I am in the process of designing a circuit for a project and am looking for some advice.
The project is LED Strip backlight (ambilight?) for a TV.
I want the backlight to turn on as soon as the TV is turned on. I was thinking of inputting 5V from TV's USB port to opto-isolator which turns the Arduino's power on and off. Arduino is used solely to set the suitable color with PWM.
I've added a schematic that I drew up and was wondering if that setup would work. I am worrying that even if I cut the GND line from Arduino using the opto-isolator and mosfet then the Arduino will still ground itself through the mosfet driver. Could that become an issue?
Possible solutions:
Should I use high side switching and switch off the 12V input to Arduino using P-channel mosfet? If so, what kind of mosfet would you reccommend?
Should I use an opto-isolator to drive the mosfet drivers in order to completely separate Arduinos power circuit from the TV's and from the LED strip's?
Television sets today are ALWAYS on. They are just on standby until you use the remote control to make them active.
I see no reason for an Arduino to be involved when you can get the control you need directly from the TV. On my TV, the USB port is a slave port, accepting data only.
I've checked the TV's USB port with my multimeter. It does in fact turn on and off according to the TV itself. I am using Arduino just to get the suitable color for me through testing various values for the PWM output. Cutting out the Arduino and generating the customisable PWM signal, for example 555 timer, is out of my league, I feel.
I think you're way overthinking it.
Power the Nano from the USB socket of the TV, same as you do when you program it, with a USB lead.
And only power the LED strip from the 12volt supply.
If you use logic level mosfets (the IRFZ44n is not), then you won't need the mosfet drivers either.
Use this first diagram, minus the diode.
Leo..
That is exactly the solution that I had for about a year, then my TV's display malfunctioned and got a new one under warranty. Now I'm hesitant to install the same system thinking that Arduino could have been the cause of the problem. I want to take extra precaution to protect my TV - hence the opto-isolator.
It may have been completely irrelevant to the problem. I just think it would be a good idea to isolate the TV's circuit from Arduino's. Could you help me with that?
If you use a good quality "plug pack" to power the LEDs, you have adequate isolation. The 30-odd mA used by the Nano is no more than any of the various devices - such as disk drives - that would be expected to plug into the USB port on the TV.
kasparx:
It may have been completely irrelevant to the problem. I just think it would be a good idea to isolate the TV's circuit from Arduino's. Could you help me with that?
