Introduction
This challenge includes two blogs - this introductory blog that introduces me and my experimentation plans and a final blog that documents what was accomplished in the experimentation challenge.
Short Technical Biography - Who am I?
For the first decade of my career I worked for an engineering company where I participated in over 350 projects. We would design and build anything, but there was a heavy emphasis on transportation projects, so I designed electronics and software instrumentation for airplanes, boats, ships, trains, trucks, automobiles and robots. My work included a lot of mobile computing, data acquisition systems, controls systems, sensors and optics. I ended up as the head of the electronics department.
The second decade I worked at Carleton University managing their Science Technology Centre where we built thousands of scientific projects. We designed and built prototypes for entrepreneurs and instrumentation for scientists in biology, chemistry, psychology, physics, engineering and medicine.
The third decade was split between fiber-optics telecom and a start-up engineering company. In the fiber-optics company I was the technical authority for 285 electro-optic products and headed up their optical modules development group. At the engineering start-up (I was the CTO) I designed and delivered over 150 new electronic products in 3 years.
In the fourth decade I have mostly been working for a company that develops and markets counter-terrorism products. Our bomb suits have more wearable electronic systems than pretty much any other application for wearable electronics.
Through the decades I have been granted about 9 patents.
Despite having been a manager for 90% of my career, I always insisted on devoting a significant amount of time to technical tasks and I still greatly enjoy learning about technology and designing things that work.
Here is a diagram of one application I intend to implement for this challenge - because I need to add some color to all this text...
Background for this Experimentation Challenge - Why Participate?
I learned early in my career (the hard way) that temperature is really important in electronics and I have had to deal with all aspects of temperature effects and control throughout my career. The components in this challenge include technology I have not used before, so I am keen to learn how well they work and what they are good for. Part of this project will be involved in testing performance of the thermal switches in the kit and discussing the technology and applications for the components. To help with this I have several sources of heat such as heat guns, heater cores, nichrome wire, electric heaters etc. and I have several temperature measurement devices including thermocouples, semiconductor temperature sensors and IR thermal gun. The component test plan will investigate thermal response time, switching time, thermal hysteresis, on and off impedance, impedance during switching, switch bounce and self heating.
What do I want to do with thermal switches?
Another part of this challenge will be using thermal switches in an actual application.
I always like to design and build something when I do element14 contests and this time I want to build a cosy cat house. This is all about temperature control so it is a great opportunity to use some of the devices in the Kemet kit.
We have a cat who likes to spend time outside watching the world go by, but we don't let her out to roam the neighborhood killing birds. She is happy to be out there on a leash, however Canadian winters can be very cold, right now it is about -30C outside. She still wants to go out, but doesn't stay out very long when it is this cold. This little cat house is an experiment to see if she likes to hang out in her own little temperature controlled house, open at one end.
The challenge for me is to ensure the system is safe and presents no danger in the event of a system failure. Of course the cat house will be over-designed and include all kinds of interlocks, control systems and monitoring instrumentation. It doesn't need to keep the house very hot - the cat seems very comfortable down to minus ten Celcius. You can get some idea of what is in the project from the diagram above but to find out just how overboard it is going to be you will have to read the next blog.
What else do I want to do with thermal switches?
I also have a pressing need to solve a problem I have will all 3D printers. Actually it is a problem with PLA filament, which is what I always use. It seems that PLA is wound on reels when it is still warm and flexible and it cures in this curled shape. When feeding it into a printer, the filament must be straitened out of the curled shape it hardened in. The straitening process induces stress in the filament, but the filament can usually bend this much without breaking. However, if the filament is left in the printer, the continued stress of being held in an unnatural shape eventually causes the filament to break, usually in about one day. This means the filament either needs to be cleaned out of the printer after it breaks, which is wasteful and time consuming, or the filament must be removed from the printer whenever it could sit idle for a half a day. This is problematic if you are not nearby or asleep when the print completes. Even if you get there 10 minutes too late, the printer needs to be re-heated to get the filament out. Some filament is so brittle, it breaks in the middle of a print, so I really want to solve the problem.
To tackle this problem, I will try to anneal the filament as it comes off the spool, which hopefully will lower the stress of it taking on a new shape and allow the filament to stay in the printer between prints. To do this I need a temperature controlled heater. The simplest solution would be to use one of the Kemet thermal switches to act as a thermostat, however I will start by using one of the switches as a safety cutoff in case the heater gets too hot. If it melts the filament it could create quite a mess to clean out of the printer. If this technique works it will definitely see a lot of use and it will save me a lot of aggravation.
Here is a diagram outlining what is involved in this system:
The filament coming off the spool will pass slowly through a heated copper tube which is controlled to be at a temperature between the glass transition temperature and the melting temperature. Hopefully it comes out of the copper tube in a less curly and less stressed condition. It isn't clear that this will work, but it is a perfect candidate for an experimentation challenge.
Project Status
- It looks like the revised kit is supposed to have 11 switches in it and the IR thermometer was dropped.
- I received 22 thermal switches and indeed there was no IR thermometer.
- Fortunately I already have an IR thermometer so this doesn't present an obstacle to my tests.
- I have been collecting test apparatus and materials to build the two big applications for thermal switches.
- One temperature controller (thermostat) has arrived, the other one is still in transit
- I have a voltmeter/ammeter module for the cat house heater and a breaker
- I have a thermal pad heater for the cat house and some materials to build the exterior shell
- I have copper tubing and some resistor "heaters" for the filament annealer
- I have a power supply for each system
Blog 1 Conclusions
I expect to come away from this project having learned about Kemet thermal switches and how to apply them to my applications. Both applications are also of significant interest to me, and I plan to have fun implementing them.
Relevant Links
/challenges-projects/design-challenges/experimenting-with-thermal-switches/
