andrel wrote:

> Ok, Andy, here is the deal: we trust Ken in this, you put one of these 
> books on your Amazon Wish list and you give me a link to that wish list. 
> In exchange, after you received it, you read it and you stop asking 
> questions that are answered in the book. Remember: Ken has also a copy.

My mother once said something to me, which I try to follow [although I 
don't always succeed]. She said "if you don't have anything nice to say, 
don't say anything".

If you think my questions are stupid or you don't feel like answering 
them, then fine. Don't answer them. Ignore the thread or something. But 
there's no need to make a point of telling me I'm stupid just because I 
*dared* to ask for a few pointers. OK?

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scott wrote:

> I was going to suggest he learnt about transistor basics (including the 
> analogue analysis of simple transistor circuits) before embarking on a 
> project using them - but you said it much better than I could :-)

The entire reason I find digital circuits interesting is that it avoids 
the bewildering complexities of analogue design. ;-)

(OK, that's a lie. I find computers interesting, and computers are digital.)

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Invisible wrote:
> If you think my questions are stupid or you don't feel like answering
> them, then fine. 

As has been said many times, the only stupid question is the one that is not
asked. Keep asking questions, Andrew, it's the best way of learning.
BTW We still reserve the right to say GIYF or even WIYF ;-)

John
-- 
Cogito sum,|| wbu### [at] tznvypbz (rot'ed) || GPG Key Fingerprint:
ergo sum,  ||   These opinions are mine alone,   || 0D9BCF4CF1B71CA2F5F7
cogito     ||     others can find their own      || BFBBCBC34EDEAEFCE453

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>> I was going to suggest he learnt about transistor basics (including the 
>> analogue analysis of simple transistor circuits) before embarking on a 
>> project using them - but you said it much better than I could :-)
>
> The entire reason I find digital circuits interesting is that it avoids 
> the bewildering complexities of analogue design. ;-)

Sure, but you should least have a basic understanding of the properties and 
characteristics of the transistors that you are using.  And especially if 
you are trying to wire up LEDs you should also get a basic understanding of 
simple LED circuits, ditto for switches and inputs.  It's not that hard and 
will make your life much easier when you start wiring up actual logic chips 
to do useful things.

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>> The entire reason I find digital circuits interesting is that it 
>> avoids the bewildering complexities of analogue design. ;-)
> 
> Sure, but you should least have a basic understanding of the properties 
> and characteristics of the transistors that you are using.  And 
> especially if you are trying to wire up LEDs you should also get a basic 
> understanding of simple LED circuits, ditto for switches and inputs.  
> It's not that hard and will make your life much easier when you start 
> wiring up actual logic chips to do useful things.

FWIW: I have owned a total of 3 different electronics kits as a kid. I 
have no difficulty wiring together arrangements of switches, LEDs, 
relays, and so forth. But all the manuals were a little vague on how 
transistors actually work.

(I'm actually pretty damned certain I had some 7400s, and I made useful 
circuits with them. But it was a long, long time ago now...)

Of course, when you buy a kit, somebody else has already figured out 
what kind of LEDs to put in there, and what resister you need to connect 
it to. I recall routinely using ICs to drive LEDs - but that was TTL, 
and now I'm looking at CMOS, which has different characteristics.

Anyway, we'll see what happens I guess.

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On 5/20/2010 10:29 AM, Invisible wrote:
> Mike Raiford wrote:
>
>> Unrelated, but tangential, How do you like LogiSim?
>
> Not very much.
>
> I mean, it *works*, but that's about it. It's really hard work to *do*
> anything with it. All gates default to having 5 inputs, no matter how
> many times you change it back to 2. All devices default to East
> orientation, no matter how many times you change it. Even just moving
> part of the circuit to make some room is quite unecessarily difficult.

Funny, it seems to get high ratings on SourceForge. ;)

But, yeah, all of your complaints are legitimate. Actually, if you click 
an item on the toolbar (And I hate the way the toolbar is tied to the 
project, BTW...) and change its attributes there, then it should stick. 
Pin labels on a subcircuit are a major PITA. IMO it should print the pin 
on the block (even if the block needs to be a tiny bit larger)

One thing that is particularly annoying is if you need a gate with an 
even number of inputs beyond 2: They don't exist. So, you wind up tying 
2 inputs together, then later (because you can barely see the wire 
connecting those 2 inputs) wind up wiring 2 wires together and getting 
an error.

