More information is available (in Swedish) at http://www.npsalmodikonforbundet.se on the club's website (click on the button that says Kontaka oss [contact us] for a pulldown directory and on Öpna [open] to open an item in the directory. If you don't read Swedish, you can find some cool pictures by scrolling down to Bilder [pictures] and clicking on the Öpna button.
A mostly Norwegian-American group in Minnesota, called the Nordic Psalmodikonforbundet (no umlaut in Norwegian), has a wealth of information in English at http://www.psalmodikon.com.
Here's what I wrote, translated into Swedish and (since I can't find my original draft anymore) translated back into English:
On 2 August, I led a workshop on the psalmodikon for the Bishop Hill Heritage Association in the old Swedish colony of Bishop Hill in Illinois. There were 21 persons. When I in the beginning of my appearance asked if they knew of the instrument Psalmodikon it was only two or three people who raised their hands.
I have a copy of an instrument made in Bishop Hill in 1870 and I showed how to play on it and got them to sing " A Mighty Fortress is our God" by numerical scores [the siffernoter] so they would understand how the numbers relate to the notes in the scale. It was great fun and I think the audience appreciated it.