| Now
that you can Trigger your effects You have got to be able to
control the time they operate The best way to do this is with
the 555 IC timer chip There are lots of ways you can use this
timer Now you will have precise control over the length of time
your effect stays on. |
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Be
sure to use a chip holder and don't try and solder directly
to the 555 timer or you will ruin it. It's a Heat Senstitive
component like a transistor because it's full of transistors!.
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We're
going to be working with some very simple components The LED
a couple of fixed resistors an IC chip holder the 555 IC timer
chip and a capacitor Now the capacitor is polarity specific
which means you must hook it up correctly most can- type capacitors
have the negative side (or ground side) marked with some minus
signs. when you place them in the circuit, put this side towards
ground as the diagram indicates and everything will be fine.
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| Now
lets talk about the 555 chip Like a transistor - these chips
are heat sensitive So instead of soldering these chips directly
into the circuit we use an IC chip holder. THe holder is soldered
in and the chip slides right into it. Pin orientation on the
555 chip is important. You can tell which is Pin number one
by Lining up the notch to your left. Pin number one will be
just below it SOmetimes it's marked with a circular indentation |
So
much has been written about the 555 that I'm not going to
beat a dead horse by explaining it here. If you need more
info, do a search or just click these links (but come back
soon!) http://www.doctronics.co.uk/555.htm
http://www.circuitdb.com/circuits/id/107
http://www.play-hookey.com
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click
here for larger version
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Pin
number one is hooked to ground pin number three is the OUTPUT
pin of the circuit and for the time being I have hooked up the
LED and resistor to it Understand that the LED represents your
EFFECT. weather you are turning on and off a motor or turning
a props head left and right. I'll get into that a little later
in the video so for now - just remember that the LED is representing
your EFFECT. |
| This
circuit is called a one shot or monostable. When Pin the blue
wire which is hooked to pin 2 is grounded the 555 turns on the
LED (or your effect) for a specific period of time determined
by the R/C constant. You'll recall in project 2 we built a laser
trigger. It would be great to use that trigger to start the
555 one shot timer to start our effect and the let the 555 timer
control the amount of time our effect will run |
The RC constant is a way to caluculate the resistor and capacitor
values you need - for the amount of time you want the effect
to stay on. |
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Unfortunately
Our Trigger circuit provides Positive voltage as it's output
and the 555 timer circuit needs dropping voltage or 0 volts
to start it's timing. Well, in order to fix this situation -
we need to add small circuit to the output of the Trigger. It's
called an inverter.. what it does it take the positive Voltage
output of the Trigger circuit and Inverts it to negative or
0 volts. now, we can supply the proper voltage to start the
One Shot 555 timer. |
| Now
it may seem like it's getting complicated. Just think of each
circuit like it's a tool one circuit does the job of triggering
your effect the next circuit's job is to flip it's output and
the last circuit is for timing. If you think of each circuit
as a tool to do a particular task You can begin to mix and match
these 'tools' to help you accomplish what the animatronic motions
you want. |
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Let's
make that inverter You'll need a Switching Transistor NPN A
10K resistor - color code Brown - Black - Orange and a 1 K Resistor
- color code Brown - Black _Red A quick test to see if it works.
By touching the input trigger blue wire to Positive voltage
our Inverter flips that input and sends the 555 chip a dropping
voltage or 0 volts. which is whata the 555 needs to start it's
timing. Works great - now lets move on. |
| With
the 2 circuits connected together It's a good idea to test them
one more time The laser beam is broken - the CDS circuit sends
a HIGH output to the TImer circuit THe inverter flips this High
to a LOW and Starts the 555 timer Yep works like it should.
Relays are used to isolate your effect and it's source voltage
from your timing circuit. Your low voltage low current - timing
circuit charges the relay coil which physically closes the remote
contacts |
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I've added on a a pin connector to make it easier to attach
the remote trigger to this timer. Now we can locate the trigger
circuit far away from the timer and the connection can be removed
easily for setting it up. ALso with a removable trigger setup
I could use a mat switch to trigger this timer or any other
type of trigger I chose. Now you can control High current DC
motors, switch sound off and on- control other circuits. |
| Whatever
relay you choose, look on the back of the box for it's schematic.
Current flow is pretty straigtforward. Pin 3 of the 555 timer
sends a High to base of the transistor THe transistor acts as
a switch and allows current to flow to the RELAY coil the relay
coil charges up and induces the Physical contact of our EFFECT
circuit. - which is once again an LED for simplicity - |
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Click
here for 555 astable circuit |
Now you may think that we're still not getting anywhere but
we are As far as timers go - we know how to build the one shot
555 timer. We know how to trigger it and we know how to connect
a relay to it to power a high current motor. With a few simple
modifications to the one shot circuit, we can make also make
timer which does not need a trigger. Its all automatic.. As
you can see by the schematic, it's the same 555 chip - just
hooked up a little differently. This circuit will turn your
effect on and off then on and off repeating as long as you have
power to the chip. |
| Now
I control the head and neck motion of this Skeleton Prop by
using The Repeating Astable 555 timer circuit. The Head tilting
forward and remains there for 3.5 seconds, then returns upright
for 5 seconds. This adds an extra quality to the Props motion
and promotes some believability - especially if the Prop can
talk and perform other 'human' actions like eye movement, blinking
and so forth |
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This
circuit times a servo driver circuit which we're going to talk
about next. Your ability to indepentantly drive servo's with
the variety of circuits we will discuss Will really start making
your Halloween animatronics (without question-) stand out from
the crowd. |
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The Head Panning motion and the swivel motion are controlled
by individual audio tones which are inputted into audio sensing
circuits and those circuts - in turn - controll the servo driver
ciruits for each of those motions- and eventually we will go
over all these circuits as well as mechanical joint contstruction
All toll, there are 3 servos for the basic motions of this Head
of this Bucky Skeleton Prop. |
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CLICK
HERE to go to Servo Control section
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