eurorack voltages
Altered from the Henry Thomas design
https://electro-music.com/forum/viewtopic.php?highlight=attack+decay+555&t=61297
I've increased the voltage output for eurprack compatibility.
Second trigger switch works AR rather than AD
Added a switch and an inverting transistor to once triggered it will keep cycling.
Needs additional filtering on the power rail to protect the rest of the rack from the 555.
Extra transistor makes the envelope cycle, there's a switch to turn that off.
