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I needed a LED flasher circuitfor a simple giveaway convention badge/keychain for work. So I reached out to our resident expert @Wendy who helped me to narrow down some design ideas. We discussed using a 555:

CMOS 555 Long Duration Minimum Parts LED Flasher
CMOS 555 Long Duration Red LED Flasher
CMOS 555 Long Duration Blue LED Flasher
CMOS 555 Long Duration LED Flyback Flasher
This from Wendy's Index , The 555 Projects in references.

We discussed the criteria:
Must work on a 2032 button cell
Flash 2 LED's
Low cost
Easy to produce - which meant no microcontrollers which would add time to flash
minimal parts with small SMD components

This narrowed down to possibly using a CMOS 555 such as this from Wendy's library:
CMOS 555 Long Duration Minimum Parts LED Flasher

I looked at a simple transistor oscillator:




In the end I went with a Schmidt trigger oscillator. I used diodes to control duty cycle with separate charge/discharge paths. The final values were adjusted for the correct timing.





I designed a simple one-sided layout with SMD components


They came out very nice, was a great success! Thanks @Wendy


NOTE: I have removed all company logo and artwork.

 

Nice, did you have the boards manufactured?

 

Hi @BobTPH,
Yes, I panelized and had them populated at a fab house. They came in a day before the event. I had just enough time to pinch on a key chain and put batteries in, it was a small run of 280 pieces.

 

Nice project! Glad it worked out for you.

Easy to produce - which meant no microcontrollers which would add time to flash

For others reference, one can purchase microcontrollers pre-programmed, thus saving you the time and effort to flash large quantities of microcontrollers. I understand in your case this may not have been practical.

 

Unfortunately, this is the problem these days:
the TI schmidt trigger inverters cost about $0.05 each.

52week lead time:


this one could have done it, but it just adds costs:

 

I was asked for an order of this board as giveaways for a charity event. Since it's for breast cancer I will be donating them.