Sunday, January 27, 2019

considered physical layout

Needed to do some board layout work with the physical components of the new dew heater controller. Sort placement and spacing issues now that I had a working prototype.

Used ExpressPCB once again. Copied the Sayal 103 perforated board layout from a previous project. Adjusted for wanting a number of diodes and resistors in a vertical orientation. Happily I found the old TO-18 transistor package in the component manager. Tried to space things out away from the power transistors and their heat-sinks all while keeping the layout as compact as possible. It was clear I would need a lot of jumpers. This was feeling more complex than the barn door tracker build...

Something new this time: I printed the board layout I created to paper. I was pleasantly surprised to find it was scaled perfectly. I laid it atop the perf board and used a push-pin for the through-the-hole lead positions. It worked really well.

I stared at the schematic for a long while. I rigorously checked all the nets. Everything seemed OK. I was certain I had not wired it up wrong. The next stage was important!

[ed: I am not including the image of the PCB from the software is it had errors at this stage.]

On the generous project box, I considered where to place the knobs, switch, RCA plugs, LEDs. Oh, and the fuse. The found fuse holder was big... But it looked like there'd be room.

I examined photos of do-it-yourself projects and commercial units in the interest of mimicry. How did other people arrange things? I was drawn to symmetrical styles.

Then, for the first time ever, I dove into old 123D to look for physical collisions. Cool! This was rather profound in helping me ensure that the circuit board elements would fit while not interfering with the case components. The TIP31C transistors with their heat sinks literally needed some breathing room, the business-end of the 1 mega-ohm variable resistors were big, and the fuse holder was rather long. I made a rectangular prism to represent the PCB volume. Turning the case transparent in the three-dimensional software let me see what might happen.

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Later, when I removed the fuse holder from the project box, knowing that I could rely on the fuse in the CLA connector, I reworked the case.

planned box layout for the custom dew heater controller

Lots of room inside. And I could easily create a balanced look. And I think it's a smart layout with outputs on the left and right sides. If placed horizontally at the telescope, some heating elements will be at the front of the 'scope and some at the back.

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