Assembly Of Climate Controller Circuit Board

A lot has happened since the last update on the climate controller, namely I attempted to do the first photo etch, and over-developed the board, which messed up the traces. I did some re-design, and decided to try to do the old fashioned iron & toner method, but after making a reasonable board, found that I had reversed the pins on one of the components. Given that the board was already pretty ugly, I thought it would be worth just waiting for the new photo etch boards to come in the mail and do it right.

A Whole New Board Layout

While reworking some things on the board, I went through a few iterations, learned some things, and ultimately changed the way the board was positioned in the project box, as well as how the traces were designed.

  • By careful routing, all the traces are now on the bottom of the board; this saves with line up, and takes less time to prepare.
  • I made my AC traces as large as they could fit after finding some current calculations for trace size. This calculator is very helpful.
  • I also added a few extra pins to the analog, and digital busses of the Arduino, so that I could expand it in the future (such as adding the humidifier refill feedback loop).

Here is the updated board designed to fit around the mounting holes in the enclosure:

final board design

Etching and Assembly

With only a single-sided board, a new, thick piece of glass (to hold down the transfer), and a triple set of transparencies, I made a very clean exposure of the photo resist board.

Developing went better this time; after a minute or so, all the traces were visible and a quick douse in water stopped the process. Next, I put the board into the etching solution:

starting to etch the board

I used a mixture of 2 parts (drug store, 3% concentration) hydrogen peroxide, to 1 part muriatic (or hydrochloric) acid. Remember to wear gloves and safety glasses during this part, as you don't want acid in your eyes:

etch in progress

I like how you can easily see the etch, versus the dark ferric chloride. Once the etch was complete, the board looked really nice, with very good definition of the traces:

final board looks great

The board was then trimmed to fit the enclosure, and all holes drilled:

board fits the enclosure

Then, comes the satisfying task of neatly placing each component on the board and soldering it in place. This went rather smoothly:

components soldered on the board

I also soldered the ribbon cables to the smaller control board and the LCD, which now has all of its supporting components on the main board. Everything looks great and fits in the enclosure:

test fitting

Moving On

Now that most of the main electronics assembly is done, my next step will be to create designs for the front and rear panel, where the plugs and switches will mount. For these, I plan to do a custom layout and 3D print the panels for a really clean fit and finish. Stay tuned!

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