Step 4. Adding the interrupter to the PCB

A diagram of the interrupter is shown to the right. Refer to this in order to orient the component correctly on the PCB.

Photo 4a: Turn the PCB over so that you're looking at the underside. Note the 4 numbered holes. These correspond to the numbers on the diagram to the right. Place the interrupter beside the holes in the same orientation in preparation for soldering.

Photo 4b: Insert the 4 legs of the interrupter into the board and solder on the top side of the board.

Photo 4c: A view from the side of the soldered interrupter is shown.

Photo 4d: Insert the PS2501-2 optocoupler into the 8-pin socket with the notch in the optocoupler at the same end as the notch in the socket. When seating the optocoupler, make sure to feed all eight pins into the holes. Then push down to seat the component securely.

Step 5. Drilling the lid and the bottom of the box

Photo 5a: There are 4 templates, one for the lid, and the other three for the bottom and sides of the box. Cut out the 4 templates. Then select the template for the box lid. Place the template in the under side of the project box lid. Using a hammer and a sharp, pointed instrument such as a large needle or a punch, mark the centers of the 7 holes on the template.

Photo 5b: Remove the template. Drill 3/32-in starter holes at each of the 7 locations that you marked. Then drill the holes to the sizes as marked on the drilling template.

Photo 5c: Select the template for the bottom of the box and set in place. Use your needle or punch to mark the centers fo the three holes.

Photo 5d: Remove the template and drill the three holes using the previous technique.

Step 6. Drilling the sides of the box

Photo 6a: Select the template for the long side of the box. Tape it onto the box as shown in the photo. Note the location where the side hole will be compared to the holes in the bottom.

Photo 6b: Mark the center of the 1/8-in hole, remove the template, and drill the hole.

Photo 6c: Select the template for the short side of the box. Tape it onto the box as shown in the photo. Again, note the location where the side hole will be compared to the holes in the bottom.

Photo 6d: Mark the center of the 1/4-in hole and remove the template. Drill a starter hole and then drill the 1/4-in hole.

Step 7. Completing the box

Photo 7a: Note in the photo how the two 3/8-in holes have been joined into an oval. While it's not essential to do this, it may help for seating the interrupter well. In order to join the holes, here's one technique: a) drill a 3rd 3/8-in hole between the other two, b) Use a sharp knife to cut away the excess plastic. The plastic is soft enough to be cut with a sharp knife, c) use a file to complete the oval.

Photo 7b: Remove the nut and the tab from the RCA jack. Slip the body of the jack through the 1/4-in hole in the short side of the box. Slip the tab over the threads inside the box and then screw on the nut.

Step 8. Adding the label

Photo 8a: Trim around the black border of the lid label. A stencil or razor knife with a straightedge will help to get straight cuts, but sharp scissors will also serve.

Photo 8b: Pull the backing off one of the laminate sheets, and lay the sheet, sticky side up, on a table. Carefully place the lid label, label side down, onto the sticky side of the laminate sheet. In order to avoid getting air bubbles, apply the shorter edge of the label first and gradually push it down onto the laminate with a finger.

Photo 8c: Remove the backing from the other laminate sheet and carefully apply it, sticky side down, to create a sandwich of the two laminate sheets with the label in the middle. Use the technique described above to avoid getting air bubbles. When the laminate is in place, rub a finger over the laminate and around the edges of the label to ensure a good seal. Finally, use a stencil or razor knife or sharp scissors to trim the excess laminate from around the label. The completed label with laminate applied and trimmed is shown in Photo 8c.

Photo 8d: Use a hole punch to punch out the two 1/4-in holes on the label. If you don't have a hole punch, the point of a sharp knife can be used to carve out the holes. Ragged edges will be covered later when the components are mounted.

Photo 8e: Cut the 2-in section of plastic tubing into two 1-in pieces. Align the label with the two 1/4-in holes in the top of the lid of the project box. Then push the two pieces of tubing through the holes to force alignment. Next, use a small screwdriver or a sharpened pencil to push through the 1/8-in hole in the lower right corner.

Photo 8f: Now it's time to glue the label to the top of the lid. First remove the plastic tubing and label from the lid. Then use rubber cement or other repositionable adhesive for this. Spread the adhesive over both the lid and the under side of the label (not shown). Put the label in position on the lid and use the plastic tubing and the point of a pencil or screwdriver as before to make sure that the holes are aligned. Flatten the label by rubbing a finger over it and hold in position for a minute or so to insure adhesion. Then carefully remove the plastic tubing to avoid shifting the position of the label. Any glue that extends beyond the edge of the label can be rubbed off with a finger. If there is glue smeared on the label that can't be rubbed off, use a mild solvent such as denatured or rubbing alcohol and a soft, clean cloth to clean the label. Finally, place the label under a stack of books or other weight to press it for a few hours. When completed, the lid with label should look like Photo 8f. Check the under side to see if portions of the label overlap the two 1/4-in holes. If so, use a stencil knife, razor, or knife blade to trim the label back to the boundaries of the hole. This will make it easier to insert components later.

Photo 8g: Push through the three remaining 1/8-in holes in readiness to insert the bolts.

Step 9. Adding the standoffs, switch, and LED

Photo 9a. Insert the 4 bolts through the top of the lid. Then screw the 4 standoffs to the protruding bolts on the under side of the lid.

