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!
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:
|add Text and Logo|
|fix pin layout of voltage regulator (7805)|
|fix barrel jack drill holes|
|enlarge TB pins|
|remove TP2, TP3, TP4, TP5, TP6, TP7|
|connect 2nd Ard GND pin|
|move TP12 text|
|put ‘1’ close to 1st conn of 8 pos TB|
|remove TP12, TP 15, TP13, TP16|
|change R15 to 1K|
|.1 R15 1K|
|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…
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:
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:
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….