This week we also worked through some safety concerns with the physical interface. Each solenoid is rated for 400mA and 12V, with 69 solenoids we’d need 69*0.4A = 27.6A of current to power all of them. Running ~30A along one bus is extremely dangerous if exposed to human contact. Anything over 10A will likely result in death.
I did some digging into what others in the player piano community had done for their physical interface’s, and what I discovered was a bit shocking. Many of the the builds online I saw used 2 power supplies, at 15A each. This is still incredibly dangerous, but it got me wondering whether or not we could continue divvying up the supplies. I realized was could also make use of power strips, that can in total supply 15A across all its outlets before an internal breaker is set off. In order to make sure we’re being safe while building our physical interface, we’ve divided the 69 solenoid array into 9 segments of 8 solenoids (the last segment will only have 5). Each segment will have their own individual power source, and with 9 segments, each segment needs 27.6A / 9 = ~3.1A. 3A and 12V is a very common power supply specification, which means we can plug in an array of 9 3A/12V power supplies onto a power strip, and still power our entire system safely.