Hello colleagues. Using the TV in a dark room sometimes causes eye fatigue due to the brightness of the screen. This is no discovery - you can turn on the lamp and you're done. You can also turn on the LED strip on the back of the TV and turn it off when you are finished watching. However, it is always an additional activity.
The project below concerns the automation of the above process.
The basic assumptions are: 1. Automatic switching on of the backlight when dusk falls. 2. Gentle and smooth brightening of the LEDs so that the viewers do not notice the moment of switching on. 3. A gentle fading after switching on the light in the room. 4. Maintaining the light for about 30 seconds. after turning off the TV - time to put the remote control down and get to bed (this is my case). 5. Non-invasive assembly that does not require interference with the TV circuits (warranty maintenance requirement).
I do not boast of photos here, because what is there to photograph. The device was built quite a long time ago and I did not think about DIY then.
I was once gifted with a damaged 24V / 2A power supply, which I managed to fix quite simply. Shapely and transparent design, importantly, the manufacturer regretted the silicone gel, making it easier for me to make changes.
Finally, the power supply and the driver fit into the housing, where I placed the necessary connectors on one side of it: - mains power socket - LED connection socket - photoresistor socket - potentiometer From the opposite wall comes a cable terminated with a power plug, which powers the TV.
For lighting, I used the remains of LED strips that remained after some robots, just - they were different. The 24V part, the 12V part, cold and warm. Just right for such a purpose. In addition, an aluminum section in the form of an angle bar and a light strip is ready.
I attached the strip to the sheet metal TV casing using the existing screws that fix the sheet metal rear wall.
The photoresistor is placed under the screen so that it is not affected by its light.
This is actually so much about the description of the mechanical structure. As for the electrical system, its expansion was a consequence of the implementation of the above-mentioned assumptions. It is, after all, nothing more than an extension of the well-known twilight switch.
In the end, the LED strips turned out to be too bright, so after finishing the works, I added resistors to balance the brightness of the background and the TV screen. The LEDs visible in the diagram are small "fleas" mounted only to illustrate the logical states in the system. It allowed me to start the system faster and observe the operation on the table.
I was interested in the activation detection system. The calculations showed that a 70W load (actually a bit more) is needed for the transistor to work. Current televisions (especially those of smaller sizes) consume much less current - in this case, you need to increase the value of the 2R resistor. It is worth paying attention to the transistor that the author used for detection - it must be a transistor with a high maximum collector-emitter voltage - BF459 has 300V. However, the peak voltage is 325V.
Thank you for your insight. As for the 2? resistor, it is more than enough. It is true that there is a 55-inch TV set here, so the power is sufficient, but it is worth noting that even though the power supply is equipped with APFC, the current is not fully sinusoidal. The above value was more experimentally determined than it resulted from any calculations. In addition, the layout was created in the workshop and the TV was at home. This effectively blocked me from seeing the shape of the current. In the end, I made a compromise to reduce power losses on the one hand, but to ensure correct operation with the lowest backlight on the other.
Transistor ... It's hard to explain here. I knew about 300V from the beginning. I assumed, however, that since it is the guaranteed value, it will hold these few% for sure. besides, I had nothing else at hand. The entire system was created from the so-called drawer "przydasiów".
Now I can see that it was possible to use eg BC848 after installing a Zener diode, eg 18V between the emitter and the connection of the "flea" diode anode with the M24 resistor.
The resistor circuit is cleverly protected by two diodes. The voltage across the resistor will never exceed 1.4V. So increasing the resistance reduces the power dissipated on it. In principle, the system must correctly recognize the power supply during sleep and when the TV is turned on. It would be best if it was about 20W. I wonder if it is possible to simplify it more - put the diodes of the optoisolators in parallel to the resistor (in parallel, each through a small resistor). Obviously you need to increase the number of rectifier diodes (you need 3 or 4 in series) to get the correct voltage for the LED optoisolators, but it should work. The advantage is that the need for a high-voltage transistor and the power loss on it are eliminated.
