With a medical device design already in the works, a local design studio enlisted our services to design them a small LED board with a switch and some logic. They wanted high output LEDs but wanted to avoid hot spots so we chose a small package size (0603) so we could fit as many as possible in the desired region of light output. These small LEDs put out about 900mcd each so there was plenty of light to fulfill their needs for the system.
All in the course of a 1 week timeline, we designed a small custom PCB, sourced the components and assembled and debugged. This design uses a current-controlled LED driver with on-board boost regulator for powering multiple LEDs in series. There is a current feedback loop to maintain very tight tolerances on the LED current and voltage. Finally, we added a flip-flop (1-bit memory device) to control which color is lit at any given time.
As it was for a medical device, all of the specifications were important for usability and quality. We worked with the customer's designers to determine the proper light output, switch force and components sizes/placement. They also wanted to be able to demonstrate to their customer and bring them into the discussion on light output. So we created a quick test jig so they would be able to easily power the board and control brightness of each color by way of 2 knobs on the box.