> On top of that, the graphics look horrible, pin labels refuse to display
> when you need to see them, it's quite hard to label anything properly,
> and it spazzes out if you try to built a latch.

Yeah, it doesn't do too well with latches or flip-flops. I tried to 
build a J-K flip-flop in it, and it fell flat. Surprisingly the latch 
worked fine (Maybe because it was a NAND latch, instead of a NOR latch?)

Another nuisance that I've encountered a frustratingly large amount of 
the time is the "phantom wire", where you'll click somewhere to select 
something and a wire will appear out of what appears to be nowhere 
(usually connecting to half a dozen wires that shouldn't be tied together.)

Also frustrating is the lack of bidirectional pins for subcircuits. I 
started my design, and only when going out to the main block and 
wondering why the app didn't seem to pass signals out when I was asking 
for signals did I discover that inconvenient fact.

I'm not terribly concerned with how the application looks. It functions 
reasonably if you stay away from the caveats.

> But apart from all that, it works perfectly. :-}

It does the job, at least. It's somewhat better than the rest of the 
programs out there.

One thing the program truly needs is hotkeys. The way it is now requires 
excessive mousing.

Falstad's circuit sim seems a bit easier to use at times, and it's 
interface isn't stellar.

> As if the problem of designing complex arrangements of logic wasn't hard
> enough to start with...

Heh. A side project to this whole thing is writing my own logic 
simulator. I've got it at least moving signals from point a to point b 
reliably. I can modify wires and move things around in the program, but 
that's about it. My simulation model is different (from what I can tell) 
from Logisim, so I'm guessing the whole flipping out over oscillation 
and stopping the simulator may not happen. We'll see, but that's the 
trouble with feedback. ;)

Actually I'm quite happy with myself as far as my sim's UI code goes at 
the moment, even if it's extremely minimal. One of the issues I ran into 
was reconciling the pin connections from their locations. Walking the 
list of pins for each item's pin took a painfully long time once you had 
an appreciable amount of items on the board. My solution: a quadtree. 
This morning I filled the board up with over 100 wires, and with an 
average of 10 iterations it finds the nearest pin. As opposed to the 100 
iterations it would take before. Nice savings (it becomes important 
after moving an item, because the program checks that every pin is 
connected, and removes connections on any previously connected pins) 
Also, when dragging handles or items, the interface highlights areas 
where a pin will either split a wire or connect to another pin. Since 
this happens hundreds of times in the course of a drag operation, you 
get more than a few dozen items, and the UI gets sluggish.

I have the project on SourceForge (yeah, I'm going to do the entire open 
source thing with it. Why not?) But, contrary to their suggestions of 
releasing files on essentially day 0, I haven't released anything yet. 
Once I get more of the basics done, I'll do a preview release.

One of the things that would be nice is the ability to create a timing 
graph.

I also have a design goal of allowing the interface to be flexible. Such 
as allowing the user to assign hotkeys to items, giving a choice between 


We'll see if it turns out to be anything more than vaporware, though. I 
have a history of ethereal personal programming projects.

-- 
~Mike

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On 5/20/2010 3:20 AM, Invisible wrote:

> Now looking at <http://focus.ti.com/lit/ug/scyd013b/scyd013b.pdf>, on
> page 231 (which is actually page 236 of the PDF file), we see that for
> the 74HC00 I'm looking at using, we have Icc <= 0.02 mA, Iol = -Ioh <= 4
> mA, and tPLH = tPHL <= 27 ns. Now, if I actually knew WTF that means...

