https://www.amazon.com/gp/product/B00FBM3JEG/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&psc=1

I recently bought this for my Pump It Up (5-key) soft pad and it works perfectly. It only requires minimal setup (need to download a driver, URL is provided in package), and then map the keys in StepMania and you're done! Hope this helps.

I’ve heard there were issues with that blue adaptor. I have used this other adaptor (Ostent brand) for a year without any problems: https://www.amazon.com/dp/B00FBM3JEG/

However, I use it with Autobleem not Project Eris. I’m not sure if the different emulators would cause an issue, though.