In need of a waveform generator for another project, [David Cook] crammed out the old turntable to modify it for a handy hack: By adding a simple reflectance sensor to the pickup he turned it into a waveform generator that optically plays back arbitrary waveforms from printed paper discs.
[Dave] wanted to show off a project at his 4th-grade son’s school during their family science night. We haven’t heard of an event like this before but it sounds like a fabulous idea! He had a new laser he wanted to include in the project, and noticed that his son was learning about how ASCII maps letters to binary number when the idea struck. He ended up building an optical data transfer system that demonstrates binary code.
This presents a fantastic learning opportunity as the project invited the school kids to select encoded strips like the ones seen above to form a secret message. The laser is pointed at a photosensor which is being read by a Raspberry Pi board. The Python code looks for a baseline and then records increases and decreases in intensity. Since the translucent tokens have either holes or black lines for 0 and 1 the baseline approach does away with the need to clock in the data. [Dave] reports that everyone who tried out the experiment was fully engaged at the prospect of pushing pieces of tape through the sensor and watching their secret message appear on a monitor.
He was motivated to write about this project after reading about data transfer using an LCD screen and photosensor.
What can you make with a toilet paper roll, duct tape, and a graphing calculator? A stand for your homemade spectrometer. This is neither as pretty nor as accurate as a precision scientific instrument, but that doesn’t mean it’s useless. In fact, it works perfectly well for rudimentary observations. Light is shined through a sample solution, passes through a diffraction grating, then shows up as bands of color on the projection surface seen above. The photosensor mounted on the cardboard tube was pulled from a night-light, and is read using the ruler and the multimeter. This results in two data units that are used to graph the results. As long as you’re running test samples as a control this simple setup will yield useful information for the scientist on a shoe-string budget.