Founding Day 2017 – OMG’s 7th Anniversary!

We’re going to be celebrating the Omaha Maker Group’s 7th anniversary on Tuesday, August 29th. As has become our custom, the evening will include dinner, dessert and the awarding of the annual Founders’ Prize. In addition, I’ve dug up some photos from long ago, showing not only the old space, but also our current K Street space as it was when we first moved in.

Dinner starts around 6, meeting and awards at 7, and dessert thereafter. Additionally, we’ve come up with a few interesting things for a raffle, so we’ll be drawing for that after dessert. Still TBD, but there might be a special “show and tell” after dark… I still need to check with Garrick for details though 🙂

This is an “open house”-type event, and members are encouraged to bring guests. It’s a great opportunity to invite your Maker-inclined friends, family and co-workers to see our new and improved space and find out what the Omaha Maker Group is all about.

Please RSVP below, indicating whether you’ll attend for dinner, dessert, both or neither. Since food needs to be ordered in advance, please be RSVP’d by August 25th so we have an accurate-ish headcount.

Vacuum Chamber

What happens when you give makers a vacuum pump and a bin full of components to rummage around in? Watch the videos to find out.

Can you think of something interesting to put in a vacuum chamber? Post in the comments below.

Reflow Oven Toaster Build

Surface mount soldering is the way to go for small footprint projects and multiple production runs. However, surface mount components aren’t always the most friendly for a soldering iron setup. Imagine a surgeon trying to operate with bulky leather gloves on and you kind of get the picture for what happens when you try to solder a handful of closely-spaced 0402 or 0603 chip resistors with a soldering iron. Hot air soldering is the solution for these tiny components. With hot air, you basically have two choices, a hot air rework station or a reflow oven.
Kevin wanted to take the next step for his home electronics workshop but didn’t want to go all out and buy an expensive reflow tool that wouldn’t get frequent use. After some Internet research, he decided to go the route of using an old toaster oven, a solid state relay, an Arduino, and a reflow oven shield for his build. Check out the projects wiki for all of the details of his build.

Crystal Chamber PID Tuning

Since I'm trying to use a PID controller to keep the chamber temperatures under control I need to tune the PID parameters. And since this is designed to run for hours at a time, and because I'm crap at PID tuning, getting it right it is very tedious. Also presumably I'll need to tune it differently for different chamber loads. A liter of water is going to behave differently from a 50mL of solvent, so I figure I may need to retune it several times for different uses. So I set it up to dump the parameters so I can visualize the process. Nothing fancy, just CSV out the serial port to a log file, then into Excel so I can see what's going on:
I've run half a dozen trials while I learn how to do PID tuning. That image is from part of the process where I'm looking for a good Kp that doesn't overshoot. After playing with it for a while I decided that I might as well get the rest of the hardware and software done, then play with the fine tuning later.

Crystal Chamber Controller Interface

The code I've been using to run the temperature controller for the crystal chamber so far has been pretty bare, just the core PID loop. I don't have it tuned yet, but it's generally functional, so it's time to start getting it in shape to be an appliance.
A while back I picked up some old IBM modems that were being retired from the modem pool at work. I was hoping maybe I could convince one to speak Bell 202, but that didn't pan out. Anyway, they have nice boxes and the front panel has a set of buttons and an HD44780 LCD controller, so I held on to it:
The box has a nice power cord and switch built in, so I will be able to just stuff everything inside and put a connector on the back for the heater and temp sensor wires. Then I can use different chambers depending on what size I need. I could also run set it up to run multiple chambers, it only takes a couple more pins to run additional chambers, so I suppose I could set up to run about three. Maybe for version 2.
I wired it up for the LiquidCrystal library, plugged it in and away it went. The controller is only good for 8 characters, so I've got it set up to cycle the display through each setting one at a time. Right now, that's the setpoint temp, the current temp, and the number of seconds left in the ramp.
I also noticed that at some heater PWM frequencies the power supply squeals, so I added start and end cycle beepers. When I switch power supplies I'll probably need to add an actual beeper, but this was kinda fun in the meantime.
I also mounted the heater and temp sensor for real:
It's there at the bottom of the image. I used poly tube standoffs to keep the leads from contacting the aluminum tape and to provide a relatively stable mounting to the foam. The temp sensor is in the upper right-hand corner. Previously it was just laying on the floor of the chamber. Keeping it up in the warm air rising off the heater helps the response time, but also makes it clear that there's some pretty strong stratification going on in there. I'm pretty sure I'll need to add a tiny fan to keep the air mixed. I didn't want to do that because of the possibility for vibration to affect the crystals, but if it does end up being necessary I can probably isolation mount it somehow. Or maybe I should use an ionic wind type fan. Every project needs some nice high voltages, right? The next step will be to scare up a new power supply that'll fit into the old modem box and come up with a connector for attaching the chamber.

Crystal Chamber Temperature Controller v0.1b

I cobbled together a simple temp controller to try to get a feel for what it'll take to make one that will work for my temp controlled crystal-growing chamber. For this first iteration I've just got a simple PID-controlled heater, LM75 I2C temp sensor, and a 25W heater element.
For now I'm just running on an Arduino and a crappy bench supply (with a way-too-bright power indicator). For the finished project I'm thinking I will use a Teensy 3.0 as I've got some samples of them that I'd like to do a write-up about. To house the controller I'll be repurposing an old modem that has a front panel with a small LCD and a set of buttons that I can use for menu navigation. I can mount a power supply and all the electronics inside and put a connector on the back that plugs into different chambers. This big chamber will be nice for large beakers, but I'd like to have a smaller one for test tubes. I can put a resistor on the chamber side of the connector so the control box can identify which chamber is connected and select the appropriate PID tuning. I ran this for a few hours to see how it behaves. The 0.5C resolution on the sensor is pretty bad, but overall the results were encouraging. I don't really care much about how it handles large rates of change, since the hot solution will go into a preheated chamber. The main concern will be whether it can hold a stable downward ramp with minor fluctuations outside the chamber. I haven't tested that yet. Next step is to get the heating element mounted so it is stable and out of the way and then test with a beaker of hot water so I can see how well it do temperature ramping. I'm pretty sure I'll need to upgrade to a higher resolution sensor for really long ramps, but for a day or two this 0.5C should be ok if I screw with the PID tuning enough. The PID library has some kind of auto-tune that looks interesting, but I haven't figured out how to use it yet.

Insulated Temperature Controlled Chamber

For my crystal-growing I'd like to have better control over temperature so that I can cool solutions very slowly. I've been using a heavy ceramic dish and a hot water bath for this, but I want to try cooling rates of days or weeks. To achieve that I think I'm going to want heavy insulation, radiant barrier, and probably a small computer-controlled heater element. As a start I'm using 2" pink foam with aluminum tape as radiant barrier on the inside surface:
The foam is rated R-10. I'll put a liter of hot water in this and log the rate of change to get an idea of how much it reduces heat loss over open air. That should give me an idea of how much power I'll need the microcontroller temperature controller to handle.
I'd like to be able to keep it as low as 0.1degC per hour while minimizing fluctuations, but at this point I don't have any idea how challenging that will be.