Solder paste is a little tricky to handle, because most solder paste needs to be refrigerated at 32-50°F to maintain it’s shelf life. Stored at room temp, it tends to get tacky and dry out within a few weeks. Solder paste is also toxic (it contains lead among other things) so it’s not something you want to put in the fridge with your meatloaf.
I had an old beer cooler sitting in the garage that Kylie picked up on the street a while back. It uses a Peltier thermoelectric cooler to cool the inside and can achieve sub-freezing temperatures.
Since I didn’t want to leave the cooler on constantly, and below freezing is actually too cold for solder paste, I decided to add a PID controller to the cooler to create a solder paste fridge for the garage. To do this, I needed the following items:
Love Controls 16A PID Controller found at a surplus store. This one happens to run on 12V and also has a 15V output which made things simple, but other configurations are possible and almost any PID controller should work provided it supports “direct” mode (for cooling instead of heating) and has a relay or switched voltage output.
K-type thermocouple to measure the inside temperature of the cooler
power MOSFET capable of switching 12V @ at least 5A, lower on-resistance is better.
1k bleed resistor to ensure the MOSFET turns off when it’s supposed to
a small heatsink for the MOSFET (may be unnecessary, mine doesn’t even get warm)
Since the PID controller happens to run on 12V I was able to use the existing 12V power supply for the cooler to power everything. I configured it so that if the desired temperature is below the current temperature, the PID controller turns on the MOSFET which supplies power to the Peltier cooler and it’s associated fans.
The only hangup I had was that at first I didn’t place the 1k resistor across the output of the controller, and the cooler would stay on constantly. It turns out that because MOSFETs have almost no gate current, once the PID controller turned off it’s 15V output, the gate of the FET would continue to float high. The bleed resistor to ground ensures that this can’t happen, and the FET turns off properly.
Here’s a picture of the finished solder paste fridge complete with PID controller (click for a larger version).
“Wiring harnesses are an essential and often overlooked part of any electrical system. On a car, a good wiring harness can make the difference between a weekend joyride and a long tow home. Building a quality wiring harness requires a couple inexpensive tools and the right techniques…”
The Maker Faire is an event held twice a year (alternating between San Mateo, California and Austin, Texas) by the folks at Make Magazine, one of my favorite publications from O’Reilly. The event centers on DIY culture, covering everything from making combat robots to felting and needlepoint.
During the Maker Faire I handed out a one page tutorial with information about where to buy the tools and supplies as well as the steps needed to create a template and make a wiring harness from scratch.
This past weekend, I attended The Last HOPE at the Hotel Pennsylvania in NYC. The con was awesome and I had a great time. This was my first HOPE, and I noticed a few strong themes this year, including:
Hardware hacking is getting a lot of attention and there is a lot of interest in microcontrollers including new design and reverse engineering off the shelf hardware like RFID.
Local community based physical spaces for hacking are booming. Hackerspaces like NYC Resistor and the Hacktory are becoming a very big part of the scene, and new hackerspaces are popping up all over the world. Each space has their own unique interests, but common themes seem to be microcontroller hacking (especially Arduino), fabrication (like Reprap and Fab@Home) and other more physical projects instead of just writing code. There was even a new wiki announced at the show that is devoted to tracking hackerspaces and helping start new ones at hackerspaces.org.
There was an awesome talk about Biohacking by Chris Seidel (I wish I could find a link) that makes me wonder if we will see more of this in the future as Bioengineering becomes more accessible to the masses. The parallels Chris identified between biological processes and electrical circuits were spooky.
Last Monday I went on a surplus run in the South Bay.
This was a common pastime for myself and a few especially geeky friends around 1994-2002. After that, eBay and mail order electronics pretty much took over, forcing the most interesting surplus electronics stores in Silicon Valley (ie. RA Enterprises) to close their doors. With the news that HSC Electronics is moving to an undisclosed location and Triangle Machine is going out of business, I was starting to worry that the days of finding cheap, local electronics surplus were over.
However, thanks to this guide I discovered a few new surplus goldmines:
Excess Solutions in Milpitas (their site is here) – lots of mechanical parts, connectors, as well as ICs and components.
So maybe electronics surplus is still alive in Silicon Valley. Both stores are a bit of a drive from the city, but both are still open to foot traffic and appear to have almost every component you could possibly need for an electronics project. What I did find lacking at both locations was cheap surplus equipment. One of the most rewarding things for me in the past has been taking apart mysterious equipment to collect interesting bits and pieces for my junk box. Triangle Machine still has some, but may only be around through the end of August. Regardless, I will definitely be making the trip back to the South Bay for some electronics scrounging soon, whether HSC sticks around or not.