Ok well here is my Universal ATR box known as ATR.poly. This design covers both master and slave units. First, let me say that the Sterilite model #1961 has 8.75" x 5" of usable space for my baseboard. So here are my design rules: (1) All components will be plugged into the baseboard;  (2) There will be only one copper for both master and slave units; (3) The ATR.poly boxes are standardized. (4) The main components are plugged in so that means there are Female Headers with solder-tails mounted to the baseboard. Some components such as the I2C expanders are not installed in the master. Nor is the priority encoder SN74LS174 in the slave.

Signal NameRJ45  Pin
Data1
Data2
Ground3
Power6
Data Monitor9
Data Monitor10
Power Status11
ground2
RS-485 Interconnect Wiring
Signal NameFrom PinTo Pin(s)
DataMon.1.1J2.9Con1.6
DataMon.1.2J2.10Con1.7
DataMon.2.1J1.9Con1.8
DataMon.2.2J1.10Con1.5
Status.1.1J1.11Con1.2
Status.1.2J1.12Con1.1
Status.2.1J2.11Con1.4
Status.2.2J2.12Con1.3
Data1J1.1J2.1, wire white-orange*
Data2J1.2J2.2, wire orange*
GroundJ1.3J2.3, wire white-green*
PowerJ1.6J2.5, wire green*

* the pairs white-orange/orange and white-green/green should be twisted pairs.

WAIT YOU SAY! The Arduino plugs into the baseboard? Duh? Ok well, I am buying my Megas without headers installed. And then installing stacking headers on them.

RS-485 Communication is handled by a Module which contains a MAX485ESA. Interconnecting the RS485 multi-drop is accomplished by a pair of RJ45 connectors with status LEDs (they must not have any magnetics). The module just plugs into a pair of 1x4 headers on the baseboard. I am using standard ethernet jumpers 12" long. (this preserves the twist for RS-485 (specified in the spec). The pair of RJ45 jacks are just wired to each other pin to pin (see RS-485 Interconnect Wiring Table).

The Status LED is light from a CPU GPIO after initialization.

The Data Monitor LED is connected to the Arduino's RX1 and TX1. It really doesn't matter as only one will be high at a time.  The Inputs to the RS-485 module are also these ports as well.

There is also a dip-switch (4 poles){only on slaves} that is used on the slaves to identify the slave to the master.

As I got feed up with eagleCAD I am now using KiCAD. KiCAD has an almost Zero learning curve. This is my first drawing with KiCAD, it's hierarchical and I am showing the baseboard itself, and the dual RJ45 Module.

 

Stay Tuned More to Come

~ Cris H.

 

Addendum: Final Thoughts, One quirk that KiCAD has is its export function. It only exports as a PDF life (with a transparent background (you know the black and gray checkerboard) which is in its self a problem well you can see the damn thing. So first I tried image magic, that gets me to a png file but still with the background. So I grabbed my swiss knife gimp and opened it in layers. So now all you do is export it and turn off the background in the dialog. - fins.

 

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