diff --git a/ext/bscacquisition.py b/ext/bscacquisition.py
index 28efa25..da3ad3a 100644
--- a/ext/bscacquisition.py
+++ b/ext/bscacquisition.py
@@ -25,12 +25,13 @@ class BSCAcquisition(Acquisition):
             #print('Received %i' % i)
 
         # write out the data file
+        use_channels = channels or self.bscache.channels
         with h5py.File(filename,'a') as hid:
             # save the pulse ID
             singledata = [ele['pid'] for ele in data]
             pidname = 'pulse_id/group%d' % self.grp
             hid.create_dataset(pidname, data=singledata)
-            for chn in channels:
+            for chn in use_channels:
                 singledata = [ele[chn] for ele in data]
                 if not chn == 'pid':
                     dname = chn.replace(':','/')+'/data'