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What we're calling the "main circuit board" is principally responsible for taking in turbidity measurements taken many times a minute and using those to determine the dilution rate for each chamber on a minute by minute basis. Additionally it connects to your Mac/PC to output all data and accept commands.
It should be noted that this main board connects to a 12V/x amp power source which can be dangerous. As such this part should be encased in a non-conductive material and particular care should be taken when working with and attaching wires to the leads. Further safety instructions are included in the Final Assembly section.
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| Step 1. Gather all parts and tools:
Tools
- Main Circuit Board
- tweezers
- CHIPQUICK solder paste (or similar)
Surface Mount Parts
- ATMEGA164a (orientation matters)
- Ceramic oscilator (orientation matters)
- 74HCT151 (296-9254-5-ND) (orientation matters)
- 150ohm resistor network (766-163-R150P-ND)
- 4x 1.0uF ceramic capacitors
- 1kohm resistor 0805
- 5x 10kohm resistors 0805
- button
- LED (orientation matters)
Through-hole Parts
- RJ45 connector (orientation matters, but it only goes in one way)
- Molex connector (orientation matters, but it only goes in one way)
- screw terminal (orientation matters)
- breakaway 0.1" header strip
- Large electrolytic capacitors (10-1000uF) (orientation matters (or it may explode))
- BS107 (orientation matters)
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| Step 2. Apply CHIPQUICK to the Main circuit board.
- To apply CHIPQUICK use the blunt needle adaptor to add a minimal quantity of solder.
- Apply CHIPQUICK to all areas where surface mount parts will be placed.
- Use tweezers to lay the ATMEGA164A onto the OD board and place it such that it so that each pin lays directly over its respective pad.
- Note how the dot on the part matches the dot silk screened onto the circuit board.
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| Step 3. Apply all surface mount parts in the correct orientation.
- Next add the remainder of the surface mount parts with special attention to orientation of each of the parts. (zooming in on the image may help).
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| Step 4. Solder all surface mount parts at 230C.
- Once all of the parts are on there and in the correct orientation they may be soldered into place at 230C using a standard laboratory hot plate. This work should be performed in a fume hood as gases will emanate off the board as the solder heats up and flux burns off.
- As the board heats the CHIPQUICK solder will go from having a dull grey appearance to shiny and metallic and small wisps of smoke may be visible.
- Once the solder on all parts become shiny and metallic simply use tweezers to slide the curcuit board onto a pot holder or other heat-tolerating substance. Be careful not to disturb the parts on the board as they will require a few seconds to cool.
- Note that once the solder cools it may have a dull finish if lead free solder is used. This is okay. Leaded solder should maintain a shinier finish.
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| Step 5. Place and solder the BS107.
- Readjust the leads on each BS107 so that they fit int the main circuit board. The orientation is indicated by the PCB silkscreening.
- Solder each of the BS107 in place.
- Trim the leads off each BS107.
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| Step 6. Cut the headers to size and solder to holes closest to the ATMEGA164a.
- Cut or break the headers to the appropriate length.
- Using poster tack or tape to hold headers in place and solder it on the surface mount part side of the main board.
- Solder the headers into the set of 2x5 holes closest to the ATMEGA164a.
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| Step 7. Solder on Molex connector and place the rest of headers into all other through-hole locations.
- As before use poster tack or tape to hold through hole parts into place before soldering.
- The molex connector clips into place and can be soldered without poster tack or tape.
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| Step 8. Solder on the RJ45 connectors.
- clip on the RJ45 connectors and solder them.
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| Troubleshooting Soldering.
- One common problem, especially when soldering the surface mount parts is that multiple pins may be connected by excess solder.
- To remove excess solder place this region under a piece of copper braid (aka "solder wick") and apply heat until the excess solder has been removed by capillary forces.
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