The circuit would be very simple — just a 3 V, 1220-sized battery and two LEDs — and a pad for the lapel pin clasp on the back. The PCB must fit inside a 50 mm x 50 mm square to get the best ...

[jglim] didn’t have much experience with fabric, but a PCB lapel pin was something that seemed like it should work. There are really only three parts to a lapel pin — the small ornamental pin ...