Toyota Hilux Vigo ceiling light LED modification

I replaced my Hilux interior light incandescent bulb many years ago with a LED array PCB. These are available from eBay etc. at very cheap prices. The advantage is higher light output, as the original 8W bulb is dim. The light tone of these cheap led replacements is often bad, as the CRI (Color Rendering Index) of cheap leds is poor. The appearance of the 36 LED array in the middle of the dome light is also a bit stupid. After some years of use, the leds have started to fail, and it looks even more stupid. I started to play with idea of designing a LED PCB which would fit nicely inside the OEM light. The target would be to get high lumen output, good CRI, and high reliability.

Note that even though I designed this LED replacement board for Hilux, it might suit also other Toyota models, e.g. Fortuner and Tacoma. Also many Corolla models have identical looking interior light. So if you decide to build this for some other model, compare your light carefully to pictures on this page first. Also, let me know if you have successfully used this board on some other vehicle than Hilux.

The LED drive circuit

It is always good idea to drive LEDs at constant current. There are a lot of different ways to accomplish this. If you want good efficiency, you could connect many LEDs in series and drive the string with current regulating boost converter. This is otherwise very nice solution, but it lacks redundancy. If one LED fails for open circuit, all the LEDs in the string would remain dark.

I chose to use simple constant current source using NPN transistors. The circuit is shown below. The Vbe of Q15 and resistance of R1 sets the current, which is this case is 0.6 V / 22 Ω = 27 mA. Since forward voltage of white LED is typically around 3 V, you can't put more than 3 LEDs in series in a 12 V system. With this circuit, the LED current stays constant if the car battery voltage varies. It is quite typical to vary between 10 V ... 14 V. The excess voltage is 'burnt' by the transistor Q1, so it must be able to dissipate the heat. I wanted a large LED array, so I used a total of 14 instances the circuit below. This is quite an overkill solution. Nice thing is that a single component failure will cause only 3 LEDs to go blank. Also the heat load is shared between many components, so a normal thin FR4 board suits fine, no need for alucore board or other cooling solutions.

The delay circuit

The Hilux interior light doesn't have delay (at least mine doesn't). So I have added a delay circuit, which is shown below. The +12V, ground and DOOR signals are already available at the ceiling.

When door is opened, the DOOR signal is pulled to ground. This activates the current source formed by Q32 and Q33, which charges capacitor C1 with ca. 27 μA current. The two emitter followers Q30 and Q31 buffer the voltage of C1 and provide the LED_DRIVE signal to the 14 LED circuits described above. The emitter followers amplify current, and therefore reduce loading of C1. Otherwise the current drawn by the LED circuits would drain C1 immediately.

When door is closed, the Q33 shuts off, and capacitor C1 is discharged through R35. As the voltage of C1 drops, also the LED_DRIVE signal drops. The LEDs will remain at constant brightness for some seconds, and then go out slowly.

The ACC connection is optional. That signal is not available in the ceiling. You have to run a wire from some place which has +12V when ignition key is at ACC or ON position. The purpose of this signal is to cancel the delay when ignition is on. When ACC is +12V, and DOOR at GND, the current from Q33 goes through R33. The 27 μA current through 100 k resistor sets the voltage at C1 to ca. 2.7 V, which is enough for the LEDs to light at almost full brightness. When door is closed, the lights go out slowly, without additional delay. This mimics the operation of interior lights in new cars, but with analog electronics instead of the microcontroller driven PWM.

If your car already has a delay, or you otherwise want to disable the delay, you can just leave out C1.

The board

The board is designed to fit into the OEM dome light without any modifications. It is fixed in place with the 2 original vehicle screws. I spent quite a bit of time drawing the board outline, but now it's perfect fit. The top side of the board has all the leds, as can be seen from the Eagle3D / POVray render below. There are some areas which would still have room for LEDs, but it wouldn't be possible to place them symmetrically. Symmetrical placement looks much nicer, otherwise it would look like some of the LEDs were broken.

All the rest of the circuitry is on bottom side of the board. There is room for component only on center of the board. The edge areas are utilized as cooling area for the BCX55-16 medium power transistors. All resistors and capacitors are 0805 size.

Design files and documentation

hilux_ceiling_light.zip                       Eagle .sch and .brd

hilux_ceiling_light_circuit_diagram.pdf   Circuit diagram in PDF format

hilux_ceiling_light_assy_dwg.pdf          Assembly drawing. Includes also bill of materials with Digi-Key part numbers. Click here for shared Digi-Key cart with all the parts!

Install instructions

After you have soldered the components, the install is easy. You should get a 'festoon adapter', it makes connecting quick and easy. Maybe you could make one from the original bulb if you first burn the filament with high enough overvoltage and the solder wires to terminals.

1. Set the switch to OFF position.
2. Remove the lens. It is easiest to pry open from the switch hole. Or just pull from switch hole with finger, straight downwards.
3. Remove the old bulb (it is HOT if it has been on!).
4. Install the festoon adapter. The red wire should be at switch end, as shown in picture below
5. Remove the two screws with Phillips no. 2 screwdriver. The lamp might become loose from ceiling, don't worry
6. Connect the wires from festoon adapter to connector X1 on PCB. Red wire to +12V, black wire to DOOR.
7. Put the PCB in place, check that the wires don't get squashed
8. Make sure that screw holes align with the threads on the roof. Tighten the lamp and PCB with screws (see picture at top of this page)
9. Now you can test the operation. Note that the delay is activated also when you turn switch from ON to OFF, so it doesn't shut off immediately
10. If all is OK, put the lens back. Done!

Result and comparisons

After all your hard work, the reward is improved lighting. The photo below is taken with my 15 year old digital camera in the middle of the night, only light comes from the interior dome light. Sharp picture at ISO100 without flash.

Then a few pictures which try to show how it compares to original filament bulb and the cheap LED upgrade. The three shots below are taken with identical shutter speed and aperture settings.

The two shots below compare the light distribution between the 36 LED array and my design. The input voltage was adjusted low enough to be able to see the individual LEDs. The 36 LED array has some dead LEDs but you get the idea. The camera white balance is not properly adjusted in these photos. The Cree JE2835 4000K LEDs really look neutral white.

For more information, see the project web page at http://kair.us/projects/hilux_ceiling_light/