Photos 9b,c: In Photo 9b showing the switch, notice the ring with the tab pointing toward the base of the switch. When you mount the switch on the lid of the project box, point the tab the opposite direction. Then when you insert the switch through the 1/4-in hole on the under side of the lid, the tab will slip into the 3/32-in hole, serving to prevent the switch from turning. See Photo 9c showing the switch mounted from below with the tab inserted in its hole. Now place the washer and nut on the switch on the upper side of the lid and tighen. The completed assembly is shown in Photo 9d from the upper side.

Photos 9e-g: The LED holder has two parts shown to the right. The first step in mounting the LED is to snap the collar of the LED holder into the hole from the upper side of the lid. See Photo 9e. From the under side of the lid, insert the LED into the collar as shown in Photo 9f. Note that one leg of the LED is longer than the other. Orient the LED so that the longer leg is the one nearer to the switch. Now you'll need to push the LED into the collar until the LED snaps into place. This may require quite a bit of force, depending on how tight the fit is. You can use a small, blunt instrument to push on the base of the LED until you hear it snap into place. The final part of the LED assembly is to place the ring over the collar on the under side and push it into place. When the LED is correctly seated, it will appear from the side as shown in Photo 9g.

Step 10. Wiring the box to the PCB

Photo 10a: Place the PCB onto the standoffs as shown and bolt in place.

Photos 10b,c: In order to connect wires to the legs of the LED, first strip the wires back half an inch on one end. Do this for the 2-in lengths of red and blue wire. Wrap the stripped end around a brad or small nail as shown in Photo 10b. Then you can slip out the nail and slip the spiral wrap over the leg. Place the red wire on the longer leg of the LED and the blue wire on the shorter leg as shown in Photo 10c. When you solder these connections, solder near the base of the LED and snip off the protruding legs. This minimizes the chances that the legs will touch each other when assembling the box.

Photo 10d: Strip the blue and red wires back about an eighth of an inch on the free ends. Then, bringing the stripped ends up from below, solder them into PCB holes E (red) and F (blue). Next, cut the white wire into two equal lengths of 2 inches. Strip back one end of each wire 1/4 inch. Then solder both of these stripped ends to the bottom lug of the switch as shown in Photo 10d.

Photos 10e,f: Strip the white wire from the switch 1/8 inch on the free end and solder into hole D on the PCB as shown in Photo 10e. Then strip the yellow wire back 1/8th inch on one end and solder it into hole C. Next, place the bottom of the box next to the lid as shown in Photo 10f. Strip the free end of the yellow wire 1/4 inch and solder to the center lug of the RCA jack. Finally, strip the free end of the remaining white wire 1/4 inch and solder to the side lug of the RCA jack.

Step 11. Wiring the battery holder

Photo 11a: Slip the red and black wires of the battery holder through the 1/8th-in hole on the side of the box as shown in Photo 11a.

Photos 11b,c: Strip the red wire 1/8th inch on the free end and solder it into hole A of the PCB. Strip the black wire back 1/4 inch and solder it to the center lug of the switch. Now you can stick the battery holder to the side of the box by using the two pieces of hook and loop tape. See Photo 11b. Photo 11c shows a different view.

Step 12. Completing the assembly

Photos 12a-c: Bring the lid over the box in readiness for final assembly. As you put the lid in place, feed the interrupter through the hole in the bottom of the box. Make sure not to pinch any wires between the lid and body of the box. Use the 4 black screws provided with the box to screw the lid in place. Three views of the final assembly are shown below.

Step 13. Testing and operation

Photo 13a. In order to test for proper operation, insert a fresh battery in the battery holder. Turn the switch to On. The LED should light. Now run a finger through the interrupter. The LED should blink. In fact, as long as the interrupter is blocked, the LED will be off.

Photo 13b. In order to use the photogate to observe or aid in the photography of high-speed events, connect a flash unit to the RCA jack. You'll need a cable that connects to your flash unit on one end and to the RCA jack on the other. Photo 13b shows one such cable that connects to the PC jack on the flash unit. Kits for these cables are available in the HiViz.com online store.

Photo 13c. Once the flash is connected and turned on, blocking the interrupter will discharge the flash immediately. If the event that you want to observe or photograph requires a time delay before the flash discharges, you'll need to connect a cable between the RCA jack and the input of a Delay Timer. See Photo 13c.

Caution: The Photo Gate 2i isn't designed to trigger a camera directly. While connecting your camera shutter to the RCA jack isn't likely to damage your camera and may, in fact, trigger some camera makes, we don't recommend it. The output isn't optically-isolated from the circuitry of the sound trigger. If you want to trigger a camera, connect to a Delay Timer and then connect the camera to the Shutter jack on the Delay Timer.

Photo 13d. Adjusting the sensitivity typically isn't necessary. However, some applications may require greater sensitivity. In that case, insert a jeweler's screwdriver through the hole marked Sensitivity in Photo 13d. Turning counterclockwise will increase the sensitivity. When you return the sensitivity to the original position, try to turn it about midway between the maximum and minimum positions. You'll know when you've turned too far clockwise, because the Ready LED will go out and the unit won't operate.

Additional notes on operation:

• When dropping liquid drops through the interrupter, you may wish to seal around the interrupter where it passes through the box in order to keep liquid out of the box. If you use hot glue, you can peel it off later if you need to open the box.
• The infrared beam across the interrupter is about 1/8 inch from the ends of the posts. Keep this in mind when aligning the interrupter with the beam-breaking event.