Components for tiny LED chaser

Hi

I'm working on a tiny LED chaser with just 4 LED's. First I was planning to make it with a 12F629 and ULN2003, but I need to get it on a PCB that is less than 15x15mm (around 0.6x0.6 inch) so I think my prevoius idear is getting to big and a little overkill.

It doesn't have to be advanced, so now I'm thinking about using a NE555 to make the clock and another IC for the LED's.

My question is, what IC can/should I use for the LED's? I think a 4017 might still be big for only 4 LED's, what other options are there?

And are there any other options to replace the NE555 with something smaller? I would like to be able to change the speed if possible, but the most important thing is the size.

Hope someone can guide me in the right direction.

If the LEDs don't need much current, say < 20mA you can drive them directly from the 12F629. If you need more current, it would be simpler and smaller to use four transistors than a ULN2003. The PIC can deliver more current than a CMOS IC like the 4017 so you might as well take advantage of that. It also has an internal oscillator so you don't need any timing components like you would with a NE555 solution.

Brian.

Thanks, but it's still getting to big to use those components, so I'd still like more options if possible.

I have seen something similar on a small PCB, like this image, but I have no idear what is being used there and what's on the other side.

https://www.schmidt-teknik-hobby.dk/images/Rotary-PCB.jpg

I would guess that's all there is on the PCB. I can't see part numbers but the 'big' three pin device is probably a voltage regulator and the small 6-pin device is probably a microprocessor. To make a board no more than 15mm square you really need to use SMD components, it may be possible to squeeze through hole components into that size but it would be a tight fit! You could consider changing the 12F629 to a 10F200 which is even cheaper and the SMD version only has 6 pins. It can still drive LEDs quite happily and again has an internal oscillator.

Brian.

Thx, didn't know about that little 6pin pic. I'll have a look at those things

I have seen an inexpensive chaser that is the size of a button. It uses a "black blob on board".