After designing the circuit board, I thought I would get back to glassing but nothing got done on that end before all the components and the circuit boards arrived.

I’ve soldered surface-mount boards before using the “smear flux everywhere and touch the pins with the solder iron” method, which works but is pretty slow and error prone. I decided to up my game by also ordering a hot-air reword station. This is basically a small hot-air gun that can accurately control the temperature and airflow. This allows you to heat up the board and components enough to melt solder. By applying solder paste (which is solder in non-metallic form which turns into metal when heated up) to the pads, sticking the components into the paste, and then heating everything up until the solder melts and flows into the joint, you can make quite good-looking boards, and the risk of bridging pins is smaller than when using the solder iron.

The solder paste is squirted out with a tiny syringe (the real way of doing it is to make a solder mask, which is a sheet of plastic or metal with holes where the pads are, so you can just smear paste across the entire board in one fell swoop, but it doesn’t really make sense making one of those for a single board) which took some practice. Especially on the small IC pads that are very close together, you can add too much paste and end up bridging the pins anyway. Once I got the hang of it, though, this was a pretty painless way of doing it.

Step one was to ensure I could get the small-pin chips soldered. This is the Atmega328 and a few of the passive components.

I started with the hardest part, the Atmega328 32-pin package, since I didn’t want to do a bunch of other work and then screw that one up. My first attempt looked a bit uncertain, when I probed the pins there appeared to be an invisible bridge between two of them. To be on the safe side, I melted it off and started over.

Once I was done with the chips, there was just a loooong list of capacitors and resistors, with a few diodes and transistors in there. It took a while to make sure I got the right component values on all the places, but after a few hours it was done.

All components and connectors mounted, ready for testing.

With all the components mounted, it was time to try to flash the Atmega328 with the wireless boot loader and set the fuses accordingly. No joy. I was wondering whether I had overheated the chip when soldering, because all the connections checked out, until I noted that I had flipped a diode. With that fixed, I got the chip flashed correctly.

Then I had to program the Xbee with the correct settings to connect to my mesh network. The requirement to be able to connect both the Atmega or the Xbee to the serial line for programming took some thinking. Furthermore, the Xbee is strictly 3.3V while the Arduino TinyUSB programmer supplies 5V. This means the power to the Xbee and the Arduino needed to be isolated, as well as the serial lines.

The solution I came up with uses logic-level converter circuits. There is an ingenious bi-directional level converter circuit that uses a single FET and a few resistors. These convert between two voltage levels and will also block signals if one of the two supply voltages are zero, so by adding two of these converters between the serial ports on the Atmega and the Xbee, with a header in between, and a jumper that determines whether the header powers the Atmega or XBee, we get all the desired features: There is no back-powering between the Atmega and XBee power circuits or over the serial pins, but when powered through the onboard voltage regulator they can communicate over the serial lines.

Finally it was time to power the 12V in and see if everything worked, which it did. Almost. One of the LEDs hooked up to the XBee didn’t work, which turned out to be another flipped diode, easily fixed.

The board powered up for testing. The two red LEDs at the bottom indicate when the heater and the thermoelectric cooler are on, respectively. The red LED in the center is the 12V power indication, the yellow at the top the Xbee association light, and the green in the upper left shows the XBee RSSI (radio received power). There are two more LEDS there that show traffic on the serial send/receive lines.

Everything works so far in that the heater and cooler output LEDs blink when turned on and off, and I can talk to the board over the XBee. I haven’t attempted to hook up any of the peripherals yet, though.

Now I really need to get back to glassing so I can assemble the box and start wiring things up.

Lately, the glass work on the physical box has been on pause since I realized I needed to work out what the connections to all the sensors is going to look like. To work out the electronics, I buckled down and started designing the circuit board. I had a vague notion of what it needed to do but it always helps flesh out the design when you really have to put it down on a board.

Previously, I’ve designed my boards in Eagle, which I bought back in 2010 or so. However, since then Eagle has been assimilated by Autodesk and its functionality is now part of Fusion 360. Strangely enough, while Fusion 360 has no limits on its capabilities for 3D design even in the free version, the electronics design retains a limit on the board size from the free version of Eagle. I can’t use my old Eagle license and Autodesk has now taken the standalone Eagle entirely to a subscription model which I wasn’t about to sign up for. Luckily I could, barely, fit all the stuff I needed within the board size limit in Fusion 360 (I think it’s 80cm^2.)

While the Fusion 360 Electronics experience feels like the 3D design experience from 4 years ago in that it crashes constantly, the integration is pretty cool. It automatically creates a 3D model of your circuit board that you can integrate into the 3D design. I haven’t made use of this yet but I will 3D-print the enclosure for the electronics so it will come in handy there. This way there’s no question of whether the board will fit and you can even make very funky board shapes if you need to squeeze the board in somewhere.

Designing the schematic is very slow for me, since I do this rarely enough that I basically have to look everything up all the time, but I just put in the order at OshPark so in a couple weeks I should hopefully have the board here.

A rendering of the circuit board from Fusion 360. Not all components have 3D models, so the connectors and some of the components just show up as squares.

