Hey, Patrick,
I've just got my hands on a couple of real cool serial devices that I'd like to hook up to the Empeg. Including GPS (don't have quite yet...), I'd like to add 3 peices of hardware to the serial port. Any updates on your PIC-based IO board? I'd deal with a multi-drop serial board if I could find any relatively small, external devices. So far, the closest I've come is a multiplexor, but those things are ancient, big, and not cheap. I still think an address-based microcontroller that can switch between 3-4 serial ports on demand (1-Byte header or something) would be great, but if there can be any more devices (a/d, d/a, whatever), that's just icing!

Anyone got aspirations to build such a beast? I'd be happy to pay for the hardware, and some of the development (the closest I ever got to this was building a parallel port-controlled robot).
Thanks,
Jason

_~= Dearing =~_
"WAY too happy about having #99."

Building a device to multiplex the serial port should be trivial. The hard part (which really isn't all that hard) would be getting the player to decode a header byte and handle the data appropriately. The only issue that I can think of is if two devices want to communcate at the same time to the player, one of them is going to not get their data acroos unless they are waiting for a "go ahead and give me your data" message from the multiplexor. This is doable, provided that the devices that are sharing the serial port can be custom programmed to wait until its their turn to transfer data.

The control would be very simple in that case:
1) Send "its your turn" signal to device 1
2) Recieve data from device 1
3) Transmit data that was recieved from device 1 to the player
... repeat for every device

Actually constructing the HW and the PIC SW would take me about 15 minutes to design, but due to the simultanious transfer problem, I haven't found it to be a particualrly useful application.

(note, my experience at the hardware level is limited, so just ignore this if it's completly off)

Couldn't you build the multiplexor to support flow control? If one device is transmitting or recieving, toggle the flow control on the other devices to have them wait until the line to the empeg is open. This should work with more devices compaired to trying to deal with custom programming on every serial device that might sit on the multiplexor.

I'm in the process of throwing together such a beast. Here's how I'm going to tackle the problem:

The devices we are talking about interfacing too are low data rate, 4800 and 9600bps (GPS and OBDII) and that's not even continuous. The empeg can handle much more than that.

The multiplexor can buffer the communications and send a whole 'line' at a time to the empeg and back again. Each line gets prefixed to indicate what device it's from/to.

Additionally, an option may be needed to enable/disable specific streams. (I don't know if OBDII needs long bursts of data yet.)

My plan is to build a board that supports two serial devices (GPS and OBDII) as well as providing an accelerometer for basic rally computer functionality (0-60 time, 1/4 mile, peak HP, that kind of thing.)

If it's not too much effort, how about a couple ADC's, temp sensors, or other Analog inputs? How many devices is your new serial protocol going to support?

That all depends on which micro I end up using and how much space/CPU time is left. I expect to be pretty much maxing out the latter on a 16F877.

However, there's no reason the protocol can't be used on different boards or that devices that don't interest you are replaced (with a different ID) on a specific board.

Digital temp sensors are easy to hook up if you don't need better than 1C/2F resolution.