Sense Check for Decorative Product Design Using Cheap MCUs from Hackaday Article

Hi all,



I’d like to ask you all for help doing a quick sense-check on a very basic design.
A lot less complicated than you're used to I'm sure, but I'd appreciate any little bits of advice before I get something made.
Background: 
Following reading a Hackaday about some extremely cheap mcus I decided to try making a basic decorative product, to develop design skills (electronic, manufacturing, and designing for commercialising).
I’m a Civil Engineer/Project Manager, been reading and experimenting for several years so skills and knowledge are on the medium level of self-taught.

I intended to post here but couldn't figure out a good way of inlining images for diagrams - so please see https://tinyurl.com/yy3t2l4t for a Google doc.
Cheers!

Dev,Unfortunately, the IT department where I work blocks tinyurl.com (along with other "personal" sites) so I can't comment on your design.
While you can't inline images in a posting, you CAN attach images and documents. You can add inline images to replies, however. Just be aware that they get shrunk when you do that.

Hi Elizabeth - the tinyurl led to a Google doc - can you access this: Proposed Design Google Doc?

Hi Dev-Apologies- I didn't notice that no one has responded to your request.Overall  I think you did a very nice job.  The only things I see to comment on are trivial.Although it won't hurt anything, I don't think you need the resistors from the low side of the switches to ground.
Don't forget to put a pullup resistor on the anode side of the diodes.
You'll gain a little bit of efficiency (better battery life) by using MOSFETS instead of bipolar transistors.  If you do, you won't need the base (gate) resistor.
While the way you're applying PWM will work, it's more common to apply it to the other side of the LEDs using a P-channel MOSFET.
If you do decide to use MOSFETS, make sure to select ones with a very low gate threshold voltage.
Your PCB layout is pretty impressive- especially considering that you haven't had any formal training in electronics.  Well done!Again_ I apologize that this went so long with no proper response.  This one slipped thru the cracks somehow.-Rick

Dev
I have a slightly different take to Rick-Yes, you should have the pull up resistor on the anode side of the diodes. The resistors to ground on the low side of the switches, may actually cause a problem- I am not sure of the characteristics of the micro and I am assuming a supply voltage of 3.6V. When the switch is closed the voltage on the cathode side of the is (3.6*470)/(10000+470)=0.162V. But add the volt drop (assume 0.6V) of the diode and the interrupt voltage is 0.162+0.6=0.762V. Is this low enough to be seen as a logic low? (especially across a wide temperature range). I would get rid of the resistors and use Schottky diodes (drop of ~0.3V) for good measure.Some micros allow you to PWM each output (or you can use the PWM to generate an interrupt and drive the inputs through software)  all in unison . You could then get rid of the LEDsink circuitry altogether and even (with individual PWM) adjust each individual brightness.Finally you are using a 100R resistor in the base of the transistors. At a supply of 3.6V the current required from the mico output is (3.6-0,6)/100=30mA. Again, I don't know the micro, but that seems quite high. I wouldn't exceed 10mA, and 5mA is more than adequate especially with the gain of a BC546.. I would use a 560R. Of course you can take Rick's advice and drive the LEDS with MOSFETs.Good Luck!