"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."
One of the commentators pointed out:
"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’."
Yes, it is expensively over-engineered. The actual point of this build was to demonstrate optocoupling (I got tired of building magnetic stirrers and wanted to try something completely different). There are much simpler ways to demonstrate optocoupling, but how often does one get the chance to build an analog oscilloscope out of a disparate pile of toys, however Rube Goldberg-esque, just for fun?
In my previous project "An Experiment to Combine Lego and Snap Circuits" I designed a simple Snap Circuits circuit to spin a mirror and in this project I'm revisiting the Laser oscilloscope proof of concept with a lot fewer parts.
Build the graph paper target
The graph paper screen is easy to build with a piece of cardboard, graph paper, and a large binder clip:
I used a magnetic chip clip to clamp the laser pointer switch (a press switch) in the on position and attach the laser pointer to the Erector set mount. Unfortunately, there are plastic grips on the chip clip that interfere with the smooth rotation of the chip clip against the Erector set strip. So, I added a neodymium magnet from a magnetic keychain that I took apart and the keychain magnet lets me smoothly rotate the chip clip.
Magnetic chip clip
(Optional) neodymium magnet
Erector Set Parts:
1 Strip, 1 1/2", 15 hole
1 Base plate, seven hole by five hole
2 Triangle brackets
4 Small bolts
2 Medium bolts
1 Hex wrench
Erector set right angle bracket 3-hole (mine is a bit more than 90°)
Erector set nut
Computer case thumbscrew
I used a knife to cut a slit in the rubber grip of the chip clip just wide enough for the Erector set angle bracket to fit tightly once inserted in the grip.
Attach the chip clip to the Erector set stand with the Erector set nut and computer case thubmscrew.
Mount the Speaker
For the speaker I chose to use the Boom Tunes speaker. The Boom Tunes speaker is described on Amazon as:
a compact, lightweight device that turns anything into a speaker that lets you play music around the house, outside, or anywhere you go! Simply plug it into any ipod, music player, or computer and stick the Boom Tunes on a box, table, water bottle or any surface that reflects sound! The bigger the object, the louder the sound. You can turn anything into a speaker- from boxes to cups, to cans, coolers and tables, and even sneakers....almost anything you can think of! The secret is the vibration pod that transfers crystal clear sound with treble and bass to any object. Stick it on almost anything and BOOM...it's a speaker."
It was a simple matter to attach a small mirror to the sticky part of the Boom Tunes speaker.
Mount the speaker with the mirror attached:
The compact size of the speaker makes it easy to aim it at the spinning mirror and easy to rotate it on its mount. To aim the laser beam at the spinning mirror, the mirror spinning motor should be off (switch off the Snap Circuits motor driver circuit) and its non-reflective side facing the speaker mirror. Once you've got the laser beam aimed from the speaker mirror at at the non-reflective side of the stationary spinning mirror, send a lower frequency sine wave from your sound source (in this case, my iPod) through the speaker. Usually you'll see the laser dot form an oval shape. That's when you have to rotate the speaker mirror until it forms a straight vertical line. Then you can switch off the sound and then make sure the spinning mirror will reflect the laser beam to your graph paper target screen.
Important Note: the Boom Tunes sticky pad must be cleaned before attaching the mirror! It's actually pretty easy--I just used soap and water and a q-tip. If you don't clean it, when you send lower frequencies thru the speaker it will shake the mirror off the pad. You can see the laser scan starting to degrade at the end of the video from my original LaserOscope because the mirror was starting to detach from the sticky pad:
Makeup Mirror and Lego Connector
To mount the makeup up mirror, I glued it to a Lego "Axle to Pin connector with Friction (43093)" part with ordinary school glue.
Build the Lego Mirror Spinner
Attach the Snap Circuits base plate to Lego base plate
Snap Circuits is an educational toy that teaches electronics with solderless snap-together electronic components. Each component has the schematic symbol and a label printed on its plastic case for easy identification. They snap together with what appear to be ordinary clothing snaps. The components also snap onto a 10 X 7 plastic base grid somewhat analogous to a solderless breadboard.
All the kits include manuals printed in color with instructions for ages 8 or older and with easy to follow diagrams to assemble the projects. The illustrations for each project look almost exactly like what the components will look on the base grid when finished. Because the electronic symbol is printed on each electronic component, once the project is completed, it will look like a printed electronic schematic.
Snap Circuits might seem at first to be somewhat pricey. A Snap Circuits resistor costs $1.49 USD. A resistor from Mouser costs fifteen cents. On the other hand, the Snap Circuits Motion set (the set I used for this project) costs $84.95 whereas the littleBits base kit costs $99.00. So, you get a lot more Snap Circuits than littleBits and at a lower price.
As an introduction to electronics, both Snap Circuits and littleBits have an advantage over breadboard and conventional spring connector electronics kits. Some folks might find working with electronics and breadboards a bit too fiddly. Spring connector kits are easier to use than breadboards, but once you build a circuit of any complexity with a spring connector kit, it ends up looking like a rat’s nest of wires that’s difficult to troubleshoot.
It’s much easier to snap together a circuit with Snap Circuits and to troubleshoot problems. If you switch a project on and nothing happens, you can, at a glance, compare the circuit in the manual to the circuit you’ve built and easily find where you’ve connected something incorrectly.
Build the circuit to spin the Lego mirror Spinner:
All the parts before setting up LaserOscope II
LaserOscope II set up and running:
If you've got the laser aimed properly and it's formed a vertical line on the target graph paper screen, switch the Snap Circuits motor driver circuit on. Adjust the 10K linear potentiometer (RV2) until the mirror starts to spin. You should see a a wave form similar to the one below tracing across the graph paper screen.