added 12V fuse. added ground planes to PCB and did nortons analysis o…

…n critical ground currents. neilh10/SensorModbusMaster#1
EnviroDIY · Feb 5, 2021 · 1775468 · 1775468
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diff --git a/knh002-MayflyWingShield/README.md b/knh002-MayflyWingShield/README.md
@@ -8,13 +8,18 @@ https://oshpark.com/shared_projects/ffQNVmrp
 
 This Mayfly wingboard interface supports   
 - RS485 on up to three physical connectors.   
-- new feature - local 120ohm termination 2mm jack. The installer can simply activate the RS485 120ohm termination resistor if needed.   
- RS485 physical line interface designed for long lines if required, one remote 120ohms, and a local 120ohms termination resistor.  
+- new feature - local 120ohm termination 2mm jack. The installer can activate the RS485 120ohm termination resistor if needed.   
+ This RS485 physical line interface designed for long lines if required, one remote 120ohms, and a local 120ohms termination resistor.  
+- new feature - 12V output has 100mA resetable fuse. Trips at 250mA, but will hold 100mA. If output wire is s/c will protect battery/processor reliability. 
 - new feature - TTL lines have power safe data lines.   
-  Powering routing that allows connection directly to the LiIon battery.  This faciliates a more efficient +12V generation and greater power resilency.   
+- new feature Powering routing that allows connection directly to the LiIon battery.  This faciliates a more efficient +12V generation and greater power resilency.   
 - new feature - power can be taken directly from the LiIon battery (a build option)    
+- a dual led shows RED flashes for transmit to RS485 instrument, Green flashes from RS485 instrumnent (response)
 - new advanced feature - fuel gauge LTC2942 ( build option )    
 
+Changes from the old Mayfly RS485 wingboard
+a) doesn't use the unmanaged hybrid.  These hybrids where of unspecified quality, and often didn't work. 
+
 Background (from original Mayfly Wingboard)    
 
 The [Modbus RTU](https://en.wikipedia.org/wiki/Modbus) *logical* communication protocol is typically transmitted using the *physical* [RS-485](https://en.wikipedia.org/wiki/RS-485) serial communication signaling standard.

diff --git a/knh002-MayflyWingShield/rev4draft/KNH002rev4bomAA.xlsx b/knh002-MayflyWingShield/rev4draft/KNH002rev4bomAA.xlsx
diff --git a/knh002-MayflyWingShield/rev4draft/knh002r4_rs485schematic.pdf b/knh002-MayflyWingShield/rev4draft/knh002r4_rs485schematic.pdf