BX-24 Expanded IO and RAM using I2C Interface
D & B Howey
The reduced IO and lack of external RAM for the BX-24 can be easily
accomodated with external chips.
If you need more digital IO add one or more Philips Remote IO expanders with
I2C interface for 8 digital IO's with an interrupt option (PCF8574, $8.55
CDN). If you need more RAM, add one or more Philips Clock/RAM chips with I2C
interface for 256 bytes of RAM if you don't use the clock feature. (PCF8583,
$11.44 CDN).
The I2C interface only uses 2 digital IO to interface to multiple devices. A
third IO line can be used to implement an interrupt from the IO expander. It
is actually quite easy to program the I2C interface. I ported some C code
posted by www.phanderson.com.
I have tested this approach on a breadboard and am now wiring up a small
"Lego brick" controller with 24 IO, 656 bytes of RAM and a dual H bridge
motor controller (L293D). This controller has the same footprint as a 4 AA
cel battery holder. It includes individual Molex connectors for all external
devices including power and ground on each connector. External devices will
include infrared distance ranging (Sharp GP2D02), ultrasonic distance
ranging (Polaroid 6500), electronic compass, 4 servos, 2 Lego gearmotors,
bump switches, 2 odometers, battery level, IR remote control receiver. Other
features include an RJ-11 serial programming/control connection, power
switch, 5V regulator and an external power jack and a power on LED. This
homebuilt controller brick will ride on a dual track undercarriage built
using a small Lego Technic tracked car. I expect "Lego Mindstorms" on
steroids.
The BX-24 is an excellent choice for an adventurous robotics beginner. The
I2C expansion chips will of course work with most any microcontroller.