There’s a first for everything: custom PCB’s

February 21, 2011

When was the last time you did something for the first time? For me that is: just now. I am quite excited to have ordered my first ever custom PCB.

Some time ago I read about the Texas Instruments TLC5940 LED driver IC. It features 16 channels of PWM control with a 12-bit resolution, which means you can control 16 LED’s per chip and dim each LED form off to fully lit in 4096 steps. Or, you could use those channels to control RGB LED’s in which case you could address 5 RGB LED’s per IC and have one channel to spare. In addition to this, it is quite easy to daisy-chain multiple TLC5940’s together.

Texas Instruments TLC5940

Texas Instruments TLC5940

I ordered a sample from TI to experiment with in combination with an Arduino Uno and with the help of the Arduino Playground I found out how to hook them up and a library to easily address each channel. And before I knew it I was able to get some example code running:

This was exciting! However, doing knight-rider style light-effects on a breadboard is only going to entertain for so long. I have a bunch of (200+) white 5mm LED’s laying around here, which cannot be easily fitted to the breadboard in large quantities, so I decided to finally take the plunge and try to come up with a custom PCB to make a modular PCB that contains one TLC5940 and 16 LED’s and connectors to string multiple units together. And with the help of two great tutorials by SparkFun (“Beginning embedded electronics 8: Eagle Schematics” and “Beginning embedded electronics 9: Eagle PCB Layout“), I designed this schematic and PCB:

Modular 16ch LED driver board schema

Modular 16ch LED driver board schema

Modular-16ch-LED-driver-board-PCB

Modular-16ch-LED-driver-board-PCB

I had them looked at by an electronics guy at work, who did not see any obvious issues with it, so I decided to order 10 of these from MakePCB.com today. From what I have heard their communication skills are below par, but the PCB’s are of good quality and the costs were lowest I could find with shipping to my address. Now the long wait begins!

Just to be clear: I do not have a background in electrical engineering, I am test engineer by trade. I did not know *anything* about pcb’s apart from what they look like in a device before I started this and regardless of if the PCB’s are completely correct or not: I was able to pick up all this knowledge online and practice with free and often open-source software, making this a very low barrier to entry.

As soon as I have those PCB’s I will solder the components to it, and maybe fix an error here or there, but hopefully show a great result! And of course, once the design has proven to be correct and functional, I will share them here with you!

To Be Continued…

5 responses to There’s a first for everything: custom PCB’s

  1. Any chance of sharing the PCB design ? (eagle file)
    I’ll follow the tutorials, but like to have a “backup plan”

    • Hi Martijn,

      Judging by your name, we could speak Dutch, but since the site is in english, I’ll stick to that so that more others can benefit from this :-)

      First of all, please excuse my slow response. I was on vacation and disconnected for a few weeks, which was nice for me, but meant your comment was still in the approval/pending process.

      About your question: Yes I plan to share the PCB design by making the Eagle files available that I created. However, as I received the first batch of the PCB’s from the factory in China, I noticed I made a mistake in the silkscreen labels (the outline for the LED’s is missing). In addition, I want to update the design by adding a decoupling capacitor.

      I have recently populated 8 boards so far and they do work fine without the capacitor and the missing silkscreenlabels are no problem either, but it does mean mistakes can be made easily. The decoupling capacitor does become important when you plan to chain several boards together. For now I have soldered one between the +5V and GND on the IC itself.

      So, I am going to update the Eagle design files and when done post them online. To be honest, I am not sure when this will be as I am in the process of moving my “hobby room” from one place to another. I will drop you a line though once I wrap things up and post them online so you will be triggered once the files are available.

      Regards,
      Arno

  2. Did you ever get around to correcting the PCB? Any chance you could add the Eagle files to this post?
    Thank you
    Gary

    • Hi Gary, I have not worked on the pcb since, because I got distracted with other things I wanted to build… like the pinball machine ;-) But I managed to dig up the files as I left them back then and uploaded those in a zipfile. It contains a .sch (schema) and a .brd (board) file. You can find them at http://wp.me/a2GtzJ-g4

      I hope you can use them, it anything these can serve as a starting point for your own project. Please keep me posted!