The one that I made is very similar to the link that BellaBoo listed.
I used a 4" x 4" ceramic tile (from Home Depot, Lowe's, etc) which gives a firm and heavy base that won't fall off of your sewing machine cabinet or table. I made a "pocket" for the tile to fit in and left room in the pocket so that I could stuff the top of it firmly with polyester batting for the pins.