For the final projects in my electronics class, there are always a lot of different interests. One student wants to create a radar gun based on doppler-radar principles. This is a more complicated project mostly because at microwave (2—12 GHz) the devices in a circuit don’t act like the nice simple components we study with Ohm’s law—everything becomes an antenna or a waveguide or both. That said, there are a lot of scrap electronics around with GHz-range components and in fact we have a whole bin of old demos that were designed to show wave effects of microwaves (micro-waves, not the ovens!). The figure shown here is a modern version of what I found.
Example microwave demonstration apparatus
You may be able to find an old setup on eBay or lying around in a demo room somewhere collecting dust. These are still very usable in their original purpose, but I wanted to go a little further since radar is a very practical application of 10 GHz signals.
We need more planned failure in the college experience.
I couldn’t agree more. I’ve mentioned this before but I am still not satisfied that I have added planned failure in any large-scale way. This quote comes from the Tomorrow’s Professor Msg.#2171 posted Sept. 16, 2013. The main premise of the post—to make college more like a video game—is centered on the idea that learning takes place after failures and to improve learning, we need to add more planned failures. The most important part of these planned failures is that they are low-stakes. In other words, we don’t mean more F’s, we mean more times that the student a) makes a mistake, b) has quick feedback, and c) has another low-stakes attempt. Video games reinforce this style of learning, hence the thesis of the post. In a video game, there is no cost to a mistake other than the time it takes to try again. Why should mastery of an academic concept be different?
I have been teaching with Vernier hardware for at least 10 years, so it is great to see them supporting work on the Arduino platform (another passion of mine). I’ll keep an eye out for the Sparkfun boards this fall, this is a great way to get more sensors available for use in our electronics class projects.
They have a very nice guide to interfacing with their sensors:
And more announcements in the newsletter:
I've had grand plans to build a custom workbench for my research lab, but other projects take up my time and kept it from happening. Then in a moment of desperation while trying to move a desk out of the lab, I realized it could complete our workbench. An aluminum rod for the spool holder and two angle brackets to hold it in place. Grand total, $7.49 and 5 minutes to move and build.
PCB for laser diode protection circuit
Our lab is building our fourth and fifth lasers so I finally got around to documenting some of the process. I’ll be posting related items here in order to share the lore and hopefully help others get to a finished working laser. This installment covers our standard laser protection board . This is a small circuit board that is installed between the laser current supply and the laser diode itself. Specifically, the board is as close to the diode as practical in order to provide maximum protection from voltage spikes, surges, and other nasty stuff. The circuit is pretty simple, a filter reduces noise, three forward diodes will not conduct for normal operation (they won’t conduct until the voltage hits 2.1V which is higher than most laser diode operating voltages). There is also a Schottky diode at reversed polarity to provide fast shorting for spikes of the opposite polarity.
The board is simple, and you could certainly make one on some sort of perfboard, but I went ahead and put together a PCB as an excuse to play with circuits.io — a handy site that combines schematic capture, PCB layout, and board ordering in one online interface.
The PCB and schematic are available for our Laser Diode Protection Circuit, and you can order all the parts from our Mouser Project. You may have many of the parts already, and the board is 100% through-hole so you can hack it to your hearts content.
 Many folks use this circuit, I first saw it in the paper by MacAdam et al., and subsequently in a design specified by Todd Meyrath. Please correct me if I should cite someone else.
420 nm light passes through a diffraction grating after being generated by pumping rubidium vapor with 780 nm and 776 nm light. The pump beam appears very dim near the second order diffraction beam.
The first paper from the Photonics and Quantum Optics Lab at Pacific University appeared today in the American Journal of Physics: Collimated blue light generation in rubidium vapor and [PDF]. Congratulations to my student coauthors and our collaborators at the University of Portland!
This is a fairly straightforward experiment to set up if you already do saturated absorption or other rubidium vapor labs anywhere in your curriculum. We used two external cavity diode lasers (780 nm and 776 nm), a warm rubidium vapor cell, and some additional standard optics. A 420 nm bandpass filter is handy, but not necessary for viewing the generated light.
The results are pretty cool to see, and they illustrate frequency conversion in nonlinear optics. With a (barely visible) near-IR beam going into the vapor cell, you see a bright blue/UV beam coming out… it’s almost magic when you see it for the first time. Of course the power in the blue beam is much lower than in the NIR beam, but we are more sensitive to blue so it looks quite bright.
The photo shown here was taken with an open shutter while I swept a piece of paper along the beam. The camera has an internal IR filter which does artificially dim the IR beam. This isn’t too far off from the correct appearance.