diff --git a/light9/collector/output.py b/light9/collector/output.py
--- a/light9/collector/output.py
+++ b/light9/collector/output.py
@@ -133,11 +133,11 @@ class Udmx(DmxOutput):
                               scales.PmfStat('update'),
                               scales.PmfStat('write'),
                               scales.IntStat('usbErrors'))
-    def __init__(self, uri, numChannels):
+    def __init__(self, uri, bus, numChannels):
         DmxOutput.__init__(self, uri, numChannels)
         
         from light9.io.udmx import Udmx
-        self.dev = Udmx()
+        self.dev = Udmx(bus)
         self.currentBuffer = ''
         self.lastSentBuffer = None
         self.lastLog = 0
diff --git a/light9/io/udmx.py b/light9/io/udmx.py
--- a/light9/io/udmx.py
+++ b/light9/io/udmx.py
@@ -24,8 +24,14 @@ or https://github.com/markusb/uDMX-linux
 cmd_SetChannelRange = 0x0002
 
 class Udmx(object):
-    def __init__(self):
-        self.dev = usb.core.find(idVendor=0x16c0, idProduct=0x05dc)
+    def __init__(self, bus):
+        self.dev = None
+        for dev in usb.core.find(idVendor=0x16c0, idProduct=0x05dc, find_all=True):
+            print "udmx device at %r" % dev.bus
+            if bus is None or bus == dev.bus:
+                self.dev = dev
+        if not self.dev:
+            raise IOError('no matching udmx device found for requested bus %r' % bus)
         log.info('found udmx at %r', self.dev)
         
     def SendDMX(self, buf):