... | ... | @@ -18,10 +18,12 @@ The hardware design files were created and can be edited in [KiCAD](http://www.k |
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PDF versions of the electrical schematic and PCB layout can be found in the root directory: `dstat-mainboard-sch.pdf` and `dstat-mainboard-pcb.pdf`.
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# Materials
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## Printed Circuit Board (PCB)
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![full PCB](/images/Full_PCB.jpg)
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One DStat mainboard PCB is required for each potentiostat.
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The specifications of the PCB are tuned for the [Pentalogix](http://www.pentalogix.com) US Quickturn Prototype PCB service, but many other companies are capable of fabricating the board.
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Fabrication files can be generated with KiCAD or can be found in the `gbr` directory as standard Gerber files.
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All files use mm as base units, apart from the drill files which are generated with customary units.
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All files use mm as base units.
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## Components
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The list of electronic components required to build the DStat can be found in the `dstat-mainboard.csv` file.
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A combined parts list with suggested components can be found in the `dstat-mainboard-partslist.csv` file.
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... | ... | @@ -36,10 +38,10 @@ The naming of the references in the file and notes regarding component selection |
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| CON | PDI connector | 2x3 2.54x2.54mm pin header for programming µC |
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| COUNTER | Counter electrode connection | Single hole for soldering wire or connector |
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| FB | Ferrite bead | At least 40 Ω @ 100 MHz. DC resistance < 100 mΩ |
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| IC | Microcontroller | |
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| IC | Microcontroller | Make sure this is not the QFN package |
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| L | Inductor | |
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| P | Various connectors | 2.54x2.54 mm pin headers |
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| R | Resistor | 100 values can be wide tolerance parts (5%) all others should be 2% or better |
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| R | Resistor | unless otherwise specified, 100 values can be wide tolerance parts (5%) all others should be 2% or better |
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| REFERENCE | Reference electrode connection | Single hole for soldering wire or connector |
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| RSHIELD | Reference electrode shield connection | Single hole for soldering wire or connector |
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| U | Integrated circuit | |
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... | ... | @@ -50,6 +52,8 @@ The naming of the references in the file and notes regarding component selection |
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| X | Quartz crystal resonator | Surface mount HC49 package |
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## Tools
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![solder paste](/images/paste.jpg)
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To assemble the PCB, a few tools are recommended:
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* soldering iron
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* inspection microscope or magnifier
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... | ... | @@ -64,28 +68,46 @@ To assemble the PCB, a few tools are recommended: |
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A simple way to speed up assembly of the PCB is to use a small scale reflow technique in which solder paste is applied to the PCB, then heated with a hotplate to connect the components.
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The mainboard can be soldered by hand but the fine pitch components make this difficult.
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![bare pcb](/images/PCB-bare.jpg)
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1. Apply a small quantity of solder paste to each pad on the front of the PCB.
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Pads for fine-pitch components can be covered with a continuous line of paste for each side—the surface tension of the melted solder will remove most solder bridges once heated.
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![PCB with paste](/images/PCB_paste1.jpg)
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![PCB with paste](/images/PCB_paste2.jpg)
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1. Using tweezers, carefully populate the front of the PCB with surface mount components, making sure of the correct orientation of ICs. (Match the corner of the IC marked with a dot with the corresponding mark on the PCB)
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The solder paste will help keep the components in place.
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Perfect alignment isn't necessary as the surface tension of the solder will center the components once melted.
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![PCB with components](/images/PCB_parts.jpg)
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1. Heat the PCB on a hotplate following the recommended temperature profile for your soldermask.
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Remove once cooled.
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![PCB on hotplate](/images/PCB_hotplate.jpg)
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1. Inspect the front of the PCB for solder paste which has not completely melted, components that are not soldered to their pads, and pins on components that are bridged together with excess solder. (optical magnification is useful)
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Defects can be corrected with a soldering iron by applying heat to single pins or removing excess solder with solder wick.
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![IC with bridged pins](/images/PCB_bridged_pins.jpg)
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1. Solder the remaining components to the PCB by hand.
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These include surface mount components on the back of the PCB and components that sit in holes (pin headers).
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![Pin headers](/images/PCB_through_hole.jpg)
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![Back components](/images/PCB_back.jpg_)
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1. Clean flux off the PCB using a suitable solvent, rubbing the surface of the board with a swab.
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Especially if using water, ensure the board is completely dry before proceeding.
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![PCB cleaning](/images/PCB_cleaning.jpg)
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1. Before attempting connection of the instrument, check for shorts from the power rails to ground using the multimeter. (The P8 connector provides both power rails and ground)
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If any shorts are found, inspect components for solder bridges.
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![Finished Board](/images/PCB_finished.jpg)
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# Connections
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| Connector | Function |
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| --------- | -------- |
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... | ... | |