Reference: instructables<3

I. Breadboarding

II. Eagle

Based on the tutorial of instructables, after calculation, with 9V input and yellow LEDs, I use 3 for 4 series, so total 12 LEDs, and the resistor connected to transistor will be 2.2k Ohm, and the one connected to emitter will be 22 Ohm.

The most challenging part is routing on the board. How to have an efficient route map without overlapping? Here I did a dangerous move, having a route under the electret mic, between its positive and negative hole. Don’t know if it’s doable or not.

[ UPDATED ] It’s ok to route under the mic, but should be careful not touching the pad –> adjust the width of the route to be thinner!