iOS Sensor Apps with Arduino

Connecting to the Arduino

While the original Arduino board used RS-232 serial to connect to the development machine, more recent models use USB. We therefore need an adaptor to translate from RS-232 serial used by the Redpark cable to the TTL serial that we can easily connect to the Arduino transmit/receive (TX/RX) pins (pin 1 and 0, respectively).

To do this conversion I’m using the SparkFun RS-232 Shifter (see Figure 2-4; http://www.sparkfun.com/products/449; $13.95), although any equivalent unit would suffice. For instance, the Maker Shed carries the equally effective but slightly cheaper ($7) P4 Adapter Kit.

Figure 2-4. The SparkFun RS-232 Shifter SMD (sku: PRT-00449)

As you can see from Figure 2-4, the TTL end has four wires: RX, TX, GND, and VCC (5V). The easiest way to connect this to our Arduino is to solder some snapable header pins to four lengths of single core wire (see Figure 2-5) and build a custom jumper cable (see Figure 2-6). You can, of course, just make use of premade jumper cables; the Maker Shed, for instance, sells a set of Breadboard Jumper Wires that you could use instead of soldering up your own cable.

Figure 2-5. Single core wire (top) and snapable header pins (bottom)

Figure 2-6. The completed jumper cable

Once you have bought or built your jumper cable, connect ...