Connecting the CF-III
Any sound system that responds to my droid sound command language and can handle a serial connection at 9600 bauds will work with the MarcDuino. One such system is the CF-III Sound loaded with my program as described here. It is an older and pricier sound setup than with the Sparkfun MP3Trigger, but it has the advantage of having a nice integrated amplifier in a clean package. Since the interface is real 12V level RS-232 signals (instead of the 5V UART version that the board speaks natively), it requires a bit of work to connect to the MarcDuino.
Note that the MarcDuino must be loaded with a the Master firmware image specific to the CF-III system (found here).
RS-232 Level Adapter
A level adapter is needed between the UART 5V level interface of the MarcDuino and the 12V RS-232 interface of the CF-III sound.
The cheaper ones, like the ones from SparkFun, tries to steal their negative power supply from the RS-232 link, and will not work with the CF-III.
Here is how to connect it to the MarcDuino v1 running v1 Firmware. If you run v2 Firmware, the blue wire would go to PC1 instead of PC4.
Older CF-III Systems (with Female DB9 Connector)
Until recently, the CF-III sound had a female DB9 connector. Two ways to connect them:
Using a Null-Modem cable
If you can find a null-modem adapter cable with male ends on either side, you are all set. However, I could not find a commercial one. Most male to male have an standard Rx to Tx twist and are not null modems. Extensions are null-modems, but male to female. So I had to make my own, starting with a male to female extension and replacing the female end with a male. Connect the level adapter to the MarcDuino as shown further down, and your male to male cable between that and the
Using DB9 male-male gender changer
That allows to simply plug the level adapter right into the CF-III, which is nicer. However you need to switch the J2 jumper inside the CF-III.
Then open up the unit, and change the orientation of the jumpers next to the serial port so they are perpendicular to the IC nearby:
Plug the gender adatper in the CF-III serial socket, then the Sparkfun level adapter into the gender adapter.
Recent (after late 2013) CF-III Systems (with Male DB9 Connector)
Recent systems (as of Sept. 2013) have a different serial port configuration. The socket in the CF-III has been changed to male, which is good, but the jumpers have disappeared (and left in the wrong default configuration), which is bad.
The boards now look like this, no headers or jumpers on JB2, just empty holes:
Use a Null Modem cable adapter
Use a regular Null Modem cable with female ends, and add a male to male DB9 gender adapter. It looks like this:
Using just the RS-232 adapter
If you are comfortable to modify the board and re-install the jumpers, you can dispense with both the null modem cable and the gender adpater. This leads to a cleaner installation.
You'll first need to sever the two traces on the back of the circuit board between the pins of the jumper. The traces were added as a permanent connection instead of the previously modifiable jumper configuration. We need to get rid of them for the jumpers to work.
I used a light application of a Dremel cutting wheel to cut the two traces off:
Then install the missing headers in JB2 on the other side and jumper it like below. Now just plug the level adapter straight in, nothing else necessary.