7a: Connecting the LED and phototransistor (or interrupter)
The photogate has a light-emitting
and a light-sensing component. The former is
a light-emitting diode (LED), which emits an infrared
beam. The sensing component is an infrared phototransistor
(PT). When the beam is broken by an object, the blockage
causes the voltage to rise across the PT, which gates
the SCR at the output of the circuit.
| For the SPG1 kit,
the PT and the LED are the individual components
shown to the right. The LED is the component
with a blue case, and the PT has a clear case.
(In an earlier version of this kit, the PT and
LED both had clear cases. If you have this version,
note that the LED has longer legs than the PT.)
For both components, one leg is shorter than the
other. The shorter leg is positive on the PT,
while on the LED, the longer leg is positive.
The wiring instructions given later in this section
will ensure that the correct polarity is maintained.
|For the SPG2 kit,
the PT and LED are housed in the two posts of
the single component, termed an interrupter, shown
to the right.
To begin wiring, use
the gray 3-conductor cable. The 4 legs of the PT and
LED (or interrupter) will be soldered to these three
Strip 1" of insulation
from each of the conductors on one end of the cable.
The PT and LED will be attached to this 1" end.
Now strip ½" of insulation from each conductor
on the other end of the cable. This ½" end will
connect with the breadboard. Strip an additional 1"
of the gray outer shielding from the ½" end so
the individual conductors can reach to their destinations.
If using individual
PT and LED components, make the following connections:
Wrap the black wire
around the shorter leg of the LED.
Wrap the white (or green) wire around the longer
leg of the PT.
Next prepare a jumper
wire that will go from the longer leg of the LED to
the shorter leg of the PT. The length of this
jumper will depend on how far apart you want to separate
the PT and LED for your photography. Strip the
wire back about an inch on each end wrap it onto the
legs of the components.
Now wrap the red wire
of the 3-conductor cable to either one of the legs
onto which you wrapped the jumper wire.
For best connections,
solder the red, black, and white (or green) wires
to the legs onto which they are wrapped. Before soldering
each leg, clip a heat sink (a metallic alligator clip
will work for this) to the leg just below the plastic
case. This will prevent the component from heating
excessively during soldering. Before starting to solder,
make sure you're working in a well-ventilated area
in order to avoid inhaling the solder fumes. A fan
to blow the fumes away from you will help. Prepare
the tip of the soldering iron by holding the solder
to it so that solder can melt and flow over the tip.
This will improve heat conductivity. Touch the
solder on the leg to which you're soldering the wire.
Hold the flat of the soldering iron tip on the leg
but not directly on the solder. As soon as the leg
is hot enough, the solder will flow. Move the solder
around so as to melt solder into the wire and onto
the leg along the length of the leg.
using an interrupter, make the following connections:
on the top view of the interrupter to the right
refer to the LED and phototransistor (PT) respectively.
The numbers refer to the legs on the underside (not
Solder the black wire
to leg 2.
Solder the white (or green) wire to leg 3.
Solder a short jumper wire between legs 1 and 4.
Solder the red wire to the jumper between legs 1and
If you have an interrupter
with short legs, you won't be able to wrap wires around
the legs. Just hold the wire to the leg and tack solder
the two parts together. Since you won't be able to
use a heat sink, minimize the amount of time that
the soldering iron is in contact with the leg.
Whether using individual
PT/LED or an interrupter, do the following:
Connect the free ends
of the 3-conductor cable to these holes:
Black to Row 2, Column
white (or green) to Row 6, Column j
Red to the positive column
Step 7b. Connecting
the flash unit
You may already have
an output cable for your flash if you prepared one
for the delay circuit. If not, use the following instructions.
The 3 feet of 2-conductor
is used to connect the output of the photogate trigger
to the PC cord of a flash unit. From one end of the
2-conductor cable, strip 1" of the gray insulation,
being careful not to cut the insulation on the red
and black wires. Then strip 1/2" of insulation
from each of the red and black wires. These
will connect to the breadboard. Next, strip
2" of the gray insulation from the other end
of the cable. Strip each of the individual wires
back 1". These will connect to the PC cord.
One way to make this connection is to cut the socket
off the end of the PC cable, strip the insulation
on the individual PC wires back by 1", splice
the red wire of the gray cable to the positive wire
of the PC cable, and splice the black wire of the
gray cable to the negative wire of the PC cord.
(The positive wire of the PC cord is usually the wire
that goes to the center pin of the PC socket.
For more information on connecting to a PC cord, see
this page: http://hiviz.com/tools/triggers/makeown.htm#connect.)
In order to connect
the flash unit to the output of the photogate, connect
the red wire to Row 13, Column b, and the black wire
to the negative column.
If you're connecting
the flash to a delay unit,
For the delayed output
(Output 2) of the delay circuit, connect the red wire
to Row 18, Column b and the black wire to the negative
column. (This is the connection shown in the photograph.)
For the undelayed output
(Output 1) of the delay circuit, connect the red wire
to Row 16, Column b and the black wire to the negative