Using SuperCapacitor for shutdown power of ATTiny85 powered by USB

Thread Starter

l8gravely

Joined Nov 7, 2008
2
Hi,
I'm building a simple device to help turn on my soundbar when the TV is powered up. Works great in my test board using an Adafruit Gemma. But I'm working to build a dedicated system based on an ATTtiny85 to send the IR code to the sound bar for power up and shut down.

But I want to power the device by the USB port on the TV. So when the TV is turned off, I'd like to have a super-capacitor (or even some other power storage device) with enough power to run for 10-30 seconds, while sending some IR codes to also turn off the soundbar.

So I figure a supercapacitor rated for 5.5V should be the right size voltage wise, just not sure what kind of uF sizing I need. And do I need to get some sort of converter to make sure it all works as the voltage drops? I'm trying to keep it all simple, but I suspect it really won't be.

The ATTiny85 has one IR LED output, and an opto-isolated input to check if the soundbar is powered up.

Hmm... maybe I just power the device from BOTH USB outputs, with seperate sense inputs for each, so I can tell what I need to do. Hey, they might actually work even better! If the TV is off, I just want to turn off the sound bar, which would drop the power to the unit, which is just fine. Nothing to get corrupted. And on power up of the TV, I see that the soundbar isn't working so I send IR code to toggle it's power.

So what would I need to do to avoid back-powering each source USB device? Any ideas or suggestions are much appreciated.
 

Alec_t

Joined Sep 17, 2013
11,401
Welcome to AAC!
Wouldn't it be simpler just to power a relay from the USB and use the relay to switch power to the sound bar?
 

Thread Starter

l8gravely

Joined Nov 7, 2008
2
Welcome to AAC!
Wouldn't it be simpler just to power a relay from the USB and use the relay to switch power to the sound bar?
Unfortunately no, since the soundbar doesn't power on when you plug it in. I have this working on a GemmaM0 from Adafruit running circuit python, but it's powered by an external wall wart which I want to remove. It's a hack! *grin* The goal is to A) clean it up nicely, B) learn something new, C) design my own board using KiCAD and D) make a nice enclosure too.

I did find an interesting Analog Devices LTC4417 which handles multiple power inputs and such. Unfortunately the packaging isn't ideal for self assembly, at least not at my skill level. LTC4417 datasheet and stuff can be found here. Again, maybe this is overkill too. I'll try to post my schematic when I get a chance.
 
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