Available as an assembled Module and as a DIY project.
This Module is currently available.
Positive Slew Generator
The ES09 can be used as both a rising slew rate controller, or a upwards sloping ramp LFO by hooking the lower pulse out into the Start input. In this configuration it also operates as a utility oscillator, suitable for fixed key sequencing and general sound effects and noise making. It is not suitable for tracking a keyboard.
The slew rate is adjustable from ~500uS to ~17 seconds.
https://www.elby-designs.com/webtek/euro-serge/es09-positive-slew/es09.htm
1 Users are observing this
These merchants probably sell this module. Huh?
