Weather station PCB’s and Stencil

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PCB

After YEARS of waiting, at least! (or it feels like that) The PCB’s for my Electric Imp based weather station finally arrived.

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Top side looks good, and even the ID number for the pcb’s, added by iTead, is placed under a relay, so it will be hidden when assembled. But for some reason the test for the different components are missing, could look like I screwed up with a layer or something.

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Bottom also looks fine, except the silkscreen looks a bit thin and the text got some holes in. A higher ratio for that should solve that problem.

All in all, I would call this is a successful prototype, so far. If it really is a success will be determined when all components are on and it has been tested.

Stencil

Designing PCB’s isn’t something I haven’t done before, but getting a stencil made is. Therefor the waiting time for this was something that could almost be described as excruciating. But the day has come! Same day as the PCB’s arrived! Let me introduce you to, my first stencil. 🙂

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So what is this thing actually? In all basics, it is just some kind of sheet with holes in. The sheet can either be made of plastic or metal, depending on how many times you plan on using it. The one I got made is from polyimide, it won’t last as long as a metal one will, but it is plenty for the amount I am going to use it for.

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To use it, simply place the pcb in some kind of jig to hold it in place, and place the stencil on top, and make sure it is aligned with the solder pads on the PCB. All you need to do after that is to use some kind of spatula to help distribute solder paste over the PCB. The stencil will then allow the paste to only go on the pads that should have it on, and it will also help getting a nice consistent amount on each pad, which will end up making the PCB look a lot more professional after reflow.

First tests

Before doing anything more, I decided to try and just place some components on the pcb, without soldering anything.

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The one I was most worried about was the SD card connector. This was the first component I ever designed myself in Eagle, and the drawing for it was a bit confusing and with some measurements missing. Even when I had gone over the part multiple times, I was still not 100% sure it was right, and with the measurement I had to guess it didn’t make me confident either. But as you can see on the image, all connections on the connector lines up just fine with the solder pads on the PCB.

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The next few things I tried was the RJ11 connectors, relays, and screw terminals, which I also designed myself. The SMD voltage regulator also fit just fine over its pads, and so does the transistors. The flyback diodes for the relays are still in the mail so I haven’t been able to test those yet.

Stay tuned

I will be ordering the last parts I forgot everything about, so the next update about the weather station will most likely be with how much success I had with the stencil, a bit about component placement, reflow soldering with as low a budget as possible, a bit of through hole soldering, and possibly some testing of the board.

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