All posts by Steve Dickie

On to light – More sneaky uses for free software

We started light this week in my physics class. I do a set of labs using CBLs (from TI) with the TI83/84 graphing calculators. We look at bulb wattage vs. brightness and distance vs. intensity (finding an inverse square relationship). I also have students see the fluctuations in a regular light bulb just caused by alternating current.

For those peope out there who don’t have CBL’s, LabPro’s, or PASCO probeware all you need to do these labs is a cheap solar cell and a computer running Audacity and/or Visual Analyzer. You’ll also need a 3.5 mm headphone jack. You can pick this up at Radioshack or you can go to the dollar store and pick up a cheap set of headphones.

Headphones will typically be stereo so there will be two leads, one for each ear. You only need one ear’s worth of wire. When you strip the lead you will find two wires, solder one wire to each of the leads on the solar cell. Then simply plug it into the microphone jack on your computer and load up Visual Analyzer. Point the cell at a light and see the 60 Hz alternating current (shows up as the light turns on and off 120 times a second).

You can use this to determine relative intensity, but to get exact lumens or lux you’ll have to find a way to calibrate your probe. You’ll need a volt meter for this. You can find them for under $10 if you look around a bit (assuming you don’t have any already).

The solar cell will also pick up infrared light. Just point a remote control at the cell and record in Audacity, zoom in to see how the pattern is different for different buttons and different remotes.

For under $5 you can have a very versitle light probe suitable for a number of great labs or demos.

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Teaching Sound

I’m finally up to teaching sound in my physics classes. This week we did a number of sound related labs/activities. One was determining the speed of sound using a long tube and a flat surface.

The tube (1.5 – 2 m) is stood up on a hard surface (tile floor). Using Audacity you can record a snap at the top of the tube and the echo of the snap off the floor. It’s really quite cool. Once you zoom in quite a bit it looks something like this. I’ve written up fairly comprehensive instructions. If you have any questions or need further clarifications feel free to respond to this post.

Audacity Echo.pdf (Sorry, my link is broken. I’ll fix the link to the document soon. Just drop me an email and I’ll send you the directions)

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New Version of Visual Analyzer

I’ve talked about Visual Analyzer in the past as being a great free oscilloscope/function generator program. The author has recently released another new version. He has also created an English language website. The previous site was in Italian and used frames. Someone told me the Italian site doesn’t work if you use Safari (Macintosh web browser). The English site is a very simple site with no frames.

Visual Analyzer can be downloaded from:

New Stuff in the new version and/or new stuff I’ve discovered that may have been in the previous version:

  • “Peak Hold” in the spectrum window. There is a check box in the spectrum window that will capture the peak frequencies. This is really helpful for sounds that are of very shot durations.
  • X-Y Graph: You can do an X-Y graph of the right and left channels. It’s been too long since I’ve used an actual oscilloscope to remember why you might want to do this.
  • My desktop computer had problems with VA 7.0. I have an Intel motherboard with an integrated sound card. VA 7.0 did no like this and I was only able to use the microphone as my input device. VA 8 has resolved this problem.

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Visual Analyzer

My favorite free oscilloscope program just got better. I’ve mentioned it before and I’m sure I’ll be mentioning again some time in the future. Visual Analyzer is free and has been upgraded so if you’ve already got it you should probably download it again. The site is in Italian, just look in the top left corner of the browser window and click “Download VA 7.0.5”

The coolest new feature is the ability to create sounds composed of multiple waves of different frequencies and intensities. Why would you do this? Picture playing a sound from a musical instrument into the scope. Capture the different harmonics the instrument creates and then use VA to simulate the same sound. With each harmonic you add the sound made by the program should get closer and closer to the original.

I did have a problem with the new version though. There may be a conflict with my sound card. I’m going to run it by a computer nerd friend of mine to see if we can get it figured out. On my slightly older computer it ran without a hitch.


Sorry I didn’t write about my sound demos last week. The end of the school year is just too busy. Here’s the basic list:

I used the function generator to show interference, both constructive and destructive by setting each speaker to a slightly different frequency. You can create some really good beats. When you feed the signal in to Visual Analyzer (VA) you can see the beats as well.

I illustrated destructive interference by setting both speakers to the same frequency and pointing them at my microphone. I slowly changed the distance to the microphone of one of them until the o-scope showed nearly complete destructive interference. If you were ambitious you could use this to determine the wavelength of the sound as well.

Using VA’s function generator I generated a frequency tuned to a graduated cylinder to cause it to resonate. I used a cheap $0.50 speaker that was to quite to hear until it was brought near the graduate. You could use this to determine the speed of sound if you were so inclined.

I used a variety of musical instruments to show the different numbers and strengths of relative harmonics using the FFT in VA to illustrate why different instruments sound different even when playing the same note.

Teaching Sound

Sorry I haven’t posted in a couple of weeks. I’ve been a bit busy and haven’t really stumbled across anything new and cool in educational technology.

For the next week or so I’ll be teaching sound in my freshman physical science course. I use an oscilloscope program on my computer to do this. I’ve seen several different programs for doing this and most of them cost a lot of money. The one I use is free and from the descriptions I’ve read of the costly ones it is better.

I use Visual Analyzer. The download site is in Italian but all you need to do is click on Download VA near the upper left. For those interested I’ve also created some simple instructions on how to Use VA. Over the course of this week I’ll post how I’m using VA to teach sound.