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A YIPPEE! moment…the Healthy pH Dev-Rev3 Shield’s Gerber files were sent off to OshPark!  The kicad files are located in this GitHub location.

The Goal

The goal of this post is to discuss the changes to the design and layout of the Healthy pH Dev-Rev2 Shield that went into the Healthy pH Dev-Rev3 effort.

Thanks to Those That Went Before

Chris Gammell continues to be a major reason I am able to make progress.  I learned a lot taking his Contextual Electronics courses – and highly recommend them if you are breadboard prototyping circuits and want to take a twirl at building PCBs with SMTs.  This time around, Chris was instrumental in guiding me through the layout choices.

OshPark is a terrific fabrication service.  I am very impressed with their product and their support.  Highly recommended!

Design Changes

After running the test harness (code at this GitHub location) I had written and playing around with the Shield, I had a list of design changes to make: 

RGB LED
Remove TP19,TP10
Remove TP8
add Text and Logo
fix pin layout of voltage regulator (7805)
fix barrel jack drill holes
enlarge TB pins
remove TP17
remove TP2, TP3, TP4, TP5, TP6, TP7
connect 2nd Ard GND pin
remove TP14
move TP12 text
put ‘1’ close to 1st conn of 8 pos TB
remove TP14
remove TP12, TP 15, TP13, TP16
remove TP11
remove TP18
change R15 to 1K
.1 R15 1K
.1 Thermistor
add .1 uF near voltage divider (r3, r4)

I discussed these changes in earlier posts.  It was terrifically exciting to see the software interact with the hardware as well as view the analog signals on a scope!  This gave me a much better idea on what is going on within the circuit(s).  It also gave me insight into how far I am from using the shield in a hydroponic system.  I hope after the next rev I can use the shield…but typically I am overly optimistic…

Layout Changes

Changes to the layout caused many a stumble on my part.  I had a major D’OH NO-NO on my first attempt at the layout for the Healthy pH Dev-Rev3 Shield:

HealthypHDev-Rev3FirstAttemptDOH

I had the power line for the analog circuit going through the middle of the MCP3901.  

I got caught up in not crossing any tracks.  Layout is harder than it looks. For me, layout is like chewing gum, patting my stomach, and spinning a plate on my nose at the same time.  I bet a great video game could be made out of the puzzle and the resource constraints…but I diverge…

Here’s what I ended up with:

Healthy Dev-Rev3 Layout

Both the analog power source (V+_Wallwart) and the digital power source (V+ARD) are wide rivers running through the board and out of the way of the chips in the same way it seems rivers typically don’t run through the middle of a building.  I also placed the decoupling capacitors closer to the chip whose power line it is supposed to be cleaning up.  Other than that – tracks were thickened.  The pump circuit had minor touch ups and most of the test points were removed.

 

It is like anticipating a special gift to wait for the purple mailer from OshPark with the 3 PCBs in it.  I’ll keep busy…next on my list is…SHOPPING!…which I find shopping for parts on digikey.com to be much more fun than shopping for shoes.  But perhaps not as exciting as the impulse buys I can’t seem to stay away from on ebay.com and amazon.com.

 

 

Thanks for reading this far.  Please find many things to smile about….

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