Now that I know exactly how things will be hooked up, I can get back to putting the box together with routings for the wires.

After glassing the cover for the dehumidification channel, I needed to mount the thermoelectric cooler. Small tasks are best now….

This is the cold side of the thermoelectric cooler. This cold sink protrudes into the channel in the opposing part, forcing the air over it.

The hole fit pretty well, there’s a bit of clearance but I’ll seal this up with some silicone when mounting the cooler for real.

On the outside, I had to drill and tap the holes in the hardpoints.

This is the hot side of the thermoelectric cooler. This will also need a fan. The wine cooler I stole it from has a slanted fan mounted under it, I’ll have to do something similar.

I marked the locations of the holes by trial fitting the thermoelectric element and managed to drill and tap pretty accurately.

The thermoelectric cooler, now mounted with screws.

I’ll also need some sort of guide so the cover can be positively located in the correct position, and then some latch or something to hold it in place. I have some 8mm guide pins that are left over from the EFI project (I was going to use them for the throttle linkage) that I’m going to use. That’ll be next post.

I’ve been distracted by things like trying to find toilet paper (seriously, people) but I’ve been trying to make a little progress on the filament storage box.

Since the last post, I mounted the fan that will push air over the cold plate for dehumidification. It fit pretty well in the hole I made, but when glassing the sides I did get some crap on the fiberglass flanges so I had to pull out the Dremel to get it to lie flat.

The dehumidifier fan in its slot. I still need to make a passthrough for the wires. (Not just for the fan but also for the temperature/humidity sensors that will be mounted before and after the cold plate.)

I also discovered that, when I trimmed the fiberglass flange, I unfortunately cut it a bit tight. Two of the fan mounting holes only make a half hole in the fiberglass. I’m sure it’ll be fine, but note to self is that it’s better to leave too much and have to grind it down than to knife trim too close…

The fan for the dehumidification circuit. This is just a temporary mounting, it won’t get screwed in place until the box sides have been joined.

I was going to join the sides of the box together, but that seemed like a big job that will need a lot of free time, so instead I prepared the cover for the dehumidification circuit for glassing on the outer side. I’d already done the inner side, which is a simple flat layup. The outer side, however, needed hardpoints for the fairly large and heavy heatsink for the thermoelectric cooler.

To avoid having to glass the edges separately, I also rounded the corners on the outer side so I could just let the fiberglass cloth flow onto the edges and make a corner with the inner side. This did make the layup itself more complicated since now the cloth had to be cut and overlapped in the outer corners as well as in the inner corners of the hole for the thermoelectric element.

The outer side of the cover for the dehumidification circuit. The hole is for the thermoelectric cooler, and the shallow depression on the lower left side of the hole is for the wire bundle coming out of it. The entire part is covered with peel ply on all sides since I used many scrap pieces of BID cloth leaving many joints.

It took a while but turned out OK. I got the glass to lie down pretty well around the corners but there are so many joins since I used scrap pieces that I thought it best to peel ply the entire face so the joints don’t have sharp glass edges. There may still be some in the corners where I had to cut the cloth, but that’s easily taken down once it’s cure.

This was the first time I unpacked my full roll of peel ply cloth (as opposed to the 2″ wide tape I’ve been using before. It was a bit wrinkly, which might be reflected in the surface once I pull it off. If it’s too bad I guess I can sand it.

Next task on the list is probably to assemble the box, but separately I’ve started thinking about the circuit diagram. It’s cool that Eagle, the circuit diagram editor that I’ve been using since 2012, now is integrated into Fusion 360, so not only can you design your circuit board in Fusion, you also then get a 3D model of the board so you can fit it into the rest of the design.

More progress on the filament storage box. All 5 sides of the box have been glassed on at least one side, and the dehumidifier circuit side was completed.

The left and right sides of the box have been glassed. The left side has the channels for the air to blow over the cold plate, which made a bit more complicated glasswork than the flat sides I’ve done so far.

The layups for the air channel were a bit tricky compared to the flat sides I’ve done so far. Instead of just wetting out rectangular pieces of cloth, this has numerous corners and edges. The inside of the channel only has a single ply of bidirectional cloth, which is very flexible. When you lay it down so the fibers run at 45-degree angles to the corners, it takes a very small radius, especially on these inside corners where the adhesion to the sides hold it in. I used random scrap cloth pieces and cut them as I went, and amazingly it did not turn out terrible. I’ve verified that both the fan and the cold plate for the thermoelectric element fits.

Closeup of the hole in the side of the box where the 60mm fan will be mounted that blows air over the cold plate to condense water out of the air.

The next step will be to attach the sides of the box, but before doing that I wanted to mount the large aluminum plate to which the old silicone 3d printer heater was going to be fixed. On the TAZ6 this is affixed to the back of the glass printer bed, so I got some sheets of the same adhesive (3M 468MP) and stuck it to a 1/8″ thick aluminum plate I cut out. The aluminum plate is mounted with M3 screws to threads cut into the aluminum hardpoints I mounted into the foam before glassing the back of the box, see the last post.

1/8″ 6061 plate with the old TAZ6 print bed silicone heater attached to the back side.

