When Bajdi wrote his blog, https://www.robotshop.com/letsmakerobots/node/40026 , about his undershield for the Arduino Pro Mini clones I was very interested and excited. This was because over the last few months I have purchased a few (20) of these Pro Mini clones myself. I was elated to see that there might be an easy interface board for my future projects.
Then, I realized that the Pro Mini version that I had procured was different than that which Bajdi had based his design upon. The version that I have has four additional pins (A4,A5,A6 and A7) which are accessible via through holes positioned behind the main row. So I set out to make a similar board that also broke out these pins as well. Below is what I came up with:
I posted about this in Bajdi's blog and then realized that I should have created a new blog. It was not right of me to clutter his blog with my babble. So I started this blog.
The board is similar to the Bajdi design. I originally had designed it with a SMD 78L05 that I had on hand, but was not happy with the low current rating of 200mA. After reading his blog I went onto Ebay and ordered some AMS1117s and reworked the power supply. I used all SMD parts and included a LED on the regulated power output of the AMS1117. LEDs are cheap and I like seeing that power is available. The RAW voltage will be indicated on the Pro Mini, so I wanted an indicator for the regulator on the breakout board.
One departure from Bajdi's design was that I routed the board to arrange the pins somewhat like you might find on an Uno board. That is to say that they are arranged anti-clockwise in numerical order. And I omitted routing VCC/GND/RAW from the Pro MINI to the pin headers.The board turned out a little larger than his design. This was because I required a little more room for routing signals.
Overall I am pleased with the design and I have ordered a few boards to test upon my return home. I have already spotted a few minor things that I will change in the next iteration. These are mostly related to pin labeling and additional information placed on the silkscreen layer. I may also position the input power terminals on the underside at the board edge of future iteration and shorten the board a bit. And I may add a second schottky diode to provide reverse voltage protection for the regulator input. I have to consult the data sheet, but I don't remember if it says that the regulator has built in reverse voltage protection.
Thank you for sharing your design and I hope that it was alright that I drew inspiration from your work.
Thank you for helping me get started designing boards. Without your help I would never have been able to accomplish anything like this. You were right when you said that it is addictive!
I welcome any comments or suggestions on things that I may have screwed up or ways that I might improve upon the design.
Sorry that it has taken so long, but here are the eagle files.