DIY Oscilloscope with a Scanning Laser

If you’ve ever used an old-school analog oscilloscope (an experience everyone should have!) you probably noticed that the trace is simply drawn by a beam that scans across the CRT at a constant rate, creating a straight line when there’s no signal. The input signal simply affects the y-component of the beam, deflecting it into the shape of your waveform. [Steve] wrote in to let us know about his home-built “oscilloscope” that works a lot like a simple analog oscilloscope, albeit with a laser instead of  a CRT.

[Steve]’s scope is built out of a hodgepodge of parts including Lego, an Erector set, LittleBits, and a Kano Computer (based on a Raspberry Pi). The Pi generates a PWM signal that controls the speed of a LittleBits motor. The motor is hooked up to a spinning mirror that sweeps the laser across some graph paper, creating a straight laser line.

After he got his sweep working, [Steve] took a small speaker and mounted a mirror to its cone. Next he mounted the speaker so the laser’s beam hits the mirror on the speaker, the spinning sweep mirror, and finally the graph paper display. The scope’s input signal (in this case, audio from a phone) is fed into the speaker which deflects the laser beam up and down as it is swept across the paper, forming a nice oscilloscope-like trace.

While [Steve]’s scope might not be incredibly usable in most cases, it’s still a great proof of concept and a good way to learn how old oscilloscopes work. Check out the video after the break to see the laser scope in action.

20 thoughts on “DIY Oscilloscope with a Scanning Laser

  1. More of a waveform visualizer than an oscilloscope. The most important part of an Oscope is being able to measure voltages as well as frequency. Calibration is the key.

    1. If he knows the scanning rate, he can determine frequency the same way we always have before scopes came on the scene that would do the measuring for us. The same is true with the voltage, so long as the ratio of volts per division is a known quantity, something that could be easily determined. I suspect that this is why he used graph paper as a background medium.

      This is as much a true oscilloscope as any of the analog Tektronics scopes that I have owned over the years. Kudos to [Steve] for an excellent build, and extra credit for incorporating Lego. :)

  2. What an incredibly complex way to do a simple task! A 32-bit computer with 512 MB of RAM and a multitasking operating system does nothing but blink an LED, which through an optocoupler and amplifier, drives a motor. This much could be done with a battery, a variable resistor, and a motor. And he didn’t just use a $30 Raspberry Pi, he used a $150 kit that includes an RPi for this task, in addition to at least $100 for Little Bits kit.

    But all of that aside, I don’t understand why [Ethan Zonka] refers to this project as a “home-built ‘oscilloscope’ that works a lot like a simple analog oscilloscope”, when it IS in fact an analog oscilloscope, by pretty much any reasonable definition of ‘oscilloscope’.

  3. I don’t really get that speaker thing. Isn’t the mirror on the speaker supposed to be tilted up/down a bit in order to reflect laser to different positions on y-asix on the screen? Since the speaker can only push-out or pull-in the mirror linearly, how could the laser be reflected vertically?

    1. It works because it’s attached off it’s center of mass, so the linear motion causes it to twist. But you’re right, you’d get a much better signal if you fixed one side as a hinge. (Tape works great IIRC)

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