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  1. #1
    Join Date
    Mar 2009

    Default Home made smart cord


    Been reading the forum now for several weeks, but registered today so I could post.

    I picked up a 9500ix for use mainly on my motorcycle, and occasionally in the car.

    I'd like to wire up a semi permanent cable for use on the bike instead of using the included smart cord.

    I have several questions about this installation.

    First off, it appears the unit draws ~400mA during operation (max brightness). However, I'm sure when the speaker is going off during an alert situation, the current is much higher, probably upwards of 600-700mA ? So with this in mind, is the wiring in a regular 24/26 awg telephone cord sufficient?

    On a different site, i found the schematic for the smart cord. My intention is mount a remote bright alert LED that is more inline with my field of vision than where the RD will be mounted.

    Red = +12V
    Green = GND
    Yellow = mute buttom & alert led
    Black = alert led

    If i'm reading this schematic correctly, the black wire provides a ground (sink) for the power led under no alert conditions. When an alert occurs, either this ground is electronically disconnected or supply voltage is present - in either case, current flows to the alert led, while at the same time, a voltage is present on the yellow wire. Using the voltage divider circuit (10K & 680K resistors), the transistor is driven into saturation (turned on), permitting the alert led to ground.

    To make this function more so for alert purposes, the power led can be omitted as well. The 470Ω should not be omitted, but may need to be replaced with one of proper value based on current requirements of the alert led(s). The transistor used is a general purpose 2n3904 NPN type, with a recommended maximum current capacity of 100mA. Should be plenty to drive several 20-30 mA LED's, or one higher power led. Since it's used strictly as a switch, other transistors with higher current handling capacity are available.

    What do you guys think?


    Found this thread, DIY SmartCord... (Now Completed with Pics!!), specifically post #13 ( I disagree with the red and black being hot at all times. If that was the case, the power LED would never illuminate. There has to be a voltage difference for current to flow. Any flashing function is strictly controlled by the output of the yellow wire, which turns on/off the transistor (switch). If the RD is sending pulses, then it flashes.

    Edit2: Maybe I'm going about this the wrong way. Any one have any idea of on what the ear phone jack is capable of sourcing, specifically in terms of voltage and current? It would be much easier to just hook up an led or several led's via a 1/8" mono plug and call it a day. I need to use very bright LED's however that are visible in the day time.
    Last edited by jsolo; 03-13-2009 at 06:41 PM.

  2. #2
    Join Date
    Mar 2009

    Default Re: Home made smart cord

    Some others who are using various escort models suggest going through the ear phone jack. Any one have any definitive specs on how much current the jack is capable of providing?

  3. #3

    Default Re: Home made smart cord

    Bel/Escort doesn't provide any specs for the ear phone jack. I know that it can't source much current. The internal speakers on Bel/Escort models have an impedance of 38 Ohms. I do know that the maximum voltage at max volume at the earphone jack varies depending on the radar detector model, and of course the earphone jack is AC, not DC. Any DC current flow or ground loops for any accessory attached to the earphone jack must be blocked using a cap. Yet there is no reason I can think of why the earphone jack can't be used to properly drive the base a transistor which then controls a set of LEDs. Small LED light bar assemblies in various colors are available for dirt cheap on fleabay.

  4. #4
    Join Date
    Mar 2009

    Default Re: Home made smart cord

    MT, good idea. Some considerations however. If I use the ear phone ground to ground the transistor, the question remains if the RD can then sink all that current.

    OTOH, would using a chassis ground not cause any other issues/damage....

    Can you further clarify the need for the cap?


  5. #5

    Default Re: Home made smart cord

    I am working on recreating the entire Smartcord circuit in an electronics simulator program. That way I can then create and test various types of external LED circuits without risking damaging a Bel/Escort RD. I may get the simulator running later this evening -- otherwise sometime tomorrow.



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