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Building a MIDI Thru Box Part 5: Circuit Board Assembly and Final Parts List

Pete Brown - 03 July 2011

The custom circuit board arrived from PCB-POOL while I was away at MADExpo. Of course, I couldn't wait to put it together. In this part of the series, I'll assemble the circuit board. For information on the previous steps, and more photos, please see these blog posts

Final parts list for the circuit (does not include rack case hardware or power switch)

Parts for the optional front panel and MCU integration. This will be the subject of a later post.

  • LCD Panel (TBD)
  • Netduino or FEZ Panda
  • Several momentary buttons and switch caps

Before we get into assembly and soldering, here's a quick recap of the related steps.

Manufacturing Steps Recap

Below is a recap of the steps required in the manufacture of this board. For brevity, I only show the top layer of the board in the WIP photos.


Read more about the initial design and prototype in my post here.



Read more about the design of the board in my post here.







Solder Resist application, Silk Screening, and UV curing

Note how the through holes are still copper-colored at this point. They haven't yet been coated.


Surface Finishing

You can see both photos in my post here. This is where the coating was applied to the through holes.


The final board, in my hands


Component Soldering

Now, to soldering. I'm not particularly experienced with soldering, so it's not super clean. I've also never soldered a board that had this type of dull (almost white) plating on the through holes. I believe that's an EU thing to do with RoHS compliance. Ones in the US typically have shiny plating. I'm curious to see how that goes. (After soldering, I can say that the coating did work well - the solder flowed wonderfully.)

Resistors Soldered


After soldering the resistors, I did a continuity test with my multimeter to ensure that all the solder joints were good. I continued this check after each step in the rest of the soldering.

MIDI Jacks Soldered



In the second photo, you can see the gap between the MIDI ports. I definitely could have tightened that up to lose a little width on the board and provide more stability on the jacks (they should overlap). In addition, if the jacks were all overlapping as they should be, I could have potentially just drilled out a large rectangle in the rear panel, rather than 10 holes, for the thru ports. I could still do that, but the gaps are ugly, so I won't.

First Jumpers in Place


I have a number of jumpers on the board. Some of them are for front panel connections like the power LED and the power switch. Some, like the ones shown in this photo, are to allow a microcontroller like the Netduino to get in the middle of the signal.

Soldering Complete


All the soldering is complete at this point. All I have to do is press fit the chips.


I had to have at least one mistake.

When I assembled the board I realized one significant, but correctable error: I put the large 47uF cap inline between the 9v power in and the 5v regulator when it should have been a smoothing cap between the +9v in and ground. I had to remove the cap and do a little creative jumping to fix it. I didn't want to cut any traces, so I decided to instead wrap the negative leg of the cap to the nearest ground point (which also happened to be on a capacitor), and send the power side back underneath the board to complete the circuit.



Yes, it's ugly, but it works. In fact, it all works perfectly. Except for that one hiccup, which I diagnosed by checking the voltages in the circuit with my multimeter, everything worked fine. I tested it, and the MIDI signals were coming through wonderfully.

Next Steps

The next steps are:

  • Complete the rack mount case (drill holes in back, drill or send out the front panel)
  • Complete the Netduino and LCD panel add-on

I'm not sure in which order I'll do those. If I end up sending the panel out to be professionally done, I may simply do that first and complete the Netduino piece while the panel is being made.

posted by Pete Brown on Sunday, July 3, 2011
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