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Saturday, November 16, 2013

Started Making Circuit Board for HESA

Fridays are my regular time to work on projects at the Milwaukee Makerspace.  This Friday past I tried making progress on my Home Environmental Sensor Array.  Specifically, I worked on the circuit board.

There are many different ways to make a circuit board.  I am going to try three of the methods that I can do at the Makerspace:
  1. hand soldering components onto a breadboard, 
  2. using the CNC Engraver to grind away copper on a board leaving only the traces and drilling the holes, 
  3. using the laser cutter and acid to remove copper around the traces I want for the circuit.
PCB with Laser Cutter Process
First, some background on making a circuit board using the laser printer.  (I don't fully understand the complete process but here is what I know.)  Start with a copper plate that has copper on only one side. Cut out a piece of the copper plate that is big enough for the circuit board.  Cover the entire copper side with black spray paint.  (Any color will do but black is the most satisfying color.)  Put the piece on the laser cutter and print the pattern from DipTrace.  The laser cutter will burn off the black spray paint, revealing the copper. In the picture to the right, the black areas are where the laser cutter will remove the black paint. The revealed copper is where the holes will be drilled and also in between the circuit traces.  The next step is to use acid to remove the exposed copper.  The remaining copper is for the circuit.  After laser cutting, holes need to be drilled for mounting the components and to affix the PCB to the project box.  The final step would be to add the components to the PCB.

Designing with DipTrace

Before using either the CNC Engraver or the laser cutter, I needed to design the PCB in DipTrace.  I had it mostly done last time.  Tom G. helped me get the drawing ready to print on the laser cutter.

There are some things to know when designing a PCB in DipTrace (or probably any design tool).  The components should be put on the top layer of the drawing while the traces and holes should go on the bottom layer.  (The bottom layer is where the copper is.)  Also, Tom had me make the holes smaller and the circles around the pads bigger.  He also suggested that the trace width be a bit bigger.  All of this will make working with the PCB a bit easier.

One other designing hint is to put some mirrored text on the bottom layer.  This helps to know that you are looking at the right side when you do the print.  The standard is to put the letters RR on the bottom.  I already had my name there so we kept that and just reversed it.

Printout sample on paper
and painted copper
After getting the entire circuit done, we added a "copper pour" to tell the printer not to remove anything but the traces and holes.  In DipTrace, this is done by choosing Objects, Place Copper Pour.  Then, click on three of the corners and press Enter when the mouse is on the fourth corner.  A menu will appear with some options.  Make sure the "current state" field says "poured" and click OK. 

The final thing to mention is about printing.  When doing the print in DipTrace, make sure to click the Mirror and Negative boxes.  I think you would not check the Negative box when printing to the Engraver.

Using the Laser Cutter
I have not been trained to use the laser cutter so I will have to try printing the design some other time when there is someone who can help me.

Using the Engraver
I wanted to make a PCB using the CNC Engraver but it is in pieces right now so I could not use it.  I would like to use the Engraver because it will also drill the holes in the board.

Using a Breadboard
I was able to make part of the circuit on a breadboard.  I started by soldering a terminal strip in the middle of the board.  A ribbon cable will connect the raspberry pi to the terminal strip.  I used a multimeter to see if any of the pins were shorting each other out.  I did find two and had to remove some solder.  Next, I added resistors and sensor wires on each side of the strip.  I used the wires from the resistor to connect the components together.  The odd side circuit worked when I tested it with the multimeter.  

The soldering is not done yet.  It looks terrible and there are probably some shorts that I will have to fix.  Overall, it was fun so far and will be satisfying if it actually works without frying my raspberry pi.
Front side
Back side