Packaging the Arduino

The next challenge was physical. I needed to mount an Arduino Pro Mini board in my reclaimed Sea & Sea TTL converter housing. Should be easy. The housing was much larger than the Pro Mini board. The Pro Mini board was smaller than the Sea and Sea board I removed from the housing.

Nope. It quickly became obvious that Internal clearance was at a premium. The CR2 battery compartment intruded into a large portion of the internal space. The bulkhead connectors and potentiometer controls took up lots more space. These constraints left only 1 mounting position for my Arduino board: the exact same place as the original Sea and Sea board.

Except the Pro Mini board was smaller and did not cover the mounting posts of the original board. I needed to extend the Pro Mini board in order to mount it. This was accomplished by taking a standard perfboard and cutting it to size. The Pro Mini was then mounted to the perfboard via header pins. This ended up with a thick board. Too thick. The Pro Mini components rested against tabs projecting from the metal bracket around the potentiometers with a potential to cause shorts. This lack of clearance problem was solved by bending the tabs over. The tabs appeared to be a standard mounting feature of the potentiometers and were not being used in this case.

I now had a solution to mount the Arduino board. Next up was connecting the various controls and bulkheads. Which presented another challenge.

The original Sea and Sea board featured a set of connectors, 1 connector for each control / bulkhead. These were mounted on both sides of the board, closest to the connection. The use of connectors allowed the board or any of the controls / bulkheads to be easily replaced by unplugging and replugging. No soldering iron required, The Pro Mini used 2 standard 0.1" spaced headers. These are much larger than the Sea and Sea board. The Arduino I/O pins where logically arranged along the 2 headers.

At first glance all I had to do was create a bunch of new connectors for the existing wire loom. But I had the following challenges:

  • the 0.1" connectors were too long
  • the Arduino headers where in the wrong place
  • the connector specific pins where not adjacent
  • The standard 0.1" female connectors projected too far above the plane of the Arduino board. They collided with the internal surface of the housing. So standard off the shelf connectors were not suitable.

The Arduino headers are located down each side of the board. This is totally logical. But once the board was mounted in the housing, the various controls and bulkheads would physically interfere. Re-examination of the Sea and Sea board seemed to have the connectors placed randomly about the board. Closer inspection revealed that the connectors were strategically placed so that each connector was located so that it was between the controls and bulkheads and board mounting posts. This need greatly reduced the potential placement locations for connectors.

Connecting directly to the Arduino header was not feasible as the pins were in the wrong order. A potentiometer needed 3 wires: +, ground and an analog input from the tap. These pins where not located next to each other on the Arduino. They were spread around. 

This observation revealed the (now) obvious solution:

  • locate the connectors on the perfboard in spots that did not mechanically interfere with controls / bulkheads
  • solder wires from the Arduino headers to the connector headers

This resulted in a session with my soldering iron and several spools of different colored wire wrap wire. I then carefully removed the wire looms from their original connectors and individually jammed each wire onto the 0.1" header pin.

Not elegant, definitely not production quality, but it worked just fine.