Connect with us

Radar detector smart cord circuit

Discussion in 'Troubleshooting and Repair' started by Johnrobbinsjr, Sep 9, 2019.

Scroll to continue with content
  1. Johnrobbinsjr

    Johnrobbinsjr

    12
    0
    Sep 4, 2017
    Looking for some help understanding how this circuit for a radar detector smart cord works. Specifically how with two LEDs in series one blinks when the radar is alerting and the other one stays on constant. I would like to add a dimmer to the alerting LED, but I don't know how do go about this without effecting the power led. I appreciate any help you can provide. Although I do have a specific goal, I would like to understand as much of this circuit as possible including how the mute button works by grounding a certain lead to the radar.

    [​IMG]
     
  2. Martaine2005

    Martaine2005

    2,931
    799
    May 12, 2015
    I suppose it would depend on what the RJ11 signal is on B.
    And what the RJ11 signal is on Y.
    My guess is that there is more to this in the 'passport'.
    The alert LED is receiving a signal from B and the power LED blocks it. The transistor switches on/off during detection via Y causing alert LED to flash.

    Or Y is pulsed causing transistor to 'switch' and B is just negative..
    Dimming the alert LED can be done by adding a resistor.

    Martin
     
    Last edited: Sep 9, 2019
  3. Johnrobbinsjr

    Johnrobbinsjr

    12
    0
    Sep 4, 2017
    I'm sure you're right that there is more going on in the passport, I was just hopeful that we could take an educated guess of whats going on based on what I have. I don't know much about transistors, but I thought they had to have a positive voltage to switch. If that is true that would make Y a positive voltage, but how can Y positive when there is 680k resistor to negative on the same line? Also could the B from the RJ11 be a ground and the becomes dead when the radar alerts? When you say I can add a resister to dim the alert LED I assume I would do that between line B and LED?
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,370
    2,264
    Nov 17, 2011
    That is the most simple solution.
    Or between LED and the transistor's collector.

    One could also replace the mute button by a pwm circuit using e.g. a 555 timer ic (example). By modifying the duty cycle of the pwm generator the dimming can be made continuos.
     
  5. Johnrobbinsjr

    Johnrobbinsjr

    12
    0
    Sep 4, 2017
    Thank you for the advice. I didn't consider between the LED and collector. As for the PWM circuit, I understand that it used on/off signals to produce a frequency and power level, but I don't understand how replacing the mute button with this would enhance the circuit.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    10,370
    2,264
    Nov 17, 2011
    Read how pwm works (wikipedia). By adjusting the ratio of on time to off time the apparent brightness of the LED can be controlled. That is how LED dimmers operate.
     
  7. Johnrobbinsjr

    Johnrobbinsjr

    12
    0
    Sep 4, 2017
    Thank you Harald, that is how I understood it to work, but I'm confused to suggestion of replacing the Mute button with a PWM. Seemed like it should just inline in place of a resistor. Is that correct or am I still not getting it?
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    10,370
    2,264
    Nov 17, 2011
    As we don'tz know what happens to the right of the RJ-11 plug at pin Y, I suggest you disconnect the 10 k resistor to the base of the transistor on the side opposite to the base (where the mute switch is located). Then apply the pwm signal to the open end of the resistor.
    upload_2019-9-11_7-9-53.png
     
  9. Johnrobbinsjr

    Johnrobbinsjr

    12
    0
    Sep 4, 2017
    Thank you Harald and everyone else that offered their advice. I wish I understood circuits like y'all do. I really appreciate how people are willing to share their knowledge with anyone willing to ask.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-