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DPRG: Real good riddle.

Subject: DPRG: Real good riddle.
From: Kipton Moravec kmoravec at airmail.net
Date: Sun Jul 27 18:30:36 CDT 1997

Let me add to what Kevin said.


Kevin Ross wrote:
> 
> > Another Q:
> > > Serial Cable (MAX232 + connectors = $5) <- what do you mean "MAX232 +
> connectors"(will I have to but the connector together on my own ?)
> 
> Yes.
> 
> > Another Q:
> > Will I have to make my own programmer or is tehr eon you can buy ?
> > (since my budget is really  tight I don't really want to fry several
> > chips before realizing that one pin in my programmer is connectred wrong)
> > I have heard stories that some people have messed up their computers by
> > connecting something "mistakenly"
> > And a LAST THING.
> 
> You program the 68HC11 with via the serial port. All you need is a serial
> port adapter, which is a MAX232 RS-232 <=> TTL converter. That is one of
> the advantages of the 68HC11. The specialized hardware is not required,
> other than the level shifter which you can use on any CPU.

I am guessing, by your questions, that you still don't know what Kevin
is saying. 

In general, the microcontrollers/microprocessors that have serial ports,
output the serial data with TTL (transistor - transistor logic) levels. 
A 0 is < 2.3 V and a 1 is > 2.7 V. (if those are not the exact numbers,
it is close enough for discussion.)  Maximum voltage is 5 V, Minimum
voltage is 0 V. This is fine if you are not going too fast, or too far. 

What happens if you want to go up to 200 feet?  TTL may do it, but not
very reliably without special wire.  There is a standard called RS-232
that specifies a different signal level for logic level 0, and logic
level 1.  These higher values (up to about 15 V I think) allow the
transmission of the data to go farther.  The minimum number of wires is
3, transmit, receive, and ground.  Often there are more wires for
handshaking.  You see these mostly in modems, and higher speed
connections. 

So how do you convert the microcontroller's TTL signal to RS-232?  That
is where the MAX232 chip comes in.  It is very inexpensive <$2 I think.
(I have not purchased one.)

To make the discussion complete, there is another serial standard called
RS-422.  It has the advantage of going up to 4000 feet. It takes 2 or 4
wires depending on if you want half-duplex or full-duplex.  Half duplex
means only one side can talk at a time, like a CB radio.  Full-Duplex
means both sides can talk at the same time, like the telephone.  Why 2
wires each way? Because it uses a technique where it measures the
difference between the wires.  They twist the wires so any signal noise
>from outside sources hits both wires the same, so it either adds or
subtracts the signal from both wires.  On the receiving end, they look
at the difference between the wires, and any noise added to both wires
identically is subtracted out! 
There are interface chips for the RS-422 standard also just like the
MAX232.  They cost under $4 too. 
 
> 
> > GOD DAMN THIS PROCESSOR IS 40 pinner. Hell I don't know if you ever heard
> > it: " If you can't afford to blow it up, then don't use it at ALL"
> 
> Huh? What 40 pinner?  The 68HC11 usually comes in a 52-PLCC configuration.
> You typically put it in a socket on a development board like a BotBoard I.
> 
> I have yet to see anyone blow up a 68HC11. It would be interesting. Your
> quote about blowing things up sounds quite macho, but is very poor advice.
>
Well, I can't afford to blow up my PC, but I use it a lot!  I have two
of them running 24 hours per day, seven days per week.  When I am not on
them, they are running a program, trying to prove if certain very large
numbers are prime or not.  My NT machine is looking at 2^3052937-1 at
the moment (If you would write that number in decimal in a typical
paperback book, it would take over 250 pages.  It will take 2-3 weeks to
find out if that number is prime or not.

Well what about your car?  Can you afford to blow it up?  Or do you
walk? :) In my opinion, it is bad advice.
 
> 
> > I am simply little bit afraid that I would spend my money and the first
> > this I'll see from that processor would be a grey smoke. The first thing
> > I would attempt would be probably a LED sequencer. IT is like writing
> > "Hello Wolrd" when yo uare learning new computer language.
> >
> > I'm sorry for so many questions but you see I'm about to spend my money
> > on something  and there you are telling me that I shoudl reconsider what
> > I'm doing (TRUST ME I have nothing against it ...in fact it might be even
> > a blessing before I would go bald trying to figure things out)
> 
> You need to decide at what level you want to jump in. You can get
> completely packaged solutions for any problem if you want to spend enough
> money. Or, you can buy the individual parts and put it together on your
> own.
> 
> Kevin

I would not get too worried about blowing anything up.  I accidently
mixed up power and ground on a 7476 TTL chip, (My robotics book had them
mixed up!) For some reason, they were on different sides of the chip
than traditional TTL chips.  The chips did not put the right output and
got pretty hot while I was trying to figure which logic pin I had wired
wrong.  After switching to the TTL logic book, to step through the logic
table, I realized the error, changed the polarity and it worked! I do
not recommend trying this at home (I am a professional <grin>). If it
didn't I would have been out the $0.33 I paid for the chip. (Big deal.)

The most likely place to cause problems is with static electricity.  You
can generate 200 V of static electricity, and when you touch something,
you discharge it, and not even know it!  It takes about 400 V of static
electricity before you feel the shock. 

So take some precautions when handling the boards, and you will be O.K.

A couple of days ago, I had sparks fly when my +12V power line popped
off my board and landed on the 12V return.  The wire got hot, but the
flying sparks alerted me to the problem, and I was able to move the wire
in under 2 seconds before anything was damaged. (It is amazing how
flying sparks can wake you up to a problem quickly.) :)

What you need, is a couple of electronics guys nearby that can help you
get started.  Once you see how simple it really is, you should be in
good shape.

I have been thinking of hosting a monthly GTG for the DPRG, where people
can come and help or get help with their projects. I have a good table
saw, and some other tools for helping build their robot. Perhaps, what
one person needs, is someone to show them how to solder, so they can get
started building their board.  Perhaps another needs some help getting
started with assembler.  Perhaps another needs help getting his acoustic
ranging sensor to work.  DPRG has a lot of people with a lot of
different talents.  This is a way everyone can get help in areas where
they are not so strong. Is this something of interest for the DPRG
people?

Regards,
Kip

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