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Assembly and Operating Instructions for Kits


Crossed-Beam Photogate Frame and Cable Assembly


Assembly instructions for other kits


The following list of instructions is intended to supplement the video tutorial provided here.

Cutting and drilling the frame
Assembling the frame

Adding the emitters, detectors, and detector shields

Wiring the emitters and detectors

Adding the plug to the 3-conductor cable


Cutting and drilling the frame


Tools needed: Saw (mitre box recommended for straight cuts), small round file, drill motor (drill press recommended), 13/64" and 1/4" bits or metric equivalents


Materials needed: 2- to 4-ft of 1/2-in PVC pipe (depending on the size frame you wish to make), 4 1/2-in PVC elbows, 12-15" length of 3/16" wood or steel dowel rod


Skip to Assembling the Frame if you have a frame kit.

  1. First decide what size frame you'll need based on the size of the subjects that you'll be photographing. For example, a 6-in frame would be sufficient for many insects. For small birds, 10 inches works well. The largest frame size that we've successfully tested is 12 inches. Note that the larger the frame, the more delicate the sensitivity adjustment is.

  2. Cut 4 sections of 1/2-in PVC pipe to the length that you decided on in step 1.
  3. Mark the center of each section of cut pipe. Then drill a 13/64-in hole completely through each section at the midpoint. See the figure below.

  1. In each section of pipe, use a 1/4-in drill bit to widen the hole on one side only of the pipe.

  1. File the holes and ends of the pipe sections as needed to remove shavings.



Assembling the frame

  1. Lay the four sections of pipe and four 1/2-in PVC elbows on a table as shown below. Make sure that the larger of the two holes in each section of pipe is on the outer side of the square.

  1. Push the sections into the elbows but not too tightly. You'll need to adjust alignment of the holes before tightening the assembly. Using the 3/16-in dowel rod, slip the dowel through the holes on one side and out the other as shown below. Adjust the sections as needed. Repeat for the second set of holes.

  1. Using a rubber mallet or similar instrument (the heel of a shoe, perhaps), pound the elbows and pipe sections together snugly. When finished, check the alignment once more as in step 2. If the alignment is off slightly, you should be able to twist the sections enough to restore alignment.

If you want to paint the frame, now is the best time before you insert the emitters and detectors.


Adding the emitters, detectors, and detector shields


Tools needed: Hot glue gun and glue

  1. Slip the emitters (LED) and detectors (PT) into the holes in the tubes as shown below. Push them from the outside of the frame in. The smaller diameter hole on the inside of the frame will prevent the components from going all the way through. Note the orientation of the legs in the figure below. One leg is longer than the other for each component. Use hot glue around each component to hold the component in place. Try to keep the glue away from the dome of the component, but if you get some stray glue on the dome, peel it off after it dries.

  1. Your kit includes two 1-in long cylinders painted black. The purpose of these shields is to cut down on the amount of ambient light reaching the detectors. Place one of the sections over one of the detectors and hot glue it liberally around the base. Repeat for the other detector. See the figure below.


Wiring the emitters and detectors


Tools needed: 15-30 W soldering iron, solder, wet sponge, wire stripper, needle-nose pliers, heat sink, electrical tape

  1. Use the figure below as a guide to connecting the wires to the legs of the emitters and detectors. For a 10-in square frame (interior dimension), cut each of the black, green, yellow, and blue wires to a length of 14 inches. Strip each end half an inch. You can create a spiral using the method described in the instructions for the control box. Then slip each wire on the leg of the component as shown below. Take particular note of which wires are connected to the long and short legs. Three more connections will be added later from the photogate cable so leave room for those. These are indicated on the diagram.

Wires added to photogate frame

  1. Strip the gray insulation from one end of the 3-conductor cable by 7 inches. Then strip each of the three conductors by half an inch. Wrap these around the legs indicated in the diagram below.

3-conductor cable added to photogate frame


3. Solder the connections if you haven't done so already. You may wish to use a heat sink or else solder each leg quickly. When finished soldering, bend each leg over to the surface of the tubing and tape it down tightly with electrical tape. It's important to separate the the legs of each component to prevent them from touching each other. Look down inside the hole to make sure the legs aren't crossing each other and touching. Once you have the legs taped down, wrap tape at strategic points along the tubing to hold the wire securely and prevent it from being snagged and accidentally pulled off the frame.


Adding the plug to the 3-conductor cable


Click on the photos for larger versions


3-conductor cable stripped

Figure 1

Step 1


The final part of the assembly of the photogate is to add the 0.25-in stereo plug to the free end of the 3-conductor cable. Begin by slipping the black jacket of the plug over the cable as shown in Figure 1 to the left. Then strip the wires as follows:

  • Strip the gray insulation back by 3/8 inch.
  • Strip each of the green and red wires by 1/8 inch.
  • Clip 1/8 inch from the end of the black wire. Then strip the insulation by 1/4 inch.

Wires threaded on the plug

Figure 2

Step 2


Lay the stripped end of the cable along the sleeve of the plug as shown. Thread the green and red wires through the lugs shown in Figure 2. Spreading the lugs out can make it easier to thread the wires. Make sure the black wire lies along the sleeve. Don't crimp the tabs around the gray insulation until after soldering is complete. Otherwise, the heat build up can melt the insulation and create a short.

Soldering complete

Figure 3

Step 3


Solder the lugs with the red and green wires first. Since there's a lot of metal, it can take a while to heat the lug before the solder will flow. In order to accelerate the process, first tin the tip of the iron with solder. Then hold the tip to the lug on one side. Touch the solder to the other side of the lug. Once the solder starts melting, it will flow quickly and create a good connection.


Solder the black wire last. Heat the sleeve from underneath with the soldering iron. Then flow solder into the channel.




Soldering complete

Figure 4

Step 4


If you had spread the lugs with the green and red wires, push them back into their original positions. Then crimp the tabs around the gray insulation. Check visually to make sure that there are no stray wires that could create a short.

Soldering complete

Figure 5

Step 5


Screw the black jacket onto the plug to complete the assembly.


This completes the assembly of the photogate frame. If you've assembled the control box, then you're ready for testing. Go to the operating instructions. If not, go to the control box assembly page.




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