PCB Assembly

I've designed a PCB for this project and had some made by Aisler (who runs the PCB fabrication for Fritzing now). They make good boards and are a great group of people to deal with.

You can order boards or a full kit directly from Aisler.

Getting started

Here are all the needed pieces, including cut-to-size pieces of header.

Step 1: The proximity breakout header

This will probably be a bit different than the way you've connected (or will connect) most breakouts. As shown in the prototype page, the proximity sensor is at a right angle to the board. In the final PCB assembly I've used a piece of right angle header to accomplish this.

The bent pins go through the board. There's a problem, though. If you look at the board, the Neopixel strip covers the spot where the header pins come though the board. My approach was to trim those pins to be more or less flush with the board.

Now they don't protrude. Soldering is much as usual. Just be sure to heat the pin, a little more attention is required since it isn't sticking through the board. Solder will wick into the plated hole and, as long as you don't put on too much solder, will make a nice flush connection.  As usual, I solder one pin to tack it in place, then melt that joint and tweak the positions, angle, etc of the header. Once it's how it should be, I solder the rest of the pins.

Step 2: The Neopixel strip

This is also a bit different. The Neopixel strips have solder pads on either end. The PCB has matching solder pads. The different thing we're going to do here is not using wires or headers to connect them.

Start by tinning the pads on the PCB with a generous amount of solder.

No, I mean it. Be quite generous.

Next, do the same thing on the pads of the Neopixel strip.

Now the tricky bit. While holding the strip in place against the PCB, solder pad to matching solder pad. Heat one with your iron. Be careful as it will have a tendency to slip such that the pads are not lined up; they'll end up staggered. So hold them together gently. 

The goal is to melt the solder blobs on the matching pair of pads simultaneously so that they flow together. Let them cool and you will have a nice connection.

My advice is to do a pair of pads on one end of the strip. Then do a pair of the opposite end. One pad is far easier to redo than several. When you're done, have a close look to verify that the solder on matching pads has, indeed, flowed together. If not, reheat them, adding a bit more solder if necessary. Be careful not to overdo it, though..

Below, you can see the four pairs of pads at one end of the strip nicely connected.

The strip won't be sitting flush on the PCB, but that's fine.All that's required is a solid connection on those eight pairs of pads.

This is why we trimmed the header pins: it lets the strip sit as close as it can to the board.  This is also why we started with that header.

Step 3: Power

Next, add the components to the power supply section of the board. This includes the power jack, the 7805 5v regulator, and 10uF (C3), 100uF (C2), & 100nF (C4) capacitors. What happened to C1?  I have no idea... bitten by Fritzing auto-numbering.

Note that the two larger capacitors are polarized and need to be mounting with the negative leads facing each other. These are well marked, often with a stripe. Similarly the regulator has to go the right way round. The metal heatsink is shown on the board. See the photo below.

Step 4: The Trinket

Attach the bits of straight header to the Trinket and place it on the board. If you haven't done this sort of thing before, have a look in the Feather M0 Express tutorial for advice/instruction. It's the same for the Trinket, the only different is the exact position and size of the header strips.

Flip the board over and solder the Trinket's pins. Again, I always start with one and make sure everything is how it should be. Then I do the opposite corner, making sure the entire thing is right. Then I do the rest of the pins.

Whether you trim the pins is up to you. My though is to design a printable case for this at some point, so I trimmed the pins so they won't be in the way.

Just a note: I keep an older pair of side cutters for this. The blade alignment is a bit off and I replaced them a while ago with a more expensive pair. I keep my good pair for cutting fine wire (30 or 24 gauge usually) and use the older pair for rougher work. Trimming header pins classifies as rougher work. So as you replace and/or upgrade your tools, hold onto the old ones unless they are broken.

Step 5: The proximity sensor

The final step is mounting the VL53L0X breakout on the header strip we started out with.

Slide the breakout on the header pins, solder one pin, adjust the breakout (you want a nice 90 degree angle with the PCB) and solder up the rest.

Once again, trim the excess pin length if you wish.

That's it. Time to load the CircuitPython runtime, libraries, and code.py.

This guide was first published on Jun 13, 2018. It was last updated on Jun 13, 2018. This page (PCB Assembly) was last updated on Jul 09, 2018.