In the last post, I described the basic idea of the dehumidified filament storage box. I don’t have a lot of time to work on it, so progress is slow, but I’ve done a few layups.

The layup on the inside of the back section of the box. This side has these aluminum hard points, that will be drilled and threaded to hold the hot plate.

The back side is made from 2″  foam to give good insulation against the hot plate and maximum rigidity. That part has been glassed on both sides. I floxed 4 aluminum hard points on the inside so the heater plate can be attached.

A closeup of one of the aluminum hardpoints. They’re made of 1/4″ 6061 floxed in place under the glass.

The right side of the box, where the fan and the cold plate for the dehumidifier is mounted, is partly completed.

The right side of the box, with an outline of the dehumidification passage. The fan sits in the upper left, then the cold plate will go below it, mounted on the top. The passage has a bottom collection point where the condensate will gather and run out, and then the air circulates back up and re-enters the box through the hole in the upper right.

Here the foam has been routed out for the air passage, and the surface glassed. The passage itself will be glassed separately once the surface has cured. There are a lot of corners here so it will be pretty tedious to do.

I started using West System epoxy, which is what I’ve used exclusively for glass work since I bought it back in 2012. However, since the inside of this box will be quite warm, well above the heat deflection temperature of the West System, I decided it would be a good idea to pull out the Pro-Set that I got way back before we moved from L.A. If post-cured, it has a much higher heat deflection temperature up towards 80-100C, so it seems a better choice. It’s not like I’m using it for anything else, anyway.

I was a little bit worried that it would no longer be good, since it’s specified with a shelf life of 2 years, but I mixed a test batch and it cured fine. The hardener has turned very brown, much more so than the West hardener, even though it’s been in sealed containers, but it doesn’t seem to affect the cure.

However, I have been getting a sticky, oil-like layer on top of the cured expoxy, especially the stuff that remains in the cup. I assume this is what’s known as “amine blush”, a byproduct of the hardener reacting with moisture. I’ve never noticed it with West System, but the Pro-Set instructions warn that it’s possible. The high humidity here (I’m working in the garage, too) probably doesn’t help. Maybe I should be doing the layups in the dehumidified room…

As you may remember, my 3D printer is mostly used with Nylon or polycarbonate filaments, since those are strong and works to high temperatures. Unfortunately they’re also very hygroscopic, so they absorb moisture from the air (which we have a lot of here) and then you can’t really print with them without getting blobs and oozing everywhere. You can literally see steam coming out of the nozzle when printing if the filament’s been sitting out.

To fix this you have to dry it before printing, and then keep it dry. I’ve been doing this by keeping the filaments in the oven at ~80C for a day and then storing them in air-tight tupperwares along with boxes of dessicant. This makes it doable, but isn’t really cutting it in the long run.

First, drying a full spool doesn’t actually dry it all, the inner part must not get enough airflow so even after a day it’s not sufficiently dry to print. Since I often print large objects that use the better part of an entire spool, this means that at some point during the print things will start going south as you get into the un-dried part of the filament.

Second, the “air-tight” containers aren’t, and even if they were you have to open them and put the spool into the little box on the printer I feed it from. This means the dessicants get saturated, even though I have about a pound in there. You can dry them, but that gets old, too.

The net effect of this is that I basically don’t print stuff unless I have a big project that warrants baking filaments and dessicants. These days time is a sparse commodity so streamlining this would do wonders for being able to use the printer as an everyday tool.

So here’s the plan:

I’m going to build a large, insulated box where I can store several spools of the filaments I use most often. This box will have a heater that can heat the entire box to 80C to bake the moisture out of the filaments. It will also have a dehumidifier, essentially a cold plate where the moisture in the air will condense and then leave the box. The box will have outlets with teflon tubing where the filament will feed directly into the printer. The tubing for filaments that aren’t used can be stuck back into the box to seal those holes. This way, filaments will be continuously baked and kept dry.

A rendering of the filament storage box in Fusion 360. The square in the back is the heating plate, the holes on the right for the dehumidifier.

For making the box, I will make use of some of the foam and fiberglass I have for the on-indefinite-hold Long-Ez build. The heater will be the old heater plate for the 3D printer, which is capable for 360W at 24V. The dehumidifier will re-use the thermo-electric cooler from the long-defunct Wine fridge (see the first ever post on this blog!) 

An internal fan will circulate the air internally, and on one side of the box another fan will blow air into a passage that contains the cold sink of the thermoelectric cooler and then comes back out into the box.

Finding fans that are OK with being put into an 80C environment is a bit tricky but Mouser has a few. The humidity and temperature in the box and after the cold plate will be monitored with the same kind of sensors that I use for the weather station. Controlling it all will be, of course, an Arduino.

Both software and hardware-wise, I already have most of what will be needed for this project, since the functionality is some mix of the weather station and the epoxy hot box. I did need to buy the fans and a power supply (for the 12V thermoelectric cooler and fans, for the 24V I’m reusing the one from the 3d printer.)

Sorry for this wall of text, but I wanted to give an outline of what I’m going to do. I’ve started making some parts, so hopefully I can give a first progress update soon.