Introduction: Automated TV Bias Light
In this Instructable, we will make a TV bias light that turns automatically when dark.
This bias light is a simple device that can be added to any TV with the purpose of illuminating the wall behind the TV. This illumination reduces the perceived brightness of the display, reducing the eye strain and fatigue that occurs when viewing a bright display against a very dark background for an extended time.
Additionally, it also increases the perceived blackness and contrast of the display making that color pop so you can enjoy a better viewing experience, even on cheaper TVs.
Tools and materials needed to make this project (affiliate links):
- Soldering iron - https://s.click.aliexpress.com/e/_d8xmmf7
- Photoresistors (LDR) - http://s.click.aliexpress.com/e/_dZTauwN
- 2N2222 NPN Transistors - http://s.click.aliexpress.com/e/_d8HSvFx
- Asorted resistors - http://s.click.aliexpress.com/e/_dSIvhPF
- LED Strip - http://s.click.aliexpress.com/e/_Bf783rEt
- Protoboard - http://s.click.aliexpress.com/e/_dYLR0qN
- DC Jack - http://s.click.aliexpress.com/e/_dUiKB3j
- 12V Power adapter - http://s.click.aliexpress.com/e/_dYpFrWh
Step 1: Principle of Operation
The bias light is made out of a few components but the main star of the project is an LDR or light-dependent resistor. Often called a photoresistor, this device has a sensitive surface on the top and it changes resistance with the change of light on it. The more light it receives, the lower its resistance.
The circuit uses one LDR, 1 150K Ohms resistor, and 2 2n2222 general-purpose transistors. The LDR and the resistor form this light-dependent voltage divider that will turn on the first transistor as soon as the LDR has higher resistance as when the light in the surrounding is low.
This then turns on the second transistor that is solely used as a switch for the LED strip. You can use the circuit with only the single transistor, but in that case, the strip will not be powered with the full 12V from the input because of the voltage divider.
Step 2: Prepare the Circuit
Once I had the circuit ready, I replicated it on a piece of perf board, making sure to leave as much of the LDR legs on top as possible. These will later help us place the LDR in such a way that the light from the strip is not affecting it, but it gets its light levels from the ambient light in the room.
I’ve also added a DC jack to the circuit for powering it up with a 12V wall adapter and I left longer wires where the LED strip needs to be connected. These will be connected later when I mount the strip on the back of the TV.
Step 3: Test the Circuit
Before the final assembly, I made sure to test the circuit on my bench in order to make sure that it all works as expected.
Step 4: Install It on the TV
Once I had everything ready, I moved everything to my living room, and using the adhesive of the LED strip I placed it all around the perimeter of the TV. Make sure to apply the LED strip in such a way that it will not be visible from the front or the sides, as it only needs to illuminate the wall behind the TV.
I’ve also used my hot glue gun to add some reinforcement to the LED strip in a few places and also to mount the electronics board to the bottom left corner of the TV.
As a final step, I’ve trimmed and soldered the wires coming out of the board to the LED strip and I power it up to test and see how it works.
Step 5: Test Installation
Since it was day time and there was a lot of light the strip did not turn on but as soon as I covered the LDR with my hand, the striped was powered on as expected.
Step 6: Enjoy!
The true shine of the project came at night when we turned off the lights and the strip turned on for an awesome viewing experience.