Cisco 7940 Backlight





Introduction: Cisco 7940 Backlight

Add backlight to your cisco phone screen!

The following instructions are for the telephone model Cisco 7940 only. Please take into account that on newer models of the Cisco telephone, the rear side of the screen is fixed with a circuit board that can not be separated.

Items used:

EL Foil (luminescent film) 112x87mm (any color: red,green or blue)

Power module adapter for MB102 breadboard with USB and DC power input.


2 LEDs 3mm (with the same color as the luminescent film)

Jumper wires

WE5-50 Inverter

Tools for soldering and reassembling the phone

Step 1: A) Phone Disassembling and Luminescent Film Installation

1. Weld the two tiny connectors of the luminescent film to a wire, be very careful and take into account that the heat irradiated from the welder can damage the luminescent film.

2. Disassemble the phone and remove the LCD display from the frame. This is the most difficult step as the screen is glued with double-faced adhesive tape. Gently bend the frame very slowly away from the LCD being careful not to break it.

3. Once you are done, remove the reflective foil layer at the rear side of the screen. Be careful and DO NOT REMOVE the thicker foil layer for polarization, otherwise you will not see anything on the screen!

4. Insert the EL-Foil between the plastic frame and the display. Before doing this step, I suggest you to try to clean somehow the glue on the rear side of the screen before inserting it on the frame to avoid the luminescent film sticking to the screen, otherwise you'll see a very annoying blur on the screen.

Also make sure that you put the fluorescent side of the luminescent film against the screen!

5. Put the screen again inside the frame with the luminescent film between the frame and the screen.

Do not reassemble the phone before completing the circuit process step.

Step 2: B) the Breadboard Circuit.

1. Put the power module adapter on the breadboard, and connect the power input with the jumper wires to the power lines on the breadboard. (+ and - on the scheme)

Please check the scheme representation and pictures.

* In case you have never worked with a breadboard, you should know that the left and right side of most breadboards are connected from top to bottom, and the two columns are used for power supply, one column for positive and the other for negative.

2. Put the WE5-50 Inverter on the breadboard, remember the lines are connected in groups of 5 points from left to right, so the inverter should be installed in a way that every pin is in a different line.

3. Connect the inverter to the luminescent film. You should connect the two bottom pins to the power out columns where the luminescent film will be connected. Connect with wires these points to the luminescent film.

If everything is allright, now you can plug an USB (or AC 5V) to the power module adapter and the screen should turn on and you should be able to see your screen at night from now on.

I skipped the LED process, if you want a more homogeneous and beautiful result, you can change the phone leds with color leds that correspond with the luminescent film color.

These instructions are not final, I will be updating it with new pictures and revise the instructions in the future.

If you do not know what you are doing and you do not feel confident with the process,I suggest you to start with easier projects as you can break your telephone!

I'm not responsible for any problems that may happens when doing this process.

Do it at your own risk!

If you feel confident and go on and end up with satisfactory results, I will be very happy to know.




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Hey OP, add the pics and update this like you said you would? ;P

Ooo awesome hack! Makes is so much nicer looking, and you can actually see it in the dark! Thanks for sharing!