The previous page described how the microcontroller calculates the LED voltage and resistor. Finally, we’re going to solder up a PCB and demonstrate the test tool.
Below is the printed circuit board file for this project.
Click on the file and save it.
Download Copper Connection, the PCB layout software.
Free to display, edit, and etch at home.
Choose 'Bill of Materials’ from the Data menu in Copper Connection to get the parts list. Then solder the parts as depicted below:
LED Tester Pro motherboard
I used sockets for the microcontroller and LCD display because the tool was going to be assembled and disassembled multiple times during development.
The trimpot dial is going to be adjusted often enough that it needs to be sturdy. The original LED tester had a fancy multiturn trimpot with three inline leads. It was constantly wiggling away when I was trying to turn the tiny screw with a screwdriver. Learning from that experience, the finger-friendly trimpot is soldered flush to the board edge, with pins soldered to both sides of the board.
Trimpot soldered to both sides on PCB
Let’s see the LED Tester with Display in action:
I guess it is time to retire the original LED tester and the spreadsheet. There is something I really like about having a standalone, compact tool that does exactly what I need.
Display showing LED voltage current and recommended resistor
The board has been revised slightly since this article was written. There are holes in the LED pads to allow test leads to be connected to an external LED. Also, a resistor and power connection have been added to connect to the LCD backlight.