Progress update!

The current state of the organ:

Electronics

• The PCBs have been redesigned to use connectors that are easier to assemble and work with, as well as surface-mount components to reduce the footprint and add mounting solutions.
• The input boards have been fully tested, and the output board design has been tested for basic function.
• The wiring harnesses for the keyboard are currently being assembled; completion is about 50% as of this post. It's a meticulous process that takes some attention to detail.
• The interface between the control boards and the main controller needs attention; live input latency may be an issue with the current design due to frequency limitations of the isolation board.

Software

• The software for MIDI playback is functional, but improvements are planned.
• Live input from the keyboard has been tested, but live output to the organ may have latency issues. I'll need to put together a test system, probably with just one set of horns, before I can evaluate latency.

Hardware

• Manifold configuration is basically set: I'm just gonna drill and tap some 2" PVC pipe for 1/2" NPT and screw in the valves directly. This will probably require removing the solenoids from the valves while assembling, which will be time-consuming, but it's got a very low part count; I only need to buy enough pipe and fittings to have room for all of the valves to be attached.
• I'm going with bigger, more expensive valves than I initially planned, because I just can't get the throughput I need with the small ones unless I want to design and build a bunch of pneumatically-controlled valves and use the small ones as controls, which adds a ton of work to the build. I've talked about this before, and I had a valve design that seemed more likely to work, but the complexity is too high.
• Horn designs are pretty much set, although I need to spec the sizes for wavelength vs. pipe diameter. Being fully chromatic, I'll have a difference in tone when the size changes, but hopefully it won't be too dramatic a change.
• Once the horn sizes are determined, I'll need to figure out how to package everything. I'd like to keep the thing as compact as possible, and that probably means folding the largest horns at least twice.
• If possible, I'd like to include a sort of damper box with louvers that can be opened or closed to somewhat reduce the sound output when necessary. This may prove difficult, impossible, or ineffective.

About air horns and their construction

Air horns were one of the first puzzle pieces that gave me the idea for this project, and while I don't remember what originally got me interested in them, I remember finally figuring out how they work and being surprised by how simple the design actually is.

I'm not dead yet!

The blog has sat idle for more than a year, and I'm sure that any visitors between then and now have been disappointed by the lack of content (and there's been quite a lot of content planned that's yet unwritten), but progress has been made in the interim. I've redesigned the PCBs completely (they now use surface-mount components, RJ12 connectors instead of pin headers for communication, and proper IDC connectors for the main I/O interfaces), I've decided on a more expensive but much (much much much) less labor-intensive solution for valves, and I now have an oscilloscope that will be quite helpful for troubleshooting if necessary (like, for example, the I/O isolation board with the seemingly glacial-speed optoisolators). I'd like to write posts about the SPI interface, about some of the component choices, about how the code works, and a lot of other things that deserve at least a few paragraphs worth of detailed explanation. I'd also like to get a diagnosis and start some sort of treatment for ADHD, but that requires me to stop procrastinating and actually make some progress.

I've learned a lot since I started this blog, and I'm sure I've plenty more to learn before the project is finished (and who knows how long that will be yet). I've learned a lot about python, about electronics, about pneumatics, and about my variety of personal challenges. I don't want to get too existential, but I'm looking forward to moving forward after all this time.