Building Climate Controller Circuit Board

With the main schematic established, the next (and arguably, most fun) step was to layout all the traces on the circuit board in preparation for etching the board.

Board Sizing

First, I need to know the outside dimensions of the board itself, which will be sized to fit into my Pactec CM6-300 enclosure that I got for the project. In retrospect, I kinda wished I had used this project as an opportunity to make a classy wood enclosure, but maybe that will be the next iteration.

Why the manufacturer did not think it'd be helpful to have common reference point for dimensions is beyond me:

there is no common reference point for dimensions

So, I had to use the old brain to calculate and layout the board size, as well as the through holes. I also measured the rear AV plug depths to add keep out layers, that way I won't accidentally place my tall relays too close to the plugs, as they are panel mounted on the rear of the enclosure. Here is the blank board ready for components:

blank board in eagle

Placing the Components

Then, we simply layout the components in a logical order. I try to keep similar components near each other, and also keep an eye on where there will be connections to the front and back of the enclosure. About halfway through, I realized my initial "keep out" areas were not going to work, as the Arduino with the USB pig tail took up a ton of space. There also needed to be plenty of clearance for the leads that would come from the plug ports and go to the board terminals. I rearranged things accordingly:

new keep out areas on board

Routing the Traces

Once the components were placed in reasonable locations, it became time to route each trace that would form all the connections for the circuit. There were a couple tricky areas which required adjusting components slightly. I was hoping to keep all the high voltage AC on the bottom of the board, but it seemed better to divide them on either side when they came close to the screw terminal connections.

Another concern, is if the wide AC traces between the power port and the relays can handle the current flow for the space heater, at 1500 Watts it will be pulling 12.5 Amps through these traces, and that seems like a lot for traces only 0.175" wide. I'll need to keep an eye on the temperature of those traces and maybe install some breaker or fuse for protection.

The last thing I need is this nice board bursting into flames after all the work that has gone into it. Just look at all of the pretty traces:

board ready for printing and etching

Now, it's on to printing out the photo resist sheets and trying my hand at etching a board; I've always used an iron with laser toner and acid, so this will be the first time with photo resist.

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