Here it is!

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Postmortem

The final product turned out pretty great.  I’m glad I followed through and turned RevA into a fully functional product despite the constant desire to redesign every time I ran into issues.

• Silkscreen text too small.
• Instead of 22uf Ceremic caps switch to 47uf electrolytic for cost savings
• Shink size of SOIC pads so they get less solder
• Use 4mil stencil
• Add stencil alignment tooling holes to board and stencil 
• Reduce BOM.  Since I’m used to working on high performance RF devices I tend to use too many bypass caps for such a low speed design.
• Use smaller microcontroller.  The ATMeega2560 was too large physically, feature wise, and cost wise.
• Use smaller vias
• Figure out how to use interrupts with wiznet to cut down polling
• Reduce board size.
• Switch to using 2 boards: 1 for relays+ drivers, and the other for the main circuitry.
• This will allow changing the relay board for some NEC UB2-12NJ relays if I want to do a low-voltage version.
• This will allow the main RJ45 jack to butt up to the back panel.
• Add the Wiznet reset line to avr so I can reset manually if watchhdog timer fails.
• Test points!
• Bottom size copper keepout around relays to avoid arcing
• Add an LED per relay.
• Add power monitoring per outlet
• Finish zero crossing detector to improve relay lifetime.
• Switch the Power button LED to a port with PWM output so I can do the “breathing” LED effect.
• Make the power-monitoring module an addon (CT, Zero crossing, Vsense)
• Mirror RJ45 differential termination so they stay coupled better.
• Enclosure cutout for the IDC power inlet was the wrong size.  Had to file it down a bit.
• Need a rear on/off switch with integrated 15A breaker for power cycling the logic.

Debug Environment

This is what real work looks like

In order to debug I used the following:

• ICSP Programmer. I use the UsbTinyISP programmer from Adafruit.
• Network Serial Port.  I use a BrainBox ES246 network serial adapter so I can access the serial console while on Wifi since I like to debug while lying in bed.
• Current Limiting Bench Power supply
• Fluke 87v DMM
• Rigol Oscilloscope
  

Arduino Environment

Before I could even get started debugging, I needed to create a custom boards.txt and pins_arduino.h files so the Arduino programming environment would know how to map things like the friendly “LED_BUILTIN” to the actual I/O register.

 To keep thing simple, I started with the timeless “Led Blink” sketch. 

Wiznet W5100 Debug

Programmer, Serial Port, and Ethernet Hooked Up

I discovered a short on the 1.8V LDO output of the W5100.  After some rework with the hot air and some solder wick I managed to repair the short.  It looks like I made the pads extend under the device a little too far making it very difficult to clear a solder bridge under the IC.

After that, it was smooth sailing…well not exactly. The 3.3v and 1.8Vdd and 18.Vda rails all were outputting the correct voltage, and much to my surprise the Link and Activity lights on the RJ45 mag jack were lit, so at least the chip was alive.

Oscilloscope and Hot Air Rework Station

I probed around the SPI bus a bit, I discovered the SlaveSlect signal was not toggling.  It turned out that the SlaveSlect pin was hard coded in the Arduino Ethernet library.  Having it configured with a header or constructor would have been much better.  Nevertheless, another quick hack and the Arduino Ethernet tutorial I was using was fully operational.  Hello World!

Layout

Today I finished the layout for the Network PDU-S.  I used Kicad for the entire PCB process.

The board is much bigger than I would have liked.  Next time I will probably put the relays on a separate board from the logic.

Network PDU-S RevA layout

Circuit Design

The Network PDU-S will be based on the Arduino Ethernet board, however instead of the ATMega328 I’m going to use an ATMega2560.  This is the same chip that is used in the Arduino Mega, and I’ve used it in several designs before so I’ve already got most of what I need to create the schematic.

For the Ethernet controller, I’ve chosen to use the same Wiznet W5100 chip as the Arduino Ethernet so I can take advantage of the existing code libraries.

I’m including a Max232 RS232 to TTL level converter in the design.  This will be used for debugging, and possibly included in the final product to send/receive commands to RS232 compatible devices.

Schematic

Here’s the top level schematic designed in Kicad:

Design Requirements

1. Its simplest function is power distribution.  the Network PDU-S  will provide a 6rear + 2front outlet power strip.

2. This device includes a programmable sequencer that allows you to power equipment on/off in a specific order.

3. This device includes network control.  From a webpage you will be able to configure the sequencer settings as well as toggle individual outlets on and off.  The device will also be able to send commands to other sequencers allowing you to control the power-up sequence of equipment at remote locations via the internet.

Motivation for this project

1. I travel a lot for work, and sometimes I need to remotely power cycle the servers in my home data center.

2. For my A/V work I need a power sequencer to turn on the sound board and amplifiers in a specific order to avoid equipment damage.

3. In some A/V venues I need to sequence equipment in the sound booth, on stage, and also back in electrical rooms.

4. I would like to get per-outlet power metering so I can closely monitor peak/average power consumption of all of my equipment.

 High Level Design Document

High Level Block Diagram

I created this diagram with DIA diagram tool..