flashing LED - first project

I'm eager to start my first project, but I don't know how to do it.

Its basically an LED blinking twice, once at every 20 min.

I can tackle it in Arduino since its code, but I need something really small, the smallest possible! (the way that would be powered also needs to take this into account. a 9v battery would be too much. but If it could have a way to be powered by USB that would be great).

The closest I can find, is something similar: A fake car alarm, that flashes a red led. But I need to have the 20min spacing! 

Can I have some shared knowledge ? :)

Thank you!

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iceng4 years ago
OK here is a circuit that will blink the yellow LED every 20 minutes after adjustment
20M.png
jlourenço1 (author)  iceng4 years ago
Interesting option, thanks a lot for the trouble. By the way, this project had a strong background on it, it was to mark the intervals that a computer user had to make in order to avoid wearing glasses in the future. Not innovative, and always a blinking LED at the end, but at least a good path to be wasting time I believe :) thanks to all of you, great community.
DragonDon4 years ago
I wrote up an 'ible on a flashing LED. Should be easily to use for your use. Just change the capacitor(or maybe a resistor...still new to this stuff) to change the blink rate. Small enough components to fit into pretty much anything. You could simple alter the design specs by setting up a circuit that uses a 'watch battery' I'm sure.
Heh, might help if I left the link eh? https://www.instructables.com/id/My-First-Circuit-A-Blinking-LED/
jlourenço1 (author)  DragonDon4 years ago
thanks, in my case I was told a 555 timer wouldn't be enough because of the time length being so long, so for the same size the ATtiny85 for 2 pound was enough :)
verence4 years ago
"but I need something really small, the smallest possible"

If you really mean it, contact some Chinese LED manufacturers. For a few dozen grands, they will incorporate a small controller into an LED housing. Not cheap, but very small and you will get at least some thousand of your blinking things... Okay, I'll stop kidding.

As you want 20min, you would need really big capacitors for the slow frequency or, if you use a smaller capacitor you will get a higher frequency and need a counter/divider.

IMHO, a microcontroller is your best bet. BVut not a complete computer like the Arduino, but just the µC itself. Look for something like the Atmel ATtiny. Its just a 8 pin chip and can run with an internal oscillator. There are even some versions in a TO-23  SMD transistor housing. Only 6 pins, but more than enough for your blinker.
jlourenço1 (author)  verence4 years ago
Thanks! Setting the time through frequency was a new concept for me. I knew that at a small scale there was no coding, but still it surprised me, since its not my area. Those microcontrollers, to my noob eyes, look like the 555s i was looking today, so i need to explore it. How is the time span controlled in this case? Also, since its a single isolated piece, this seems to add the work of assembling the circuit board from scratch, am i right?
There is a whole line of Attiny's, Attiny45, 85,... You can program them using a PC with the chip interface thing through USB or backpacked onto an Arduino setup like I have. You can then wire up the bare Attiny with an LED, resistor and coin cell battery. The coding is pretty simple to just use a counter to control the time elapsed and then blink the LED. There are lots of instructables on how to program them. Good luck.
Yep. You wont need more than the ATtiny and maybe a resistor for the LED. The oscillator is internal (not very high precision, but as long as you don't mind to wait 20.1 minutes instead of 20.000.. you should be fine). All your program has to do is initialize the pin with your LED as output, count for how ever long 20 minutes is divided by the operating frequency, switch the LED on, count for how long it should be on, switch the LED off, rinse, repeat ...