|Time ago a friend of mine, Molly, asked me to help her to prepare some electronic effects for a costume : Boba Fett from Star Wars.|
At the time I prepared some articles to document the work.
Here the material I prepared, edited for the blog. This is the first article, others will follow.
Basically there was two areas of the costume where I helped :
The rangefinder is, in the character fiction, a device capable to identify and point a target.
Physically is a funny shaped box, with some flashing lights and a screen, mounted on the top of a rod/pole, on the side to the helmet.
When not in use it rest vertically. When in use it is lift down in front to the visor.
There are two flashing lights in front and a "screen" in the back of the rangefinder, just in front of the visor.
The lights are turned on when the rangefinder is lifted down.
The rangefinder has three lights, supposedly going on when in the horizontal position.
Two flashing lights in front and one green or white light inside, in order to simulate the light from a monitor screen .
It is possible to design different circuits capable to drive the lights.
The circuit is quite simple and "classic" and can even be minimized using special components, like this :
The circuit is extremely simple.
A 3V coin battery to power supply 3 LEDs and a tilt switch turn on the LEDs when the rangefinder is horizontal.
Two of them will be "flashing LED", i.e. LED with already included an oscillator, like this one found on AllElectronics.
Alternatively, is possible to build an astable oscillator, using a couple of transistor, so to have the LEDs flashing alternatively and not in "simil sync" as the previous circuit.
Adopting an astable oscillator is little bit more complicated and it require a PCB (a piece of sperimental board is ok).
Something like that :
The circuit seems more complicated but is really not.
Is a "classic" astable multivibrator based on two transistor NPN who drive two normal LEDs (D1 and D3).
D2 is a green or light LED.
The third way to drive the LEDs is, for my taste, the better.
Using a microcontroller, we can achieve the maximum about flexibility and an easy to program and change effects.
The hardware is very very simple, based on a MSP430F2012 microcontroller.
Simply we can connect the three LEDs to the micro I/O ports using the micro PCB.
After that is only matter to write a simple firmware capable to drive the LEDs.
It is quite easy to set up any pattern and also include some special effects on the one that simulate the screen.
The 3 LEDs will be connected to 3 I/O pin, programmed in output mode.
Another pin will be used to connect the tilt switch.
The tilt switch is not used to power supply the micro, because is not capable to give a neat on/off signal.
In this way the micro will read the tilt switch, acting also as filter.
When the tilt switch will indicate a off position, the micro will be placed in low power mode.
The rangefinder is attached to the helmet.
Since the goal is to have it moving automatically, from the vertical position to the horizontal one, a motor and gears will be needed.
The main challenge for the mechanic part, is the dimension and the torque needed to move the rangefinder.
Because the dimension, some limits will exist :
Usually is in vertical position but can be lowered in the horizontal position.
The idea is to make the Rangefinder move from vertical to horizontal, and back, automatically. The electronic to control the movement, will be based on a MSP430F2012 Texas Instrument microcontroller plus other components.
Like the lights, there are different possible choices.
The first is to use a normal DC motor, coupled with some gears.
The second, the one we adopted, uses a servocontroller.
A RF receiver will provide the input for the microcontroller (a Texas Instrument MSP430F2012), that will drive a H bridge capable to power the DC motor in both directions.
The DC motor, geared, will in the end move the rangefinder up or down.
The alternative to drive directly the motor and play with a gearbox, is to use a servo.
A "servo" is a "servomotor". Basically a "ready to use" DC motor, with a gearbox and an electronic circuit capable to drive it.
The advantage is that the motor is already handled by an electronics, easily controllable by a microcontroller.
There are many different models of "servo". They are used in the models (planes/boats/cars) and usually have a strong torque available.
Here a schematic block that illustrate what we have to do :
Wednesday, March 30, 2011
Boba Fett project
Posted by Stefano Bodini