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Assembly and Operating Instructions for Kits


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Crossed-Beam Photogate Frame 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


Tools needed: Saw (mitre box recommended), small round file, drill motor (drill press recommended), 13/64" and 1/4" bits or metric equivalents, rubber mallet, hot glue gun


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


Tools needed: Rubber mallet or equivalent

  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 about a foot length (the actual length depends on the size of your frame) of 3/16-in wood or steel 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, 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.

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 pipes 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 on the inside of the frame 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. If you have the CBP-F kit, two 1-in sections of 1/4" cylinders painted black are provided. The purpose of these shields is to cut down on the amount of ambient light reaching the detectors. If you don't have these, they're easy to make. Just paint a soda straw with black spray paint. After the paint dries, cut two 1-inch sections. 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


Note: We recommend waiting to solder until you've tested the operation of the assembled crossed-beam photogate.

  1. Use the figure below as a guide to connecting the wires to the legs of the emitters and detectors. Take particular note of which wires are connected to the long and short legs. Starting with the red wire, strip it back about half an inch, and wrap the wire tightly around the longer leg of the bottom LED. Work your way counterclockwise around the frame, connecting the wires. Some legs will have two wires connected to them.

  1. After you've wrapped the legs, go to this page and follow the instructions through Step 7 to build and test the breadboard circuit. Then return here.

  2. Assuming your crossed-beam photogate works correctly, go ahead and solder the connections to the components on the frame. See the tips below if you haven't done much soldering.

    Soldering Tips

    • Solder in a well-lit, well-ventilated, open area. Avoid contact with all metal surfaces on the iron.

    • Keep the tip of the soldering iron clean by wiping it against a wet sponge or towel before and after each use. A clean tip should look shiny and silvery; any yellow or black material on the tip will get into the solder and may weaken your solder joint.

    • Once the tip of your soldering iron is clean, touch a bit of solder to the tip just before use. This is called tinning, and helps the solder run more evenly.

    • Heat the connection to be soldered by holding the soldering iron to it, until solder applied at the junction between the two melts and flows freely. This ensures the connection and the solder are both hot enough to yield a good solder joint. This should take no more than 10-15 seconds. After the connection is heated, try to get solder along the entire length of the connection by briskly moving the solder and iron along.

    • Avoid touching only the solder to the connection, and then the soldering iron to the solder to melt it onto the connection. The connection will be cooler than the melted solder and won’t form a good solder joint.

    • Let new solder joints cool for several seconds before examining them. There should be solder all the way around the connection, forming a rigid joint. When done, unplug your soldering iron and let it cool.
  1. Use electrical tape to hold the legs of the components securely to the pipe. Make sure the two legs of each component are spread apart and not touching inside the PVC pipe. After securing the legs, wrap tape around the wires running around the outside of the frame to prevent something from accidentally snagging a wire and pulling it loose.

Connecting to camera or flash


Return to Step 8 on this page to connect a camera.




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