Illuminated CD box

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Illuminated CD box

Most cars in the BMW 8 Series were equipped with a radio-cassette player and a trunk-mounted 6-CD changer. While some of these systems were regarded to as high-end during the introduction days of the 8 Series, they have become rapidly obsolete in these times of hard disk and flash memory MP3 players. Despite this, a head unit with integrated CD player is a popular upgrade to give the E31's interior a more modern touch.

Even with a modern head unit there is still a cassette box behind the hand brake lever reminding to the car's true age. Luckily the cassette storage compartment can be replaced with a CD box.

Fischer CD box

For those who just want to get rid of the cassette box, BMW offers a multi-purpose storage compartment (51 16 8 108 911) that fits in the opening of the center console's rear covering where the cassette box resides.

BMW used to offer a CD box as alternative to the cassette box, but its production is discontinued. 8eights – member of the Roadfly.com BMW 8 Series forumdiscovered Fischer Automotive Systems manufactures a CD box that is a direct replacement for the cassette box. In fact, the original cassette box in the E31 turns out to be manufactured by Fischer too and both the cassette box and CD box share the same design elements. The Fischer CD box looks just as OEM as the original cassette box. It's a seamless upgrade to the interior.

Fischer Automotive Systems CD box

Requirements

Few things are required to install the CD box in the E31. Obviously the CD box itself and optionally a bracket to mount the box:

  • Fischer Automotive Systems C-BOX 6-CD universal CD box (21262): The CD box is still on sale in several automotive shops and is usually also for sale on eBay – often advertised as a CD box for Volkswagen and Audi.
  • Bracket (51 16 1 970 721): This bracket is only required for those who have the multi-purpose storage compartment installed – the cassette box is mounted with this bracket and it can be reused for the CD box.
Bracket, center console rear covering and top storage compartment


Illumination

Both the cassette box and CD box have a small window on each tray indicating whether or not there's a cassette or CD loaded. The indicator window is white for an empty tray, red for a loaded tray. At night the indicator is softly illuminated in the cassette box, but not in the CD box. The CD box does not have illumination.

The cassette box is illuminated by a single incandescent light bulb on the rear of the unit. The bulb's light is distributed and transported to the indicators on the front by transparent plastic light bars. A closer look at the CD box reveals the box is prepared for the very same kind of lighting system, but the actual parts are missing. It's unclear whether an illuminated Fischer CD box is just discontinued or was never even manufactured. Fact is there are no sources speaking of an original illuminated Fischer CD box.

Many people will already be happy with the Fischer CD box upgrade, but the perfectionists will want illumination in the CD box too. The lighting system from the cassette box is not compatible with the CD box. The light bar illumination system is simple and effective, but nearly impossible to manufacture with hobby tools. A new lighting system must be designed. Without the light bar, the lights must be placed directly behind the indicator windows. To keep the power consumption low and because there is very little room inside the trays, light-emitting diodes (LEDs) are the most logical choice as source of light.

Choosing the right LEDs

LEDs are available in many different packages, colors and intensities. It's important to pick the right LED for this application. Standard 3 mm or 5 mm round LEDs are way too big to fit inside a CD tray. Surface-mount technology (SMT) LEDs are the best option because of the availability of small sizes.

For this application the LEDs do not need to be very bright. The LEDs are placed directly behind the indicator windows and the lighting is supposed to be soft and nonintrusive. A brightness of a few millicandelas (mcd) already suffices. Because the LEDs are directly behind the indicators they should have a large viewing angle for an even indicator illumination. The viewing angle is preferably over 120°. To match BMW orange illumination, the LEDs' wavelength must be around 605 nm (600–610 nm). Anything outside that range will look out of tone in the 8 Series interior. An excellent choice for this modification is the Avago Technologies HSMD-C170 LED.

Avago Technologies HSMD-C170

  • Package: 2 mm SMT 0805
  • Wavelength: 605 nm BMW orange
  • Viewing angle: 170°
  • Luminous intensity: 8 mcd
  • Forward current: 20 mA
  • Forward voltage: 2.2 V
Avago Technologies HSMD-C170: Welcome to the world of miniature SMT components

The indicator window of each tray shows the status in white for an empty tray and red for loaded tray. But LEDs emit monochromatic light In daylight – without the instruments illumination on – the indicators will appear white and red depending on their content. But at night with the illumination on, all trays will be BMW orange with only a very subtle difference between empty and loaded. That's because monochromatic light doesn't work well with color filters and the CD box was originally designed for an incandescent light. Some people prefer the all-orange look, while others may want to retain the white and red colors. In case of the latter white LEDs are the only option as these are not monochromatic.

