https://github.com/UA3MQJ/fpga-synth/blob/master/wiki/MCP41XXX-MCP42XXX.pdf
http://www.ebay.com/itm/10-PCS-MCP41010-I-P-DIP-8-MCP41010-Digital-Potentiometer-NEW-/291205963691?pt=LH_DefaultDomain_0&hash=item43cd3a5fab
http://www.ebay.com/itm/10pcs-MCP42100-I-P-Manu-Microchip-Encapsulation-DIP-14-Digital-Potentiometer-/221465572689?pt=LH_DefaultDomain_0&hash=item3390607551
http://www.ebay.com/itm/10pcs-MCP42100-I-P-MCP42100-Dual-Digital-Potentiometer-100K-SPI-Interface-NEW-/261838716571?pt=LH_DefaultDomain_0&hash=item3cf6cdbe9b