Tech Article Title Author Date

An Illuminated Compass for the B5

michael - stanton 2005

For those who don’t have a navigation system and has to rely on road maps, a compass turns out to be a valuable helper. Whether you’re lost in a strange city or just want to know if maybe you’re on the right road but heading in the wrong direction, it helps if you know at least the direction in which you’re going.

I had gotten used to the little compass my parents had in their car, and after buying my A4, I wanted to get a compass for it, too.

These instructions are for the first B5 model, before the first facelift. As always, I assume no liability for any kind of damage.

I first got a no-name compass from a car accessories store, which soon turned out to be a waste of money. Looking for an alternative, I stumbled across this site on the net, which gibes instructions on retrofitting a rear view mirror with a built-in compass. The price of this mirror – more than € 200 – put a quick end to my dreams. (That’s roughly US$ 200; for the Canadians, that would be Can$ 200 + TX.)

So I went out to find a good compass. My requirements were:

  • Compensation: This allows you to correct deviations caused by magnetic fields in your car so that your compass will always give you the right direction.
  • Illumination: To use the compass even at night (a situation I found myself in during one of my very first trips) it should come with a permanent illumination which can be connected to the dashboard lights.
  • Compact dimensions for unobtrusive dashboard mounting.

  • After searching for a while, I finally found the Ritchie X10. It is a boat compass that comes with a mounting bracket, with which it can be mounted on almost any horizontal or vertical surface, and comes with 12 V LED illumination. It is available in black, gray or white.
    The illumination


    The compass comes with a green LED for illumination. The light intensity is low, and the green LED doesn’t look very good with the otherwise red dashboard lights of the A4, hence I needed a different solution.Parts needed:

  • 2 bright 3-mm LEDs, red (mine have 15 mcd)
  • 1 resistor, 240 O
  • Heat shrink tube
  • A pair of electrical wire (like the one that comes with the compass)
  • Tin solder
  • Silver foil or similar
  • Tools: Wire cutter, soldering iron, hot air gun (a hairdryer can be used as a substitute), scissors

  • First we’ll remove the lid of the compass. Press against the front right of the lower half of the housing, allowing the notch to come free, and gently pull up the lid here. Do the same on the left side, and you can push the lid backward and pull it up.

    In order to increase the efficiency of the illumination, we can install a little reflector. First, we’ll remove the LED. Then we fix the silver foil to the inside of the lid. I used write protection stickers for the good old 5.25" floppy disks – they are reflective.

    Now we’ll assemble our new illumination. The beam of the LEDs I uses has an angle of 25°; the LEDs have 15 mcd. (The original LED has about 4 mcd.)

    LEDs have a long lead (the anode) and a short one (the cathode). The anode must be connected to the positive terminal of the power supply, else the LED will not light. Most LEDs are designed for a voltage of no more than 3 V; if the output voltage of the power supply is higher, a resistor between the power supply and the LED is necessary to prevent the LED from burning out. For our compass illumination, we’ll connect two LEDs in series and operate them at a maximum voltage of 12 V, hence, a 240–470 O resistor will do.

    First solder the anode of the first LED to the cathode of the second. Then shorten these two leads to about 5–10 mm and cover them with a piece of heat shrink tube. Fix the tube by heating it with the hot air gun.

    Now we’ll solder the resistor to one of the two free leads: Cut the lead to 5–10 mm and do the same to one lead of the resistor. The solder the lead of the LED to that of the resistor.

    Next, solder the wire pair to the LED: Cut the free lead of the resistor to 5–10 mm; shorten the free lead of the other LED so that its end is flush with that of the resistor. Strip of 5–10 mm of the insulation of the wire pair, twist the ends and cover them with tin solder. Pull a piece of heat shrink tube over each end; the tube will later cover all bare metal.

    Finally, solder the wire ends to the terminals of the LED and the resistor. Pull the shrink wrap tube over the bare metal and fix it with the hot air gun.

    Now shorten the wire pair to the same length as the cable that came with the supplied LED. Strip off about 1.5 cm of the insulation, twist the ends and cover them with tin solder. If neither of the wires is marked (e.g. with a stripe along the side), I recommend marking the positive wire now (that’s the one connected to the anode of the LED pair).

    We can now insert the LED pair into the lid: First pull the wire pair through the hole at the back of the lid. Bend the terminals of the LEDs a little, like the original LED. You might also want to bend the LEDs apart so that their beams are not parallel but form an angle – ideally 25° (angle of each beam).