Connector between tray and enclosure

Placing the LEDs in the trays creates a new problem: The LEDs need electrical connection but the trays can open and close. Fixed wiring is not possible. There should be a connector between tray and enclosure that passes the electricity when the tray is closed and is disconnected when the tray is open. The mechanical resistance from the connectors should be low because the springs that push the trays out are not very powerful. Due to the construction of the CD box enclosure and trays, readily available connectors will not fit. The connector will be custom made but kept simple and easy to manufacture with hobby tools.

Connector between tray and enclosure

The picture above shows the build-up of the connector. The female part will be mounted in a trench on the bottom side of the tray and is made of two contacts, bent into something that resembles a hook, facing each other. The contacts are cut from a thin sheet of cold rolled copper. Both contacts are held in place by glue and a small plastic block between the contacts. The plastic block clamps both copper pieces in the tray's trench.

The copper sheet can be cut with a sharp knife. It's advised to make the cuts in multiple strokes with medium force rather than trying to cut through the sheet in one take. This will give the cleanest cuts and avoids bent edges. The copper is thin and can be bent without effort, but bending and straightening just a few times is enough to make it break. The bends should be right from the first attempt and not too sharp – leave the bends a bit rounded to keep the stress off the copper.

The male contact is made from a 2-pin header cut-off from a larger male dual-in-line (DIL) header with 0.1" pitch. It's best to start from a male DIL header with a tall base – usually 7 mm (0.275") high instead of the standard short headers with a 2.5 mm (0.1") base. There's a picture of tall headers in the next chapter. The headers will be clamped inside the narrow openings on the rear of the enclosure and the short headers may not have enough contact area for a good grip. It's difficult to get glue all the way inside the deep openings, so it is important the headers stay put by themselves. The headers should point straight forward, but because the openings in the enclosure are wider, the headers could rotate away from the correct position due to vibrations from driving and block the tray mechanism. If it looks like that may happen, the optional guides can be used to apply extra clamping force from the sides and to keep the headers in correct position. The rear side of the connector – with the wiring – will be glued inside the opening. That should secure the connector.

The openings are 1.9 mm (0.075") high, but a cut-off 2-pin header is slightly thicker. The header must be filed to the exact thickness. Always test fit in the enclosure as the dimensions of the openings may vary a bit. The same goes for the optional guides.

The male connector in the enclosure pushes the contacts from the female connector away from each other to provide good mechanical and electrical contact. It's important the female contacts never touch each other! If they do, there's a chance upon a short circuit when closing or opening the tray. Even though the male connector pushes the female contacts away from each other, there's possibly a short moment where both male contacts connect to the touching female contacts. This causes no problem for the LED – it will simply receive no current and not light up, nor does it cause problems for the car's electrical system because the current will still be limited by the resistors on the printed circuit board (PCB). However, although extremely unlikely, the resistors themselves may get damaged from the increased power consumption. Just make sure the contacts have an opening of about 1 mm and there will be little to worry about.

Modifying the trays

Start by soldering wires to the LEDs. This may prove to be a challenge with LEDs this small. The LEDs are way too small to keep in position with a finger while soldering and weigh so little they will stick onto the soldering iron's tip. Use some creativity to aid the soldering. For example, wrap a rubber band around the hand grips of long-nose pliers or needle-nose pliers so they stay shut and clamp an LED between the tips. Or paste the LEDs upside down on double-sided tape. Tweezers to handle the LEDs are no superfluous luxury.

Use stranded wire instead of solid wire. Solid wire may be too stiff and interfere with the tray's fold-down mechanism. Stranded wire is more flexible. Ribbon cable like used for older computer drives is excellent for this. It's thin, flexible and can easily be split in pairs of two wires. Cut the wires to a length of around 10 cm (4") and clearly mark one of the wires in each pair. The latter will help identifying the polarity of the LEDs later on.

Strip the insulation of the wires or wire pairs about 2 mm (0.8") at one end. Twist the bare wire strands and then tin them by applying solder with a soldering iron. Perhaps add a bit more solder than strictly necessary for tinning the wires. This allows the wires to be soldered to the LEDs without applying extra solder and saves a hand that can be used to keep the wires in place while soldering. Bend the tinned ends 90°. In the case of wire pairs, bend both wires up or down in the same direction and all pairs in the same direction with regard to the polarity mark.

Now tin the terminals of the LEDs. This will help the excessive tin on the wires flow onto the terminals and create a solder joint. Next solder the wires to the LEDs and pay attention to the polarity of wire pairs and LEDs. Don't heat the LEDs for too long – they can't handle heat very well. A few seconds is long enough. If it doesn't work from the first time, just wait a short moment between attempts.

Eject the trays and push the guides on both sides to remove the trays from the enclosure. Then remove the bottoms from the fold-down part of the trays. Just insert a small, thin flat screwdriver or knife between tray and bottom on the sides and the bottom should pop-off. Once the bottom is off, be gentle with the trays. The push-to-eject button, the indicator and its spring can fall out and get lost with the bottom removed. Note the trench that runs all the way from the rear of the tray to the indicator at the front. In fact there are two trenches on each tray – one on each side – but only one side has an indicator.

