NuukiaWorld Project

Integrated LED flashlight for Nokia 6110

Have you ever wondered who really wants to carry those large key rings with a blue or white LED flashlight? I have. The thing I am carrying around is my phone. Phone is much more natural place for a flashlight than keys!

WARNING! Although the author succeeded in the operation described below, no guarantee can be given for the instructions. Opening and soldering components in a mobile phone contain always risk to damage the device seriously. Electrostatic discharge can damage the phone without any visible handling mistake.

Adding an LED flashlight into a Nokia 6110 phone is surprisingly easy. Only a suitable high-intensity LED and current limiting resistor is required. Because phone's power button can be used as a simple press-and-hold flashlight button, only one small hole is required (for the LED). This hole is drilled through the IR lens of the phone. There is just enough free space behind the lens for the LED and a minimelf-size resistor. Also power connections are near on the topmost circuit board, so long wiring is not required.

The original idea of a home-made phone flashlight was given by jet engine guru and scuba diving master Jussi Kaasinen in summer 2002: Jussi showed me his flashlight that was integrated into a Nokia 3310 phone. He had added a small button on the side of the phone to control the LED. In a few hours, I showed him my idea of using the power button of the phone to control the LED. However, it took more than six months for me to get time and a suitable LED to test my idea.

Finally, in the end of January 2003, I implemented an integrated LED flashlight for my Nokia 6110.

Background

There are two ways of integrating the flashlight into the phone. Because of the great reverse-engineering work made so far, it is possible to modify the phone software and include the flashlight functionality there. However, it requires tools and programs for writing the applying patch to the firmware and re-flashing the phone. For more details on this method, see NuukiaWorld's project "Software-controlled flashlight for Nokia 5110/6110/6150".

The easier (and NuukiaWorld's original) way is to build the flashlight so that it can be used without any software modifications. The rest of this article is based on this method.

Circuit Description

Note: Trying to adapt these instructions for another phone model requires extensive knowledge of the phone: You must analyze the power button wiring to see if the same LED circuit can be used in your phone. You need also to find proper places to get power for the LED. The worst thing is, however: there may not be enough free space in newer phones for a 3-mm LED!

Because I have special custom-made front cover on my phone, I did not want to drill any unnecessary holes in my phone. A hole for the LED can be drilled in the IR lens (I remembered that there is a little free space behind the lens in Nokia 6110). If something fails while drilling, the IR lens could be replaced. -- But there is no handy place for any kind of power button.

The phone keypad is connected as a matrix and it is not so simple to connect to any key without disturbing normal operation. However, the phone power button is a separate push-button switch that is used to send a signal to the charge controller ASIC "CCONT" for powering up the phone. (The button is also connected to the main keyboard for other functions like profile selection and switching off.)

The power button on Nokia 6110 is also stiff and shelteredly located. That is fine because you do not need to worry about draining the battery when you put the phone into pocket or carrying case. But the hardest problem is still not solved -- how to connect the LED flashlight to the power button without disturbing its normal function?

Surprise - it is very simple! By analyzing the Nokia 6110 circuit (see drawing) you can see that the power button simply grounds the PWRON signal on the UE4 User Interface module. The PWRON signal (connected on CCONT) is normally at the battery voltage (~4 V). The button also grounds keyboard signal ROW4. Because the core of the phone is operating at 2.8 V, the ROW4 signal is separated with diodes from PWRON.

The ground end of the button is connected to UDGND (User Interface Digital Ground). This ground net is connected directly to the minus terminal of the main battery. Controlling an LED with the power button cannot be simpler: just power the LED from the main battery plus terminal and let the power button ground the other end of the LED!

You might think about four remaining questions:

What about the power on/off function? If you press the power button to illuminate the LED, the phone is switched off. -- Usually you keep the keypad locked. While the keypad is locked, pressing the power button does not power off the phone. Ok, if you are not used to lock the keypad at all, it is your problem.
When the button is not pressed, the current may flow from a fresh battery though the LED to the PWRON net and damage CCONT chip. -- No. The voltage (4 V) specified for PWRON signal is nominal. PWRON signal floats almost at the battery voltage. Therefore there is no current through the LED while the button is not pressed.
Because the LED circuit is connected directly to the battery, you can drain the battery too empty by using the flashlight after the phone has switched itself off. -- Probably not, when speaking about white or blue LEDs. LED cannot drain the battery below its minimum forward voltage (usually ~2.5 V). In addition to this, light output of the LED fades away much earlier.
Can the extra current through the LED damage the UE4 or the main board? -- A normal blue or white LED tolerates up to 30 mA forward current. The display and keyboard LEDs of the phone are rated to draw 60 to 100 mA. The buzzer is rated up to 300 mA. Both of them are connected directly to the battery voltage VBAT. As you can see, the extra current is negligible.

The anode can be wired to the positive terminal of the main battery on the opposite side of the phone. However, because the display backlight and buzzer are powered directly from the battery, you can find the battery voltage directly on the UE4 board, near the top of the phone!

Building Instructions

You do not need so much for building this useful always-with-you flashlight: a white or blue LED, diameter 3 mm; a SMD (surface mount, minimelf-type is the easiest) series resistor, depends on the LED (something around 30 ohm); and a few centimeters of thin wire for wiring. Required tools are a soldering iron with very thin tip, thin solder wire intended for SMD soldering, Torx T6 screwdriver for disassembling the phone, good table-top drill, adjustable power supply & multimeter for testing, and of course ESD precautions (grounded tools, antistatic working place), soldering skills, and good luck.