I admit that I treated the detection system quite superficially, as the simplest part of the system. I stayed with the first solution that came to mind. You can actually do it in several ways, including bypassing the transistor. The optocoupler diode conducts from 1.1V, so even these 2 diodes (and a slightly larger resistor) could be enough.
It would be best, of course, to have a TV nearby to be able to run the system safely. I was doing it "remotely" so I had to assume a worst-case scenario.
For me, after turning on the TV, there is a voltage of 5V (Panasonic).
For me (Panasonic TX-55EX620E) it also appears and I even initially considered using this signal.
I successfully healed this idea when I woke up at night and noticed that despite the TV turned off, the external disk light was on (!) And it was 3 or 4 hours after turning off the TV. It turns off after a while.
Interestingly, a few moments after turning off the TV, the disk also turned off, but I do not know what mechanism it turns on after a few hours with the receiver turned off. I have neither recording nor timeshift configured.
Besides, it was easier to use the current signal. One cable less.
Added after 30 [minutes]:
If any of your colleagues uses a similar receiver, please make a test and connect anything (e.g. a LED lamp with low power consumption) to observe the behavior of the USB port after turning off the TV and share the observation results.
Respect for such an extensive analog circuit, although it is known - it could be done more easily on an AtTina. But I'm not talking about it - load detection - what for? There is voltage in the usb sockets after switching on, the LED lights up in the spdif socket, you can do this detection much easier without "false alarms". In my Samsung, I connect the LED strip directly to the USB. The resistor and capacitor deal with the topic of soft starting and extinguishing, I do not have to wait for getting to bed, but my house's night lighting works all night. All you need is a few LEDs with a power consumption of several dozen milliwatts every meter or a ready-made 12V led strip connected by a 1k resistor or more in various locations in the house.
load detection - what for? There is voltage in the usb sockets after switching on, the LED lights up in the spdif socket, you can do this detection much easier without "false alarms".
I wrote about the madness in USB in # 7. I plan to use the optical link socket (he, he, he - for 2 years) for an audio amplifier. Unfortunately, there is a constant lack of time.
The entire system was built in a matter of hours, not including the mechanical part. All elements are general cargo filling the boxes in the rack, including the remnants of LED strips (part for 24V, part for 12V). The power supply fell into my hands. So it was enough to pick up a soldering iron, turn on the oscilloscope, look out the window and feel sorry for those who are getting wet and cold somewhere, experiencing the autumn fluff.
The system was a bit big, because I assumed strict conditions.
Well, in my case, in Samsung, I attach an additional audio amplifier and backlight to USB. USB turns off after turning it off with the remote control. Perhaps not all USB ports in this Panasonic TV worked like this, or after detecting the disk, the method of port power control changed. Again, in the monitor with USB ports, I used 12V strips and a step-up converter, you can adjust the power and it is cheaper to implement than the 5V strips.
Lighting for the TV is a nice idea, but only if you have an even wall (if the TV is hung on a wall bracket). I gave up at home, after the first start-up, although the coats were made solidly, with such contrasting lighting, all defects and unevenness can be seen at night. It stung my eyes terribly, I gave it up. Just such a non-technical note ...
Would a fuse in the circuit not improve safety? With a short circuit in the TV or worse, an overload on the diode and resistor, a lot of power will be emitted.
It would definitely raise, but I consciously skipped this element knowing that it is already in the TV's power supply. Even if there was a short circuit in the TV power supply circuits before the fuse, nothing would happen - 3 diodes would be damaged. Initially, "short-circuit" and before they fail, a quick fuse near the meter will trip.
Backlighting behind the TV is a nice idea, but only when you have a mega-even wall (...) at night you can see all the defects and unevenness. It stung my eyes terribly, I gave it up.
For me, the problem of unevenness does not occur due to the distance from the wall. The light blurs nicely creating a delicate glow. It was too bright at first. I could convert the power supply from 24V to a lower one or make a potentiometer with DC component regulation added to the triangle generator, limiting the maximum PWM filling, but everything was already assembled and hung on the back panel, so I added some resistors.
The LED strips are glued to the aluminum angle. Its base restricts the light from reaching the base of the TV, making the wires less conspicuous.