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Thread: Smooth out a Square Wave?

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    Default Smooth out a Square Wave?

    Hi,

    I have an aftermarket head unit in my car, when I hooked up the reverse camera power wire to the reversing lights the picture is unwatchable. From what I can research the lights are controlled by one of the modules in a duty cycle? (sorry for using incorrect terminology)

    When the ignition is on but engine off the picture is fine as it is getting constant 12+ but with the engine on the picture is as i said unwatchable.

    The internet suggested to run the camera power through a relay, getting the power direct from the battery and using the lights to the trigger the relay as the coil in the relay is too slow to re-act and effectively stays on. This solution 'almost' works.

    Is there a simple/easy way to improve my jerry-rigged solution?

    B



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    So, even when powered directly from the battery, there's interference?

    Have you tried ferrite suppressors with multiple turns of wire through them at both ends.... on both the power cable and the video cable?

    Poor quality video cables are also very susceptible to interference.
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    just out of interest , is the reverse camera hard wired ( connected via a direct cable to the head unit ) or is it wireless ? I had same issue in my mates car recently. His was a wireless connection which was a terrible picture but was perfect when we ran a AV cable to the camera.

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    Unfortunately new cars use totally unnecessary and complex technology to do a simple job. ie Turn a light on.
    They unnecessarily use Pulse width Modulation.
    First option is to put a diode in series and then a 100uF Capacitor to ground. May need to increase to 470.

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    Hi Again,

    MTV No sorry with the motor not running but ignition on, the picture is perfect. From what i read it is not interference it is the light signal being pulsed to illuminate, which efectivly is turning the camera power on and off as in a square wave.

    VroomVroom, yes the camera is hard wired all the way through.

    Reschs, That is the problem as I understand it, it is adding a level of unneeded complexity but it does tell you when a bulb is not working. Are you suggesting try a diode first the a cap if unsuccessful? If so is there a downside to just going to a capacitor? My basic knowledge is the the Capacitor stores the power and then releases it which sounds what I need.

    Brian

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    The diode is there so the that the capacitor only smooths the power to the camera and does not interfere with the normal operation of the car lighting system.

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    is the diode and cap in place of the relay 'hack' or in conjunction with?

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    In replace of. Same outcome.

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    thank you so much, I will try, and report back in a day or two

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    Quote Originally Posted by bop View Post
    Hi Again,

    .... If so is there a downside to just going to a capacitor? My basic knowledge is the the Capacitor stores the power and then releases it which sounds what I need.

    Brian
    Maybe a bit of background info will help here to explain why the diode is very important.

    This seems to be an LED lamp assembly and the LED driver is external. Lets say each individual LED must not have more than 3.2V so 4 in series is exactly 12.8V.
    That is a fully charged battery.
    The driver circuit detects that is still fine to run close to or at 100% pulse width. Basically it seems the LEDs are directly connected to the battery.

    When you run the engine the battery gets charged and quickly rises to around 14V.
    That is too high for the LEDS so the driver circuit start chopping, maybe at 80% pulse width, so for 20% of the cycle the power is down.
    This protects the LEDs but your camera sensor goes 'nuts'.

    When you try to smooth the signal just with a capacitor you are extending that 80% pulse width and giving the LEDs too much power. They will eventually fail.

    So putting the diode first in series(anode connected to the power+, cathode towards the capacitor+ and the camera sensor, then the capacitor- to ground) avoids the LEDS from 'seeing' the capacitor. The capacitor holds the voltage up on the cathode but as the diode is reverse poled towards the LEDs it can't discharge over them so they stay safe and your signal is clean
    So be 100% sure the capacitor is not parallel to the power but there is a diode in between.
    Last edited by Uncle Fester; 24-12-21 at 04:31 PM.
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    .
    Last edited by Uncle Fester; 25-12-21 at 10:40 AM.
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    Module to do this stuff -->>

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    OK,
    I have a 470uf 16v cap and a diode............. but i will by a module as wotnot pointed me to, I had seen those but had discounted them, as the mostly come from china and did not want to wait. BUT the relay that i installed is not horrible and i have decided to now wait on transport delays. Especially after Uncle Festers post adding even more complexity to the circuit.
    So thank you for all your help, I may have a crack if time allows, If i do I will report back but more than likely I will wait on a slow boat.
    Brian

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    Just realised, you were talking about the camera power , not a sensor wire so I deleted my last post.
    You would need the 470uF and an inductor to clean the power supply but that could also present another issue.
    The LEDs might be driven with a low side open collector circuit. That means 12V is always on and the negative is switched.
    I have that in some indoor lights in my car that uses PWM power to dim them but I am not sure about the tail lights..

    I assume that module from Wotnot's link would cover that.
    I think it is wise to wait for the module.
    Last edited by Uncle Fester; 25-12-21 at 11:08 AM.
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    AU stock listing -->

    The LEDs might be driven with a low side open collector circuit. That means 12V is always on and the negative is switched.
    Very often the case nowadays =)

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