Avast Thar Matey,
Welcome prospective tribe member. The SPD-20 is not the only module that will do what you want. However, you should be aware that there are several different ways you can go. You can do a hardware module or you can do a software module (such as BFD2). I myself have a Roland TD-20 hardware module that will do what you want it to do, if you have the right pedal. I believe the TD-12 and TD-10 can also articulate a full range hi-hat. Since I am only familiar with the Roland TD-20, I cannot attest to this capability with other brands of hardware. Our tribal wizard (John Emrich) has a video that demontrates a fully articulated hi-hat using the software BFD 2 and a hatkat pedal. The video is located elsewhere on this site. It is also available on youtube, if you type in the search terms "zendrum" or "john emrich". I hope this helps.
Fair Winds and Following Seas,