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Build Your Own FRS / CB Radio J-Box

Here's a project you can build if you're trying to add music and a CB/FRS unit. This project will allow you to: connect a FRS radio or CB w/ the same type FRS connector (such as Cobra 45wxst), have a push-to-talk button, and also give you a switched auxiliary input jack for a CD player or radar detector. Total project cost is $20-$30 for parts and about 4 hours of labor.

The parts you will need for the junction box are:
2"x3" project case box, push-on momentary switch, on/off toggle switch, 1/8" input jack, 5-pin female connector, and a FRS type connector cable. You will also need to buy a 5-pin cable to plug from your junction box to your helmet. (Here you can buy coiled or non-coiled. My cable is a 5 ft., non-coiled, and runs under my tank bag.)

Layout of Junction Box:
(see pics) The push to talk button is on the front-left, the toggle switch is in the front-middle and the auxiliary input jack on the front-right. The FRS cable exits the right-rear side and the 5-pin connector is mounted in the middle on the right side. The junction box is velcroed to the top of my clutch fluid reservoir. You can chose your own arrangement, but this is what works for me.

Wiring the Helmet:
I wired my Shoei-RF 800 helmet with 2 speakers and 1 mic. The speakers came from an old pair of walkman headphones and the mic came from an old external microphone that plugged into an old, portable tape player. If you can find this mic, possibly at radio shack, the cable already has the FRS connection, which is 1/8" jack (speaker) and 3/32" (mic) jack. Hint: most chin pieces of helmets are made of styrofoam. Remove this chin piece and cut a hole straight through for the mic. Using a soldering gun tip, trace a path on the backside of the styrofoam. The heat melts away a small trench where the wires will be placed. Once the speakers are wired together (same color, or '+' to '+'), you should have 2 wires coming from the speakers and 2 wires coming from the mic. These 4 wires should be connected to a 5-pin (female) plug. The wiring order here does not matter but you need to take notes so you can wire the junction box correctly. (For this example I will use pin 1-2 for speakers, pin 4-5 for mic). My 5-pin connection exits the left side of my helmet.

Wiring the FRS cable:
 (Hint: make sure you leave enough cable to reach your radio or CB. My cable is only 9" long because my CB is mounted directly behind the junction box. Also, tie a knot in the cable to keep it from being pulled out of the box.) Take your FRS cable and test with a continuity tester to determine which jack goes to which wire. You should have 4 wires; 2 for speakers and 2 for mic. After you have determined which wires go to the 1/8" jack (speaker) and 3/32" jack (mic), label them or make note of the color. Connect the 1/8" jack wires (speakers) to pins 1-2 of the 5-pin connector (on the J-Box). Connect the 3/32" jack wires (mic) to pins 4-5 of the 5-pin connector. Congratulations! You now have a connection where the mic constantly transmits. Now, you must cut 1 of the mic wires and wire the push-to-talk (PTT) button in-line.

Wiring an auxiliary input:
 Wire one connector of the 1/8" auxiliary input jack to pin 1 of the 5-pin connector. Wire the other connection of the 1/8" input jack to 1 of the wires of the toggle switch. The other wire of the toggle switch now connects to pin 2 of the 5-pin connector. This switch cuts the input from the auxiliary jack, not the FRS cable. This is helpful if you're running a CD player or radar detector and want to temporarily cut the sound off.

Final words of wisdom:
Use heat-shrink insulation when possible and seal all connections/screws with silicon. The auxiliary jack is the only input which could possibly allow water to enter the unit. Find a rubber plug to seal it when it's not in use.

Article By: Wes Cameron  wescameron@prodigy.net 

August 2001 

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