Subject:
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Musings regarding Handyboard Expansion & Interfacing
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 6 Aug 1996 12:45:55 GMT
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Original-From:
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Brian Lavery <{blavery@acslink.aone.net.au}Spamcake{}>
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Viewed:
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1648 times
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I have been playing with my Handyboard (from Digital), and am still
waiting on the little mobile platform I decided to start out on.
(My retired father-in-law is a mechanical creator, & is PC literate,
so I am planning on getting him involved after he sees some of
my first attempts doing smart things!)
At this stage, most of my effort is just THINKING & planning.
The platform may be easier to upgrade in future than the PCB &
sensor parts of the robotics. So developing a vision for which way
to go in developing the H/B seems a good investment of effort.
Anyway, I thought I would share some of my ruminations & musings
Maybe it might provoke some good cross-ideas. Here goes ....
********************************************************
* MUSINGS ON THE SUBJECT OF HANDYBOARD INTERFACING *
********************************************************
* Some assumptions & basic thoughts: *
********************************************************
1. Eventually, a LOT of I/O can be needed. The Handyboard motherboard
has quite limited I/O, and expansion will be needed. Digital output
particularly is totally deficient.
2. Expect that anyone else's expansion system (even Fred's) will never
suit enough what I may want, so custom expansion must lie ahead
somewhere. Good thing that a standard 1/10 pitch is used for
all connector alignments. Hand-built expansion is feasible.
3. Dont consume I/O for wrong reasons - eg motor outputs for sonar.
4. Re: hobby servo drives. With the availability of the cheap Mini-SSC,
where the ongoing overhead of servicing the servo pulses is offloaded
away from the 68HC11, then any thought of driving the servos directly
from the Handyboard's I/O goes right out the window.
5. Driving the Mini-SSC needs an ASYNC output. Output async traffic
should be light. Maybe an OC output will cope?
6. Dont pre-empt the proper use of the SPI interface.
It can be handy for Vector compass, or other special functions.
And as an I/O method, it can be so much faster than the async comms.
7. However the SS line of the SPI could be sacrificed (into a GP output)
as using SPI with the 68HC11 only in MASTER mode seems reasonable.
8. The 3 output Chip Select & 3 input ones (Y0-Y5) will quickly be all
consumed unless we take some precautions to further subdivide them.
9. Two wheel encoders will likely take two IC type inputs. (If we use
quadrature inputs for 2 wheels, the 90 degree inputs can be
serviced by plain digital inputs.) Hey, we are running out of
high quality I/O !!!
10. Why did the Handyboard consume OC5 just for piezo output ????
OC5 can double as IC4 (timer input), and that ability is now
wasted. Might be a smart thing to physically patch the H/B
to exchange OC3 and OC5, ie, patch OC3 across to the piezo, and
put the OC5/IC4 pin to the expansion bus.
If PA7 is also picked up by an expansion board somehow, then a
much more capable I/O suite (PA pulse accumulator, IC timer capture,
OC output compare) is available. With a bit of hardware
multiplexing to drive these into a number of services, ... well now
we could be getting somewhere.
11. The multiplexing of analog inputs as per the Mark-One Fred Martin
expansion board seems perfectly fine, & worth just copying if a
custom expansion is built.
12. Fred's PIC on-board (expansion Mark-One) - not for me. In general,
however, I/O that needs extensive CPU resources is best got
off the Handyboard motherboard. That is why Scott's Mini-SSC is
an ideal servo interface.
13. Any expansion board probably begs the question of MORE expansion.
So thought is needed on what signals to pass thru to a further stage
of exp board. Eg A0-A7? CS subdivisions? Analog & smart
digital I/O (OC/IC) for further multiplexing? SCI/SPI?
Of course, we need to feed thru the LCD connections so the LCD
panel can sit on top.
14. Direct stacking of expansion boards means probably losing some
surface real estate each layer, as allowance at the edges may need
to be left for I/O connectors. (I/O is what I/O boards are for!)
See how Fred's Mark_One expansion board is shy of the motherboard
edges on the South & West edges.
So when do we opt for ribbon cable connections?
What are we trying to achieve?
==============================
Just getting a robot to move, and to respond to a minimal obstacle
detector, seems a pale shadow of the excitement that a robot should
be giving us. Surely our hobby is to create something really smart?
(Assuming your robot is a hobby!)
INTELLIGENCE requires AWARENESS in order to process.
AWARENESS requires SENSORS.
More sensors (hopefully) should give better awareness.
INTELLIGENCE requires ABILITY TO ACT in order to be useful.
ACTION requires OUTPUT DEVICES.
We want to see our bot doing smart things.
Conclusion - adding I/O, and then programming the brains to process
all the "I" into the best "O", is surely what amateur robotics must be
all about.
Bulk Sensors need bulk I/O:
===========================
Everett's "Sensors for Mobile Robots" shows what an "aware" robot might
use for sensing its environment.
See P.72 - Robot "ROBART 1" had several infrared proximity sensors, a number
of tactile bumpers, tactile feelers, sonar, tactile strips.
See P. 230 - "MDARS" type robot had 24 polaroid ultrasonic transducers, 48
passive i/r motion detectors, 6 microwave detectors.
Maybe the HandyBoard does need some expansion!
*********************************************************************
*********************************************************************
I've got some specific circuit ideas, but let me put them together in
the next day or so.
Footnote:
Shipping fee of my H/B from USA -> Australia was one cost, but
import duties here added about another US$70. Ouch.
Brian
------------------------------- ------------------------------
Brian Lavery B.E. MACS <blavery@acslink.aone.net.au>
Technical Manager - Systems (Also Compuserve 100232,622)
Mobex Pty Ltd Sydney Australia Tel +61 (2) 370-9250
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