A decoder-based irrigation controller comprising a controller housing; a first microcontroller within the controller housing; a decoder interface coupled to the first microcontroller; a first connector coupled to the first microcontroller; a removable cartridge configured to removably and detachably coupled to the first connector to fit into the controller housing, wherein the removable cartridge comprises a second microcontroller; and a handheld barcode reader, wherein the handheld barcode reader comprises an optical reader configured to read an optically readable pattern from each of the plurality of decoder units, wherein the handheld barcode reader is configured to transfer data read from the optically readable pattern of the plurality of decoder units to the second microcontroller of the removable cartridge, and wherein the data read comprises an address of each of the plurality of decoder units.