LED mounted behind a tray's indicator window with a drop of hot melt adhesive. The pictured LED is of a slightly different type than the one discussed in this article, but the idea is the same

Place the LED as shown in the picture above. It should be positioned central in the trench. Don't put the LED too close to the indicator – a short distance is necessary to get an even illuminated indicator. There's a plastic notch in the trench which indicates a good distance. If necessary make a small bend in the wires to avoid touching the indicator's spring. The indicator and spring must be able to operate freely. Use a carefully placed drop of hot melt adhesive to fixate the LED. Make sure the glue doesn't flow over the LED obstructing its light output. Hot melt glue has several advantages: It creates bonds more than strong enough for applications like this, yet it can be removed easily – if ever needed – when applied in blobs. Thin layers are more difficult to remove, though. Another advantage is the hardening time. Within a few minutes at most the glue is hardened enough to let loose and it reaches full strength in less than ten minutes. A disadvantage of hot melt adhesives is stringing, but the strings are very thin and cool down rapidly without sticking. The strings can easily be removed.

An issue is that the wires can be visible through the gap of the hinge when the tray is open and folded-down. A simple yet effective solution can be achieved by putting a small, think and flexible strip of matt black plastic over the hinge in the trench. Glue the strip only on one side – either on the tray or on the fold-down front. Otherwise it may obstruct the fold-down mechanism. Contact adhesive is a good choice for this.

Female connector mounted in the tray's trench. A few headers are shown as example

Place the female connector at the end of the trench and secure with contact adhesive. Pay attention to the glue area of the contacts as shown earlier in the build-up of the connector. The top of the contacts should be no further than 1 mm (0.04") away from where the trench widens. Cut the wires at length, strip, twist and tin the ends. Put one or two drops of hot melt glue along the trench to prevent the wire from bungling underneath the tray. Then solder the wires to the female contacts. This should be done with the tray on a flat surface and something heavy on it to keep the tray from folding. This maximizes the distance between LED and connector and makes sure the wires are not cut too short.

Apply some silicone grease or petroleum jelly like Vaseline on the female contacts to protect them against oxidation.

Modifying the enclosure

Apart from the illumination, there's another thing the original CD box lacks when compared to the cassette box: two rectangular cutouts on the left and right sides where the rear covering of the center console where the box will be mounted in, grips in. Actually the cassette box has six cutouts, but only two of them are used. These cutouts are not strictly necessary, but without them the tabs on the rear covering may push the box' sides somewhat inward. They also make the CD box sit correctly level with the front of the rear covering. Take the location and dimensions of the cutouts from the cassette box and mark them on the CD box. Don't confuse the top and bottom sides of the CD box now the trays are out. Use a 3 mm (⅛") metal drill bit to cut most of the material away and then finish to a rectangle with a small smooth file. The result should look like in the picture below. Test fit in the rear covering.

Additional cutouts in the CD box enclosure for the positioning tabs of the rear covering. If you worry about the position of the cutouts on your CD box because they are further away from the guides than shown in this picture, don't panic! There are two revisions of the CD box: a version with short guides and one with long guides. The pictured box has long guides

Inside the enclosure are two large spring blades that push the trays out. Remove these to gain some space to work inside the enclosure.

Cut new wires or wire pairs for the wiring of the male connectors. About 8 cm (3") will do. Strip, twist and tin the wires on one end, then solder them to the male connectors. Once again, put marks on the wires or use different colors of wire to indicate the polarity. Insert the connectors in the holes on the rear of the CD box and respect the polarity of the trays. Optionally insert the guides. It's important the male connector sits in the correct position because once glued it will be extremely difficult to get it out again. The connector should point straight forward and the connector's base should sit flush with the inside of the enclosure. A flat screwdriver can be used to push the connector level with the inside. The picture below shows a close-up of the male connector mounted in the enclosure.

Male connector mounted in the enclosure as seen from within the enclosure

Once in correct position apply a royal amount of hot melt adhesive on the rear side to secure the connectors. Try to get the glue as deep as possible to get the best hold on the connector. Due to the amount of glue it may take a while to cool down this time.

Circuit diagram and PCB layout

The circuit diagram of the illuminated CD box is very simple, but diode D7 may need a few extra words. LEDs don't take reverse voltages very well. If the positive and negative terminals are accidentally switched there's a good chance the LEDs will die. The diode protects the circuit against reverse voltages.

Circuit diagram and PCB layout. Caution: the solder side layout (left) is mirrored!

