labsw/LOG: reworked power supply bypassing

labsw/LOG

@@ -150,6 +150,28 @@ Milled face plate #3:
     LEDs to the pull-ups. Work-around: add 10 kOhm in parallel to each
     LED.
 
+--- Wed 2011-09-07 ------------------------------------------------------------
+
+Rework:
+- problem: labsw occasionally (around 1% of all cycles in an automated
+  test loop) gets some configuration bits wrong. The pattern observed
+  so far is that, in an attempt to turn on CH1, then CH2, CH1 comes on
+  normally while CH2 either doesn't come on at all or the relay switches
+  but the LED doesn't.
+- analysis:
+  This may be a problem with the power supply or with USB. Consider
+  some or all of the following improvements:
+
+  - follow SiLab's recommendations for regulator bypassing more closely
+  - enable the VDD monitor to catch brown-outs
+  - add ground areas to shield CPU and USB
+  - add redundancy to EP0 protocol
+  - add bead to relay power, to prevent upsetting the 5 V rail
+- rework:
+  Implemented power supply bypassing according to SiLabs' recommendations:
+  - added 4.7 uF in parallel to C1
+  - added 100 nF in parallel to C2
+
 ---------------------
 
 (next PCB run)
@@ -174,16 +196,3 @@ Pending:
   3) drive opto LEDs from 3.3 V instead of 5 V (NOT ! Regulator
      can only provide 100 mA, which wouldn't be enough if more than
      two opto-couplers are active.)
-- labsw occasionally gets some configuration bits wrong. The pattern
-  observed so far it that, in an attempt to turn on CH1, then CH2, CH1
-  comes on normally while CH2 either doesn't come on at all or the
-  relay switches but the LED doesn't.
-
-  This may be a problem with the power supply or with USB. Consider
-  some or all of the following improvements:
-
-  - follow SiLab's recommendations for regulator bypassing more closely
-  - enable the VDD monitor to catch brown-outs
-  - add ground areas to shield CPU and USB
-  - add redundancy to EP0 protocol
-  - add bead to relay power, to prevent upsetting the 5 V rail