    The two LEDs together won’t fit into the plastic bracket that held the original LED, so pull them to the front a little further and place them there. The space is sufficient.

    Finally, replace the lid.
    Installing

    I decided to place the compass above the center console. It doesn’t get in may way there and is in a good viewing position for both driver and passenger. The cable goes right behind the faceplate.

    The supplied mounting foot happens to be too big for this position, so I had to make a new one.

    We need an aluminum sheet of about 20×50 mm. Cut it in shape, leaving a square of 20×20 mm with two nose-pieces on the sides, 10 mm tall and 15 mm wide.

    Bend the nose-pieces upwards. Drill a hole with a diameter of 3 mm in each; the clearance between the plate and the holes should be about 6–7 mm.
    Cut off the ends of the nose-pieces, leaving only 5 mm of material from the center of each hole. Then radius the ends using a file.

    With the supplied screws and rubber rings, mount the compass to the new foot. Put on a piece of double-faced tape – either the supplied one, or use a Tesa PowerStrip – and cut it to size.

    Just to be sure, hold the compass in its future position: In my car, its place is above the center console, between the center air outlet and the hazard light switch. If it looks OK, remove the protective film and push it in place.

    Now it’s time to to wire the illumination to the dashboard lights: It is easiest to tap one of the dashboard switches for that. Do not use the hazard light switch; its illumination is powered by the ignition. All other switches are illuminated only when the headlights are on.

    First we need to remove the radio. In case you don’t know how: first insert a nail file or similar object into the slot at the bottom right of the radio. Then push the end of the file to the right while reaching into the tape slot and pulling the right side of the radio a little forward. Then insert the file into the left slot, push the end of the file to the left and pull out the radio. Remove the cables at the back of the radio.

    Behind the radio you will find two screws, which you must unscrew with an 8 mm nut. Be careful, the washers fall off easily and will disappear forever behind the center console. (I’m speaking from my own experience!) The faceplate can now be pulled off to the front.

    Now reach behind one of the switches with your finger and push it out to the front. The second switch from the left is best suited for this, as it is directly underneath the hole through which we’ll pull our cable later. If there is no switch in this position, use the one just to its right.

    Next pull the cable through the hole above the switches on the left. Pull the switch out of its socket; the two contacts on the top left (looking onto the socket) are for the dash lights: The top left contact is the positive terminal; the negative is right underneath it and has a brown cable.

    Pull the cable through the small hole on the side of the socket. Use the nail file to push the wire ends into their respective contacts – remember to watch the polarity! Reinsert the switch into its socket and push it back into its place.

    To test everything, turn on the headlights. The compass illumination should come on now; if it doesn’t, something went wrong.

    Now put the faceplate back on. Watch the cable – it should disappear behind the faceplate just below the compass. Insert the two screws again and tighten them.

    Finally, reinstall the radio. Plug in the cables at the back – the plugs are coded and cannot be swapped or reversed – and reinsert the radio. After turning it on, it has to be unlocked before it can be used again – refer to the manual.
    Calibrating

    Our compass should now give us the direction the front of our car is pointing to. However, various magnetic fields in our car cause it to deviate so that the display is probably off by a few degrees. We have to calibrate the compass.

    What we need:

  • The supplied screwdriver (it’s made of copper and hence non-magnetic so it won’t disturb the compass while we’re calibrating it)
  • Another compass
  • Some open space (without any vehicles, power lines etc. in its immediate surroundings – an empty parking lot is fine).

    First make sure the slots of both screws are horizontal – there is no compensation in this position. Make all adjustments with the engine running in order to get accurate results:

    Align the car so that its front points north. Use the second compass to verify from a few meters away. Turn the side corrector until the compass reads North.

    Now align the car so that its front points east and verify with the second compass. Turn the front corrector until the compass reads East.

    Next, head south and verify with the second compass from a few meters away. The compass should read South now – if it doesn’t, compensate for one half of the error with the side corrector.

    Example:
    South = 180°
    Compass reads 160°
    To compensate: Turn corrector until compass reads 170°. ((160° + 180°) / 2 = 170°)

    Finally head west and verify with the second compass. The compass should read West now, else we have to compensate for one half of the error with the front corrector here.

    Just to be sure, we can head north, east, south and then west again, compensating for one half of any error observed each time. Unless there is extreme interference, there should be no more major deviations.



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