Parts list

  • R1..R6: Resistor 1 kΩ (see text)
  • D1..D6: LED Avago Technologies HSMD-C170 or equivalent
  • D7: Diode 1N4001 or equivalent

LEDs cannot simply be wired to the 12 V system voltage. A current-limiting resistor is required to protect the LEDs. Measurements showed a current of around 12 mA makes the indicator windows perfectly illuminated. Not too soft, not too bright. When using different LEDs, the given current may not apply. The resistance value of the current-limiting resistor is calculated as follows:

CDBOX00.png

Where

  • R1: Resistance [Ω]
  • V: Battery voltage [V]
  • VD1: LED forward voltage [V]
  • ID1: LED forward current [A]

Note the equation above uses 13.8 V instead of 12 V for the battery voltage. Cars are indeed equipped with 12 V batteries, but to charge such batteries a slightly higher voltage is required. That's why the alternator and voltage regulator deliver 13.8 V while the engine is running (in practice 13.5–14.5 V).

The value of 967 Ω does not exist in the popular E12 series. The E12 series offers only a limited set of twelve values and their tenfolds. The E12 base numbers are 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, and 8.2. The closest E12 value for 967 Ω is 1000 Ω.

The resistance was calculated against 13.8 V, but the voltage may peak at 14.5 V in a worst-case scenario (that's not entirely true in this case because diode D7 also induces a small 0.6 V voltage drop, but to simplify things just ignore it for now). To make sure the LED always operates within specifications, recalculate its current at the maximum voltage:

CDBOX01.png

The maximum current through the circuit is 12.3 mA – barely an increase over the current at the nominal voltage and well within specifications. If the current would exceed the specifications, a higher resistance must be chosen.

The resistor limits the current through the LED, but by doing so it also consumes power – power that's dissipated into heat. It's important the power dissipation is also within specifications. A standard resistor can handle only up to ¼ W.

CDBOX02.png

At 150 mW maximum power consumption, the resistor is well below the permitted 250 mW.

Everything is now ready to put the CD box together. If you wish to attach the PCB to the enclosure with screws, drill the holes before soldering the components. Use screws with a sunken head because there's little space behind the trays on the inside of the enclosure. Alternatively you can attach the PCB to the box with a few blobs of hot melt adhesive. Don't glue it until everything is soldered and tested! When soldering the leads to the connectors, pay attention to the polarity. The CD box circuit itself is protected against reverse polarity by the diode, but it doesn't protect the circuit against build errors.

The built-up PCB mounted to the rear of the CD box enclosure and wired up to the connectors. The PCB features a fuse holder with fuse, but that's completely optional and not necessary. An attentive viewer may notice one of the resistors is 820 Ω instead of 1000 Ω. For some reason the accompanying LED appeared less bright than the others, so the current through it was increased to match up with the other LEDs

Once built-up and wired-up, re-insert the trays and test the illuminated CD box in the car. The wire to the bulb of the old cassette box can be used to provide power to the CD box. The easiest way to splice power from this wire is by using quick snap wire splices, but another neat way is using the light bulb's socket with the base of a bulb. Just take a fitting light bulb and carefully break the glass – make sure the base doesn't crack. Remove the filament and support(s). Solder the wires to the exposed internal leads of the bulb – these are coated leads and don't solder very well. If necessary use a knife to remove the coating a bit. The wires now come very close to each other, thus provide sufficient insulation by using heat-shrink tubing. Use stiff heat-shrink tubing (or multiple layers) to encapsulate the bulb and leads, exposing only its base where it goes in the socket.

Turn the ignition key to I or II and turn on the lights. If no tray lights up, you have probably mixed up the polarity. Just swap the power to the PCB and it should work.

Illuminated CD box at night

In the dark, with all interior lights out, the indicator windows of the CD box should provide a soft and nice BMW orange illumination. If for some reason one or more trays are less bright than the rest, just replace their current-limiting resistor with the next lower value from the E12 series. Don't forget to recalculate the current through the LED and power consumption in the resistor to make sure everything operates within specifications!

Installation

The installation is very straightforward. Insert the CD box in the bracket with the bracket's mounting holes on top of the CD box and facing towards the rear side. The bracket should simply click in place. Then insert bracket and CD box in the center console's rear covering from the inside. If the extra cutouts in the enclosure were made, it should also click in place. Connect the illumination circuit board to the car's electrical system and put the rear covering back in the center console. Tighten the three screws and reinsert the top storage compartment. The picture below gives a good impression of the CD box installed in the BMW E31's center console.

Illuminated CD box installed in the 8 Series' center console and with a CD stored in the fourth tray

The author of this article understands that all attempts to make the car's interior look less dated fail when one leaves the prehistoric BMW cell phone in the car. The author has not yet decided what to do with it because it actually works surprisingly well as a hands-free telephone. But that shouldn't stop you from removing the mobile phone.