards. There are cheaper options for audio (DFPlayer mini is one of my favorites) but Adafruit is a great place to start. Adafruit also sells a great Capacitive Touch sensor board, but this one is cheaper and has the option to output ground signal with touch.