Dan, the board looks good but I think you will find that a 40-Pin PIC
really does not have enough I/O if you want to add several sensors. Right
now I'm using separate PICs for functions like the IR sensors, Compass,
Range finder, H-Bridge control, and speech I/O. I'm also looking at adding a
CPLD for extra I/O. One of the Lattice CPLDs I did provides 16 Inputs and
Outputs using an SPI-style interface. It's basically four shift registers in
a single package with some expanded control functions.

   While I've been focusing on testing sensors and have not finished the
overall architecture, the 16F877 core interface looks like this:

   PortA = 4 A/D channels, +Vref, and Right Tach Input (TMR0).
   PortB = Interrupt expansion. Uses an external 74HC30 and RB0/INT to
           provide 7 interrupts; 2 bumper switches, 3 IR, and 2 spares
           reserved for Rangefinder and Speech Input PICs.
   PortC = RS232, 5 SPI chip selects, Left Tach Input (TMR1).
   PortD = Dual Motor control for the H-Bridge PIC, 4 spares.
   PortE = SPI

   This makes it easy to add custom `smart modules' and frees the main CPU
to concentrate on higher functions. If I wired directly to the 16F877, I
wouldn't have enough pins and CPU resources.

   I'm looking at how much I can combine in a small CPLD. Things like motor
control, PWM, 40KHz source with three gated outputs for IR and Rangefinder,
interrupt expansion, additional I/O, etc. I'll let you know if it develops
into anything useful. Maybe we can look at another board downstream.

   - Tom

At 04:09 PM 5/3/01 -0400, Dan Michaels wrote:
>>How does LCD connect? Just use a dedicated digital
>>IO port??
>
>Ummm - there aren't enough pins on a PIC40 to add an LCD and still
>have all the other stuff that I have here. However, I "could"
>leave out the ULN2803 and put in an LCD, but .........
>
>Unfortunately, you can only push 40 pins and a small pcb and
>not-smt and still cheap just so far. There's lots of other things
>I wish I could put on there, but ...........
>
>Actually, the idea is to have a basic standalone controller board,
>and also the possibility to stack another SBC on top for additional
>things, and talk between the two via RS-232 - using subsumption
>architecture techniques:
>
>best regards,
>- Dan Michaels
>www.oricomtech.com


------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

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