Build a Model Lighthouse

by Michael Simpson

 

Every year I try to add a new piece to my little holiday village.  You know the kind.  They are made out of ceramic.  Some have lights and others may even have moving parts.

This year I decided to add a rotating light house.  After purchasing a rather expensive one the mechanical portion of the light failed which made the piece useless.  It also tended to glare as the light rotated.  There was also a problem with the noise. 

After returning the expensive lighthouse.  I decided to create my own.  To do this I purchased a much cheaper light house and added my own little simulated rotating light.

The keys is to ramp up the brightness of the light until it peaks then ramp it back down. 

 

Components

I decided to use the Athena for this project for a couple of reasons.  It has a built-in PWM generator that we will need to vary the voltage going to the lamp.  It uses a very simple basic type language and only costs $6.95.  

For the lamp I decided to use a bulb from one of those light stringers that contains 35 - 50 bulbs.   I purchase a whole string for about $3.  By purchasing the whole string I get plenty of other bulbs for other projects plus sockets for them.

All the components will be listed at the end of the project.

 

Hookup

First lets get our lamp setup.   You will need to cut a single lamp from the string.  All the lamps on most strings are connected in series.  Once the lamp is cut free it will look something like the on in Figure 1.

 

Figure 1

 

Figure 2

You will have to connect the loose end near the bulb as shown in Figure 2.  Please note that if you use a bulb that comes from a larger string you may have to change the duty cycle used in the hwpwm commands.

Schematic 1 shows the complete hookup.  I used a 100mw 7805 in a T92 package.  If you use another microcontroller of type of lamp you may need to use a larger regulator.

Schematic 1

Figure 3

I used the Athena Carrier 1 board as a base for the circuit shown in schematic 1.  A little hot glue to provide some strain relief for the lamp leads and the power input leads.  The circuit is simple and placement is not critical so you can use a simple perfboard if you wish.

I used a 7.5v switching AC adapter to power the board.  You can actually power several boards from a single power source.

 

Program (download it here)

dim x
dim speed

'Set up PWM signal
   hwpwm 1,255,1
   output 6

   speed = 15

loop:
   for x = 20 to 150 step 1
      hwpwm 1,255,x
      pause speed
   next

   for x = 150 to 20 step -1
      hwpwm 1,255,x
      pause speed
   next

   hwpwm 1,255,0

   for x = 20 to 150
      pause speed
   next

   goto loop
 

The program is quite simple.  After setting up the PWM port three for/next loops are executed continuously.

The first for/next loop does a ramp up on the brightness of the lamp by increasing the duty cycle of the PWM signal on port 6 of the Athena.  This simulates the lighthouse lamp moving toward you.

The second for/next loop does a ramp down on brightness of the lamp by decreasing the duty cycle of the PWM signal on port 6 of the Athena. This simulates the lighthouse lamp moving away from you.

The last for/next loop actually simulates the time the light house lamp moves away from you.

You can change the overall rotation speed by setting the speed variable to another value.

Mounting

Figure 4

The actual mounting of the lamp and the circuit board will be determined by the light house you use.  In mine I cut the original top of the light house and replaced it with a small glass candle holder. 

I created a base for the bulb by using a piece of foam board held in place with hot glue.  The bulb holder was then attached to this base and the leads run out the bottom of the lighthouse.

 

 

Parts

Easy RS232 Driver  

Athena

Athena Carrier 1

2N2222 Transistor

100 Ohm Resistor

7805 (100ma)

 

7.5V AC Adapter

9 Pin Cable

Breadboard and Wire Kit