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Klavins Lab Turbidostat Wiki | ConstructionManual / Main Board
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Main Board

(page under construction)

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.

Attach:T_MB_1.jpg Δ Δ Step 1. Gather all parts and 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)
Attach:T_MB_2A.jpg Δ Δ Attach:T_MB_2B.jpg Δ Δ

Attach:T_MB_2C.jpg Δ Δ

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.
Attach:T_MB_3.jpg Δ Δ 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).
Attach:T_MB_4AB.jpg Δ Δ 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.
Attach:T_MB_5A.jpg Δ Δ Attach:T_MB_5B.jpg Δ Δ

Attach:T_MB_5C.jpg Δ Δ

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.
Attach:T_MB_6A.jpg Δ Δ Attach:T_MB_6B.jpg Δ Δ

Attach:T_MB_6C.jpg Δ Δ

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.
Attach:T_MB_7A.jpg Δ Δ Attach:T_MB_7B.jpg Δ Δ

Attach:T_MB_7C.jpg Δ Δ

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.
Attach:T_MB_8AB.jpg Δ Δ Step 8. Solder on the RJ45 connectors.
  • clip on the RJ45 connectors and solder them.
Attach:T_MB_Trouble1AB.jpg Δ Δ

Attach:T_MB_Trouble1C.jpg Δ Δ

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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Page last modified on March 10, 2014, at 10:38 PM