Open source hardware
The goal of this project was to design and manufacture a few small circuits, and through them learn more about the process of developing open source hardware. These are the three designs I have taken from concept all the way through to having multiple board revisions manufactured and assembled:
MiniPM-LiPoly
This is a USB charger and buck-boost regulator for Lithium-Polymer batteries. Of the three designs, this one gave me the most trouble. The TPS6300x buck/bost IC I used is has the smallest footprint of any part I've worked with in the past, and has proven very hard to solder by hand. The process I've been using is to apply
solder paste from a syringe, then using my
hot-air rework station to reflow the solder paste. Using this method, it's very easy to apply too much solder past, causing short circuits under the IC.
I recently received the fourth revision of this board, but have not yet assembled it. Here's the revisions in order from left to right:
And the changelog:
rev 3:
-Switched from version to revision
-Switched back to mini USB for easier soldering
-Increased board size and component spacing
v2.1:
-Applied CERN OHL
-Added Open Hardware logo.
-Switched from mini to micro USB.
-Added mounting holes.
-Removed USB LED to allow room for mounting holes.
-Switched some discretes from 0805 to 0603.
-Better thermal management on TPS6300x
-Reduced board length (width the same for breadboard compatibility).
-Modified silkscreen to reflect compatibilty with both the TPS63001.
and the TPS63002 for 3.3v or 5v output.
v2.0:
-Added second row of headers to sit better on a breadboard and to
breakout more pins.
-Moved charging LED to next to USB connector.
-Added standard LiPoly JST connector.
-Licensed under CC BY-SA
v1.0:
-Licensed under CC BY-SA
PogoISP
PogoISP is a pogo pin adapter for 6-pin AVR ISP programmers, which eliminates the need to solder male headers on target boards. This board is designed to be a kit, which I plan to eventually sell unassembled. Pictured below is the first revision of the board, then the first and second together (second revision not fully assembled).
Here is the changelog for PogoISP; the revision 3 boards are currently being manufactured:
rev 3:
-Changed resistor layout to standard 10mm pitch.
-Grew drill size on pogo pin headers.
-Renamed headers on schematic to FROM_ISP and
TO_TARGET for clarity.
-Added OSHW logo.
-Add PogoISP page URL.
-Rearranged silkscreen a bit.
-Switched to CERN OHL v1.1 license.
rev 2:
-Reversed pinout so PogoISP is pressed down onto
target board.
-Changed discretes to through-hole.
-Removed decoupling cap; through-hole cap took up
too much space, and didn't seem too necessary.
-Added switch to toggle power from programmer to
target board.
-Shrunk screws/standoffs from 4-40 to 2-56 to make
soldering the pins through them easier.
-CC-BY-SA license.
rev 1:
First version
-Works as a programming 'bed', where target board
is pressed down onto PogoISP.
-CC-BY-SA license.
NHD-C12832A1Z Breakout
This is a breakout board for Newhaven Display's
NHD-C12832A1Z series LCDs. It includes a
TPS79530 fixed 3V 500mA low-dropout linear regulator to generate the supply voltage for the LCD. The TPS79530 has a rated maximum dropout voltage of 170mV and a maximum input voltage of 5.5V, so the board can be powered by either a 3.3V or 5V supply (or really anything in the range of 3.17V-5.5V). The supply should be able to source up to at least 450mA, as this is the rated maximum current draw for the LCD.
Also included on the board is a
CD4050 buffer, which is used to shift the SPI signals from the input level of 3.3V or 5V to the LCD's 3V level.
The board includes all external components required by the display, including a 10KΩ pull-up resistor on the reset line, and a 330Ω current limiting resistor in series with the backlight LEDs.
This board has come further along in the development process than the others, as the first revision worked great. The only change I had to make for the second revision was to fix the component numbering on the silkscreen. I order twelve revision 2 boards so I could have a small stock to put up for sale on
Tindie. The boards have arrived, though I've not yet put any together:
The process I had been using of applying solder paste by hand is way too slow for putting together more than a couple boards, so I had a solder paste stencil made by
Pololu, which came out great. I also ordered an assortment of 'Small Modular Snap Boxes' from Adafruit (like
this one), and have sorted my stock of components for the NHD-C12832A1Z Breakout into them, which should make assembly a lot quicker:
I've also created a 'product page' for the NHD-C12832A1Z Breakout
here, and I have the design files on Github
here.
All boards above were manufactured through
OSHPark.
![[paper clip]](/courses/source/wiki_images/paper_clip_tilt.png)
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