Finding a good high-intensity white or blue 3-mm LED is not easy. In addition to high millicandela value you must look at the directivity of the LED. A small output angle focuses the light in the intended direction. 3 mm LEDs tend to have wider output angles and lower luminous intensities than 5 mm ones. I used an NSPW300 made by Nichia. (It can be ordered from Farnell with code 993-852.) Its luminous intensity is typically 3200 mcd, directivity is 25° and maximum forward current is 30 mA. Typical forward voltage is 3.6 V at 20 mA, so the phone battery will be able to drive the LED.

A current limiting resistor is always required. When the battery is charged, the charger sends voltage pulses to the battery. The voltage on the battery terminals may rise up to 5 V in the charging pulses. The charging chip "CHAPS" limits the charging current so that the highest possible battery voltage is 5.2 V for NiMH battery and 4.8 V for Li-ion battery.

LEDs are individuals. Use an adjustable power supply to find smallest series resistor for your LED that allows rising the voltage to 4.8 V (or 5.2 V) without exceeding the absolute maximum current of your LED. Work down from larger resistor values and never rise the voltage so that the maximum current is exceeded. The smaller resistor you can use the brighter will your flashlight be. Note that without charger the battery voltage is about 4 V. Therefore current through the LED in normal use will be about 2/3 of the maximum current. Luckily the light intensity does not decrease in same proportion.

Opening the phone

1. Open the phone by removing the battery and unscrewing four screws on the back.

2. After unscrewing hold the phone face down and lift the bottom end of the phone from the face cover. The upper end of the cover is locked with two clips near the IR lens. To remove the cover you have to slightly lift and push the phone to the IR-port direction. Do not use too much force.

Note: Hold the front cover of the phone face down. The earphone will be freed when removing the cover and will be then safely carried by the face cover. Do not touch the display lens inside the cover, the display itself on the phone, or the keyboard circuit board. Fingerprints are rather hard to clean.

3. Put the cover plate in a safe place face down and continue with the phone. Now you can turn the phone face up. You will see the UE4 User Interface circuit board, the power button, and some free space behind the IR lens (to the left from the IR module). Do not touch the components or the copper contacts on the circuit board if not necessary.

Testing the circuit

4. Use tape to press down the bottom part of the circuit board. Put a paper between the board and the tape so that keyboard contacts will not get dirty. The connector between the circuit boards is in the bottom part of the phone and there is no contact if the UE4 board is not pressed down slightly.

5. Using multimeter find out which pins of the power button are connected to the negative battery terminal. In my phone, two pins closest to the buzzer are connected to the battery minus (i.e. they are connected to UDGND), so the other two pins must be connected to PWRON. (There are several different revisions of UE4 board, so find out correct pins in your phone.)

6. Find a component that is connected directly to the positive battery terminal. In my phone the cathode of diode V28 (see picture, red wire) is the easiest place were VBAT can be found.

Testing setup (do not forget the resistor!)

7. Solder wires to these pins and connect the series resistor and LED to them. Be careful, the ground planes and other nets are very close to the pins. Avoid excess solder and double-check that there are no short-circuits.

8. Install the battery and test the flashlight by pressing the power button. After testing, remove the battery.

Mounting the LED

9. Use a marker to mark the optimal place of the LED on the IR lens. Notice the actual diameter of your LED (usually it is not exactly 3,0 mm). Note also the components on the bottommost circuit board when marking the place for the LED. In my phone there is an SMD capacitor just in the place of the LED (see pictures) but the LED fits exactly above it.

10. Try to pull the IR lens out from the phone. However, in some phones (like in mine) it cannot be removed. If you succeed in removing the IR lens, continue with step 13.

11. Unscrew the two screws on the upper part of UE4 and remove the board.

12. Unscrew the screw in the center of the RF block to remove the main board from the phone chassis. Be careful when removing the main board -- the clock backup battery may have stuck on the board and drop later! After removing the sensitive boards and the backup battery you can drill a hole on IR lens without removing it from the chassis.

13. Drill a hole for the LED on the IR lens. Use a very sharp twist drill and let it cut while using water or oil to cool down the plastic. Do not drill too large hole -- the plastic may melt slightly and the hole may be larger than you expect! Use a needle file to enlarge the hole until the LED can be pushed into it.

14. Fold the LED wires carefully using pliers as close of the LED body as possible. Do not crack the LED body while folding. Think carefully what are the best directions for the wires -- they may crack if you need to refold them. Before folding make sure that you can distinguish the anode and the cathode (usually the shorter lead) later.

15. If you have removed the circuit boards from the phone, reinstall the bottom one now. Do not install the cell structure on the board yet. Remember the clock backup battery.

16. Push the LED into its hole. If the hole is small enough, you do not need to use glue -- LED just sticks into the hole. Then remount the IR lens or the remaining UE4 circuit board. Cut the LED wires so that they will fit into the phone.

Wiring

17. Solder the series resistor on the other pin of the LED. Then use thin wire and connect VBAT (from the component you found in step 6) to the anode side and PWRON (from the power button) to the cathode side. When routing the wires, look inside the face cover. The silicon button covers the power button almost entirely and the same silicon part is used to seal the speaker on the UE4 board. There are not so many good routes for wires -- I had to route the negative wire over the screw near the power button as there were no space elsewhere (see picture).

18. Check your solder joints with a magnifier before installing the battery and testing your flashlight.

Assembling the phone

19. Hold the phone cover face down and push the top of the phone into the clips of the cover. After ensuring correct installation of the top part of the cover, push the bottom end of the phone onto the cover and screw the four screws back that were removed in step 1. Remember to hold the phone and cover plate face down until the screws are tightened. Do not overtighten. Probably you have to iterate the wire routes a few times while installing the phone cover, as there is so little space around the silicon seal.

20. Show your brand new flashlight to your friends. If you found this page useful, send your feedback to NuukiaWorld.

12.3.2006 nuukiaworld@gmail.com
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