Cool Light Source From an Old Laptop LCD !

Ever thought of reusing old broken laptop LCD screen? yeah, actually you can make a cool light source out of it which is energy efficient and it's cool because you're recycling electronics.

Supplies

Old laptop LCD

LM317 ( Your own LED driver build )

Resistors 470E, 1.2k, 6.8E ( Your own LED driver build )

Soldering Iron

24V adapter ( Your own LED driver build )

12 V adapter ( Normal build )

Step 1: Identifying Your Screen

If you look at the LCD's backside there will be a serial number of the display and a manufacturers code. You can either google that number or you can search that in lcdscreen.com for the display type and data about the voltages current etc through its datasheet.

I found my data sheet through I was able to understand the basic necessary things such as input voltage and pins where it needs to be connected etc.

Step 2: Finding the Contact Points

Now grab a magnifier glass and be the detective to find out nerves (wires) of your cool back light. There will be following names in the board.

1. LED_EN or BL_EN

2. V_LED or VBL

3. LED_PWM

4. GND

We need only these 4 pins for our work.

Here the first pin is LED_EN as the name itself says it enables LED if powered high. According to my datasheet, this pin is named as LED_EN and rated as 3.3V.

Caution: Please check the voltage level before powering.

V_LED or VBL is VDD where we need to connect main supply voltage i.e 12V which will be boosted to the required voltage by the boost circuit and finally will be driven by the LED driver.

LED_PWM or PWM pin is where you provide the brightness control to the display. This is how your laptop display brightness is varied on your input Pulse Width Modulated signal. The measure is in terms of the duty cycle for the square wave PWM and is calculated as Ton/(Ton+Toff) i.e if Toff is zero PWM is 1 i.e 100%.

We will use the light as 100% bright.

The ground will be connected to ground.

Step 3: Connecting Everything

Before connecting wires you can remove LCD glass on the top, by removing side screws. LCD blocks almost 40%of light. Once you remove the LCD you will be left with bright white layers and transparent Fresnel lense sheet for proper dispersion of light. Be careful while rmoving LCD as it involves glass ! Use safety glasses and gloves. Refer the video for full description.

Once you get the required things you just need to solder the test points mentioned in the last step, after that, since we need logic level 3.3 at both PWM pin and the EN pin we will have to make a voltage divider which can reduce the output voltage like this.

Now you can turn on the supply, if everything goes well you'll be welcomed with a nice bright white light.

Here voltage divider determines the output voltage.

Output voltage = VCCxR2/(R1+R2)

In our case, R2 is 470 Ohm and R1 is 1.2K Ohm.

Step 4: Making Your Own LED Driver

In my case, my LED driver didn't work for some reason. I just designed a constant current source to drive the LED lights. This is necessary as applying direct voltages to those LEDs might kill them right away due to high current draw.

As you can see in the circuit there is a resistor which gets connected to the output pin and adjust pin. According to the datasheet of LM317, the voltage difference between the adjust pin and Vout pin is 1.25V hence by dividing a constant resistor we can get constant current.

Required current = 1.25/R

I have 8 LED's in series and 6 groups of them i.e 48 LEDs.

Each group needs around 30mA at 24V because (3V per led x 8LEDs)

Total current will be 180mA.

By using 6.8 Ohm resistor we can get around 183mA which is sufficient for our requirement.

The output is connected to LED input by directly soldering the wires to all negative and positive terminals of LED array.