The goal of this project is to take a guitar input and output a frequency that is half that of the input; dropping the signal down an octave. I was hoping to use a fairly simple technique using an ATTiny1614. After looking at the signal, I think this might be very hard if not impossible given the planned circuit. But I want to give it a go anyway. There is an anti-aliasing filter on the input. It might be the reason the higher notes have such a low output and the filter might be shifting the phase of the overtones.

Just a quick video to bring closure to this prototype. It did not spin well in the past because the pivoting part would wedge on to the wooden arm and stop it from spinning. I added some bits of tape to prevent that and it appears to spin quite well. It started despite being only two wings. The pivot would swing a lot as the turbine came up to speed or was under a load and then settle down to minor movements.

A small-ish subwoofer using an isobaric configuration. This uses two 8" woofers in a clam shell arrangement. Theoretical frequency response extends down to 29 Hz.

Putting some "full range drivers" in a ported box. In this box, I can hear frequencies around 70 Hz, but the volume seems to level out around 120 Hz. This was about 40 Hz lower than with the sealed box.

Adding tweeters and a sub-woofer to the flat speaker for better frequency response.

A look at a simple stereo speaker and amplifier using a baffle or dipole speaker. The amplifier is a PAM8403 based board that I got off eBay. I chose it because it had a volume control with an integral power switch. The speakers are 4 ohm Visaton FR-58s that I happened to have laying around.

A speaker made from Dayton Audio exciters. The sound quality is not as good as regular speakers, but its not bad. I could see using these for a radio or background music.

Documentation of the building of a "Loudred" speaker. The system runs off a 5 Volt, 2 amp wall wart. The 2.1 stereo amplifier is crossed over at 600 Hz, and driven by PAM8302A mono BTL amplifier boards from Adafruit. The smaller speakers for the ears are Tectonic TEBM35C10-4 2 inch, 4 Ohm full range drivers, and the center speaker is a Dayton Audio TCP115-4 4 inch, 4 Ohm woofer. The sound quality is pretty good.

A speaker designed for my office that is intended to be hung under a bookshelf. It is a 2.1 stereo that operates from a 5 volt power supply and uses 4 ohm speakers. The crossover frequency is set at 600 Hz using Sallen-Key filters implemented with 4580D audio opamps. I used three PAM8302 based mono amplifiers from Adafruit to drive the speakers. The two full range drivers are Visaton FR-58s which I chose for its flat response curve and low sensitivity of 81 dB. I wanted the sensitivity lower than the woofer ( a Dayton Audio 4" woofer with a sensitivity of 87 dB ) since I cut the gain on the center channel to avoid clipping. I was quite happy with the sound. The video sound test doesn't quite do it justice.

A brief demonstration of the X-acto Crayon Pro crayon sharpener that came in the mail today. It cost around $43 and is used to sharpen worn down crayons so their tip is like new. This product uses 120 VAC so it is powerful and does not require batteries. If there is a jam, the cutter can be cleaned. I'm not making any recommendations, just showing what it is in case someone wanted to buy one.

The wind was variable, but we had a gust here and there. The VAWT was able to turn but did not perform as hoped. I think the pivot point was to far from the center of pressure, it wasn't balanced carefully, and one pivot seemed to hang up. So I suppose I'll have to make another only put a little more care into the construction.

An introduction to Spatial Kinematics, or the math used to calculate where a robot's end effector is in 3D space.
This is the first of a short series talking about some terminology and an outline of how the math works.

Details from the construction of a small Sharp style vertical axis wind turbine. There is a little video of it trying to spin, but the wind was so light and variable it really didn't get going. I was happy it turned at all considering the size of the wings compared to the diameter.

A solar powered candle. This is basically a solar garden light using the QX5252F chip with a few modifications. The battery (1200 mAh NiMH) and solar panel (50 x 50mm, 2V) are a bit larger. The inductor (33 uH) allows more current to the warm white LED for a brighter light. There is a switch between the chip ground pin and ground. This allows the battery to charge even with the switch off. Like a solar garden light, the light will not go on if the solar panel is illuminated.

A short video showing how to calculate gear ratios for a planetary gear system that includes a compound gear.
Files for making the parts shown in the video can be found at:

Going over a spreadsheet for calculations in a Sharp style passive pitch control vertical axis wind turbine.

An overview of the theory behind a computational model of passive pitch control on a vertical axis wind turbine. This is primarily for future reference.

Some video of the 0.10 m^2 horizontal axis wind turbine in a modest breeze. The LED would appear to light up continuously; however, it flickers in the video.

Details of the construction of a 0.10 m^2 horizontal wind turbine using 3-D printed airfoils and mostly PVC pipe and fittings. A rotor with magnets was constructed using a Blue Diamond Almonds nut can, and the stator was made using a 3-D printed bobbin and wound with 26 turns of 26 AWG magnet wire.

This is a small solar powered LED light. The circuit uses a QX5252F chip and a 33uH inductor. It is basically the same as a solar garden light but with a larger solar panel, battery and LED. Also, the light is on demand as opposed to always on when it gets dark. On a full charge, the light might stay on for close to 6 hours.

I tried making a vertical axis wind turbine with a lower solidity because I wanted to see one operate with a fairly high tip speed ratio. I knew going in that it would not start on its own, and it certainly did that. I could not get it to start at all. Possibly because we did not have very good wind for weeks. Perhaps I did not get it spinning fast enough to keep the wings from stalling. In any event, it looks like this experiment was a flop. But I posted the video for documentation sake.

Details of the bearing and stator assembly for a 0.10 square meter VAWT.

A brief characterization of the VAWT generator and estimation of tip speed ratio (TSR) with some clips of it spinning in the wind. I don't have power production data. Our wind resource is quite poor, and we might not have enough wind to collect power data for some time. The TSR is in the neighborhood of 1.2 to 1.4; a bit low for a VAWT, but not unexpected for a small turbine with relatively large wing chord.

Details about the construction of the rotor for a 0.10 sq. meter VAWT.

A small 3D printed generator for a VAWT. This spins freely as opposed to the DC motor I used in a previous video. I did not put a lot of turns on the stator so the output voltage was quite small. I incorrectly estimated the power output at 1200 RPM in the video, it should be half that value (dividing Vrms squared by twice the stator resistance to account for a load), or about 0.8 Watts. That could be improved with an increase in the amount of copper in the windings.


Created 2 years, 1 month ago.

221 videos

Category DIY & Gardening

Documentation of various DIY projects related to Engineering.