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Assembly and Operating Instructions for Kits


Assembly Instructions for the Interrupter Photogate Cable Kit


Assembly instructions for other kits



The Interrupter Cable


About the interrupter cable


For this cable, the IR emitter and detector are housed in the U-shaped piece shown in Photo 1. In addition to this piece, you'll need the following parts:

  • 3-ft length of 3-conductor cable
  • 3.5mm stereo plug
  • 1-in piece of single strand hook up wire
  • 1 inch of 3/32" heat shrink tubing

stripped 3-conductor cable

Stripping the wires

  • At one end of the 3-conductor cable, strip the outer casing back by 2".
  • Cut the black and green wires 1/4" shorter than the red wire.
  • Strip the three wires back 1/4".
  • Cut the heat-shrink tubing into two half-inch lengths. Slip one of the pieces onto the black wire and the other onto the green wire Slip them back out as far as you can.

Soldering to the interrupter


The symbols and on the top view of the interrupter shown in Photo 4 refer to the LED and phototransistor (PT) respectively. The numbers refer to the legs on the underside (not shown).


The interrupter has short legs, so you won't be able to wrap the photogate cable wires around the legs. Use the procedure described below instead. This works but takes some patience and careful soldering. The procedure is described as if you're working alone. If you have an extra pair of hands to help you, that can make it easier.

Preparing the jumper wire

  • Strip all the insulation from the 1-in section of hook up wire. (This wire will be used to connect legs 1 and 4.)
  • Make a small loop near one end as shown in Photo 4.
  • Thread the loop over pin 1 of the interrupter as shown in Photo 5.

Soldering the jumper wire

  • Carefully solder the jumper wire to leg 1. The wires will heat quickly, and you won't need much solder for a good connection. Avoid dripping excess solder onto the base of the leg. This can bridge over to the neighboring leg.
  • Loop the other end of the wire around leg 4 and solder the connection.
  • The completed jumper wire soldered to the interrupter is shown in Photo 6.

preparing to solder the black wire

Soldering the black and green wires

  • For the black and green wires, there's not enough room to loop the wire around the leg of the interrupter. Instead, you'll just lay the wire on the leg parallel to it and solder the connection. See Photo 7.
  • If you're working alone, it will help to tape down everything with the black wire lying on leg 2. Then touch the solder and iron to the wire just long enough to make the desired connection.
  • Solder the green wire to leg 3 in a similar manner. The completed soldering is shown in Photo 8.

connecting the red wire

Photo 9

Soldering the red wire

  • Loop the red wire around the middle of the jumper wire are shown in Photo 9.
  • Solder the connection. This one's easy.

connecting the red wire

Photo 10

Positioning the heat-shrink tubing

  • Push the heat-shrink tubing down to completely cover legs 2 and 3. This will keep adjacent legs from touching each other. See Photo 10.
  • Shrink the tubing with the heat from a ligher or match.

Preparing to connect the 3.5mm plug


  • The photogate cable will connect to the project box enclosure with a 3.5mm stereo male connector. Remove the jacket of the connector and push it onto the end of the 3-conductor cable opposite the interrupter as shown in Photo 11.
  • Strip the gray insulation back about 1/4" and the individual wires about 1/8" as shown in Photo 12.

3-conductor cable with ends stripped for connector


Soldered 3.5mm plug

Connections to the plug

  • The terminals of the connector are numbered in Photo 13. The black wire will connect to 1, the green wire to 2, and the red wire to 3. If you have trouble getting all the strands through a hole, you can clip off the strands that won't fit.
  • Here are some things to keep in mind about soldering. First, don't crimp the tabs of the shaft around the cable before soldering. If you do, the heat of the soldering can melt the insulation and create a short. Secondly, tin the tip of the soldering iron with solder to improve conductivity. Then hold the tip on the metal near the wire to be soldered. Touch the wire to the metal, not to the tip of the iron. If you don't get the metal as hot as the melted solder, then the solder will bead up rather than flowing, and your connection may not actually conduct.
  • Photos 14 and 15 show two views of the completed soldering.

Connector with tabs crimped

connecting the red wire

Completing the cable

  • Crimp the tabs around the cable as shown in Photo 16.
  • Screw the jacket on to complete the connector as shown in Photo 17.
  • The completed cable is shown in Photo 18.





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