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!
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.
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.
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.
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.
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.
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!
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?
- 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
You might think about four remaining questions:
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!
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
intensities than 5 mm ones. I used an NSPW300
made by Nichia.
(It can be ordered from Farnell with code 993-852.) Its luminous
is typically 3200 mcd, directivity is 25° and maximum forward current
30 mA. Typical forward voltage is 3.6 V at 20 mA, so the phone battery
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
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
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.
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.
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.
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.
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.
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
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.
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.
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
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
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.
17. Solder the series resistor on the other pin of the LED.
use thin wire and connect VBAT (from the component you found
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).
your solder joints with a magnifier before installing the battery and
testing your flashlight.
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
20. Show your brand new flashlight to your friends. If you found this page useful, send your feedback to NuukiaWorld.
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