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Thread: blindspot monitor buzzer addition

  1. #61
    Join Date
    Dec 2018
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    Adding interior blind-spot LEDs for Golf R 7.5.

    It is often difficult to see the light in the exterior mirrors so I added a couple of LEDs on the dash. Having tested the mod for over a month I am convinced of their value and very happy. They mean that I have extra awareness of vehicles in the blind spots without taking my eyes off the windscreen-view to look over to the side mirrors which requires refocussing then looking back. That time of inattention could be serious.
    Also, now I have my external mirrors adjusted the way I like i.e. looking back up the road, whereas previously I had them set to take in the blindspot


    I wouldn't rely on the system completely as if you are making a turn or lane change I believe you should look over your shoulder.


    I apologise for the laymans' nature of the information presented.


    Be very aware that I am not a practical person or electronics expert, so whatever circuit components you use, please calculate the resistor values are appropriate. Also, see if you can attach the input to the yellow wire for the left-hand side or the green wire for the right-hand side as the install time would be extremely short (e.g. 20 minutes instead of an hour). For some reason I found the LED would never go out using that as the input. Try it first.


    Here's how I did it.


    A very helpful poster “Don” suggested to me to incorporate the simple circuit below to avoid any possibility of messing the can-bus although he says, relying on the VW circuit diagram, there are no CAN messages that will go through the mod. The most important reason for it is it provides a degree of electrical isolation between the driver circuits inside the oe system and the load from the new LEDs. My layman explanation of the circuit is that the input is connected to a wire that sends the signal to the o.e. Lamps in the exterior mirrors. That signal goes to the base of the transistor which allows connection between the collector and emitter and hence power to the added LED. R1 is a variable resistor to allow you to “trim” the brightness.
    “Don” kindly calculated the values of the components to suit the LEDs I chose.





    R1 is 347 ohms , made up of a a fixed resistor of 300 ohms and a Spectrol 25 x Turn Trimpot of 100 ohms.
    R2 is 20 K ohms
    The transistor is a 2N3904
    I THINK the LED is White 5mm Cree LED 45000mcd Round Clear Jaycar CAT.NO:ZD0290. I think these are correct but as I destroyed LEDs along the way and cannot confirm the replacements, you should calculate your own values to suit.
    Here is Don's information, but substitute your own figures for the specs of the variable resistor and LEDs you choose
    " To calculate R1 - we need to calculate VR in the diagram like this:


    VR = 13.8 - (3.2 +0.2) Volts = 10.4 Volts
    R1 =Volts/Amps = VR/(LED nominal current, 30 mA) = 10.4/0.03 = 347 ohms
    To choose the power rating of R1: Watts= V x I =10.4 x 0.03 = 0.3 Watts
    R1=347 ohms


    To calculate R2 - I need to introduce the concept of DC Current Gain (called "hfe"). You can think of this as the transistor "amplification factor" when switched-ON. Or said another way, it's the amount of transistor Base current (let's call this "Ib") needed to make the required current flow through the Collector/Emitter junction ( let's call this "Ic" - which is 30mA in this case)


    By definition hfe= Ic/Ib. Or Ib = hfe/Ic


    If you look at the spec sheet, you will find that the minimum hfe when the Collector/Emitter current=50mA is 60. Let's use hfe=60 since 50mA is close to our circuit current of 30 mA.


    So, this means that Ib needs to be 30 mA/60 = 0.5mA


    Now, assuming that the nominal voltage of Input in my diagram= 12V, the voltage across R2 = 12-0.9 = 11.1 Volts. And since we need Ib to be 0.5 mA, R2 = V/I =11.1V/0.5mA = 22.2K. For the sake of reliability, let's choose 20 K ohms


    R2 = 20 K ohms"


    Connection points
    Looking at the manuals that show the current flow for the BSM you see a yellow wire for the left-hand side and a green wire for the right-hand side. They run along the sill from the sensor in the bumper to the connectors in the footwell.
    You might think that tapping into those would be convenient. I found that point turned my added led on when the ignition button was pressed and the car does its brief test of the bsm system (i.e. before starting the engine). But the added led stayed on, even after the mirror led went out. If it can be done that way it would certainly simplify the job. Try it first.


    There may be points in the footwell plugs but I found them too awkward to access for my bad back.


    Another option may be inside the door but as far as I could see that required drilling out the rivets holding the speaker.


    I finally connected the Input to the circuit into the wires behind the mirror glass that go to the bsm lamp. . MK7 GTI MIrror Cap How to Install (Carbon Fiber and European OEM Brushed Aluminum) - YouTube


    For the 13.8V power & Earth I obtained and connected to a cigarette-lighter type plug which goes into a multi socket in the cubby under the infotainment system.


    With the cap off the mirror, I unbolted the mirror from the bodywork, withdrew the bracket and with my wires I followed the mirror oe wire bundle which goes down down a tube and out through the 1cm hole in the body that you see when the bolt is removed. The wires were then into the area of the door hinges.


    I bolted the mirror back up carefully avoiding pinching the wires.


    Then I routed the wires neatly behind the hinges and the black plastic cover of the oe wiring between the door and body.


    I removed the trim up from the floor and put my wiring behind. I also removed the trim panel at the end of the dash. The circuit (insulated electrically with hot-glue) now lives in behind. It is wrapped in bubble wrap to prevent rattles. I also printed out a note with a short explanation of the wiring with the circuit diagram for the benefit of anyone who finds and wonders what it is. I made the paper fire-resistant by soaking in sodium bicarbonate dissolved in water then drying.. The note is now in a small plastic bag with the circuit.


    I have a dash mat and the wiring to the LEDs run underneath, with the LEDs on top of the “eyebrow” in front of the steering wheel.


    You may find the BSM system becomes de-selected. It can be turned on in the Infotainmment Menu / Vehicle / Driver Assistance Settings,


    Here's the explanatory note in the end of the dash









    This circuit is buried in here somewhere and is duplicated in the same cavity on the other side of the dash. It enables a blindspot LED in front of the driver.
    A figure 8 wire is connected inside the external mirror to the + wire of the oe BS lamp. It then goes through the mirror, out through a mirror bolt hole then to the circuit at Input. The other half of the figure 8 comes from the – wire of the oe lamp then to the Earth. The oe BS lamp operates as well.
    If the BS monitor device in the rear bumper tells the oe lamp to turn on, the signal in the mirror also goes to the “base” of the transistor which allows C and E to pass electrons and the cabin BS LED lights up.
    The +13.8V and comes from a 12V cigarette lighter plug in the cubby in front of the gear selector and goes to the long leg of the LED and the the short leg to R1. The – of the plug goes to the E of the transistor.
    R1 is a variable resistor is a Spectrol 25 turn 0-100 ohm trimpot (to “trim” the cabin LED to suitable brightness) with a fixed 300 ohm resistor which ensures the LED does not burn out. R2 equals 20K ohms. The cabin LED is a ZD0196 5mm clear white 33000MCD
    Last edited by notaGolfR; 23-12-2021 at 11:00 AM.
    cars (chronological) Morris850, Morris Mini DeLuxe, Cooper S, Mazda 1500SS, hard times so some old Holden, old Falcon Ute, better times so second hand Lotus Elan +2 (6 weeks, hopelessly unreliable) Chrysler Valiant Charger 770, second hand Datsun 260Z + 2 auto, Mitsubishi Cordia Turbo, Nissan 200SX turbo auto for 20 years(wonderful car burning ZERO oil after 200,000km & no problems when sold.. should have kept it), Toyota GTS 86 auto, now Golf R Mk 7.5 DSG built Aug2018, white.

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