Only after ordering three serial-to-TTL converter boards with level translators for both RX/TX and RTS/CTS (labeled “WaveShare” and featuring the Sipex SP3232), I figured those are made to connect a microcontroller as a peripheral. The seller must have had reasons to provide no photos of the DB9 port, from which it would have been too obvious that it only has a female connector.
The issue was easy to solve, though. Remove the female DB9 connector, replace it with its male counterpart (attention: the pinout is mirrored, so the connector must be mounted on the opposite side of the PCB), swap input and output connections of the level converter chip (don’t forget to cut the original traces on the PCB), and voila. Given the SP3232 only requires few external components and the board closely follows the reference layout, the job was finished within a matter of minutes.
Pins 2 and 3 (TX and RX) need to be swapped
Pins 7 and 8 (RTS and CTS) need to be swapped
Male DB9 connector soldered to the opposite side of the PCB and attached to a Teensy 2.0 with SD memory card extension board
So here’s another part of my endeavour to put left-over components from previous projects to good use, and again it’s got something to do with LEDs. This time, I set out to make an eight character 7×5 pixel LED display of type HCMS-2975 controllable from my computer. As I usually keep a batch of Teensy 2.0 available for such purposes, getting it done was a comparably quick job. No external components are needed when connecting these two devices, so it boiled down to connecting just five data pins and the supply voltage. I used Eagle to design a PCB (using the Teensy library from here and the display library – which I had to slightly modify to support the display with eight characters – from here).
As the resulting board was less than 1″x2″ in size, I decided to give Seeed Studio’s Fusion PCB service a try this time. Fusion PCB does not accept Eagle files, but provides an Eagle to Gerber converter job, which completed without any problems. After slightly more than 2 weeks of waiting, the PCBs had already arrived by airmail. Although one board would have been enough for me, Fusion PCB only sells batches of 5 PCBs at a time, and eventually even delivered seven boards (drop me a line if you want one). For a price tag of around $2 per board, the quality is remarkably good – only on one board the vias didn’t align very well.
When browsing the Adafruit shop last month, I came across the NeoPixel shield . This comparably inexpensive option to add 40 individually controllable RGB LEDs to an Arduino immediately caught my attention. With numerous applications in mind, I ordered an Arduino Leonardo and the NeoPixel shield to give it a try, especially because a ready-made Arduino library is available  (admittedly, I still prefer bare-metal C programs over the Arduino abstraction, but definitely enjoy the benefits of a ready-made clock-optimized driver implementation).
In order to call it a project, though, I wanted to put the stacked Arduino platform into a suitable enclosure. While numerous cases in even more colors exist for the Raspberry Pi, I was having a hard time to find a suitable enclosure for Arduino boards at all. I almost started wondering if no one was interested in putting their Arduino into a case when using it for anything other than prototyping. With the special requirement in mind that the enclosure needed to have a transparent cover, only very few solutions remained.
Eventually, I ended up ordering a Project Box for Arduino  from the Akafugu web store . Slightly skeptical at first, I was quite surprised by the great appearance of the case. Even with only little exposure to light, the edges have a nice glow. The assembly was straightforward and the Arduino without the shield fitted nicely. After adding the shield, however, the stack was too high to close the top cover.
As I was not very keen on cutting down the plastic spacers between the bottom part and the Arduino, I hard-wired the shield to the Arduino instead. It was necessary to remove the extension headers, the power connector and the ISP headers that were already populated on the Leonardo board. I subsequently connected the three pins that were relevant (5V, GND, D6) and two more (D7, SDA) to give the build more mechanical stability. Now the top cover fits nicely, and its two openings (that were initially designed to allow connecting pins to the Arduino) serve as ventilation openings for the emitted heat.