Icc sounds like the supply current, Ioh/Iol would be the currents the 
output is capable of sourcing or sinking, tPLH and tPHL would be the 
slew rate for the device (e.g. how fast it transitions from one state to 
the next)

-- 
~Mike

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>>> Unrelated, but tangential, How do you like LogiSim?
>>
>> Not very much.
>>
>> I mean, it *works*, but that's about it. It's really hard work to *do*
>> anything with it. All gates default to having 5 inputs, no matter how
>> many times you change it back to 2. All devices default to East
>> orientation, no matter how many times you change it. Even just moving
>> part of the circuit to make some room is quite unecessarily difficult.
> 
> Funny, it seems to get high ratings on SourceForge. ;)
> 
> But, yeah, all of your complaints are legitimate.

Too right! ;-)

> Actually, if you click 
> an item on the toolbar (And I hate the way the toolbar is tied to the 
> project, BTW...) and change its attributes there, then it should stick. 

I would literally have never thought of that.

> Pin labels on a subcircuit are a major PITA. IMO it should print the pin 
> on the block (even if the block needs to be a tiny bit larger)

That and the subcircuit label...

> One thing that is particularly annoying is if you need a gate with an 
> even number of inputs beyond 2: They don't exist.

Yeah, that too. Hello? It's software? It's not like with real hardware 
where it would *cost money* to have more sizes available. :-P

> Yeah, it doesn't do too well with latches or flip-flops. I tried to 
> build a J-K flip-flop in it, and it fell flat. Surprisingly the latch 
> worked fine (Maybe because it was a NAND latch, instead of a NOR latch?)

It's trying to be helpful by detecting circuits which are unstable.

Actually, I found a small hack: If you have, say, an RS latch and you 
configure the S pin to float low and the R pin to float high, it 
generally stops complaining. (Unless something really *is* wrong...)

> Another nuisance that I've encountered a frustratingly large amount of 
> the time is the "phantom wire"

Yeah. The whole wiring concept is just awkward. For example, Reactor 
(which has nothing to do with electronics but does involve wiring things 
together) has wires that go in a straight line from pin to pin. And when 
you move stuff, IT DOESN'T BREAK ALL THE WIRES OR RANDOMLY CONNECT THEM 
TO OTHER PINS! Sheesh, it's not rocket science...

> Also frustrating is the lack of bidirectional pins for subcircuits.

So far I haven't found this to be a problem.

> I'm not terribly concerned with how the application looks. It functions 
> reasonably if you stay away from the caveats.

I'd prefer something less ugly to look at, personally.

>> But apart from all that, it works perfectly. :-}
> 
> It does the job, at least. It's somewhat better than the rest of the 
> programs out there.

KLogic was easier to wire up. And it could do simulation graphs, which 
is extremely useful when you're trying to check, e.g., that your flip 
actually flops on the rising edge.

On the other hand, KLogic crashes constantly, and sometimes gives you 
blatently incorrect results, which is far, far worse than merely being 
difficult to use.

> One thing the program truly needs is hotkeys. The way it is now requires 
> excessive mousing.

It already *has* keyboard shortcuts for selecting different gates and 
stuff. What are you asking for?

> Falstad's circuit sim seems a bit easier to use at times, and it's 
> interface isn't stellar.

Which one?

> Heh. A side project to this whole thing is writing my own logic 
> simulator.

I also considered doing this. It would be nice to be able to concentrate 
on building logic rather than working around the limitations of some tool.

> I've got it at least moving signals from point a to point b 
> reliably. I can modify wires and move things around in the program, but 
> that's about it. My simulation model is different (from what I can tell) 
> from Logisim, so I'm guessing the whole flipping out over oscillation 
> and stopping the simulator may not happen. We'll see, but that's the 
> trouble with feedback. ;)

The reason I haven't attempted this yet is that I have literally no clue 
how to do something as complex as registering arbitrary mouse clicks and 
drawing sophisticated graphics in response. (E.g., how the hell do you 
figure out what the user just clicked on? Usually I let the toolkit sort 
that out - but this doesn't work if you draw everything yourself.)

> I have the project on SourceForge (yeah, I'm going to do the entire open 
> source thing with it. Why not?) But, contrary to their suggestions of 
> releasing files on essentially day 0, I haven't released anything yet. 
> Once I get more of the basics done, I'll do a preview release.
> 
> One of the things that would be nice is the ability to create a timing 
> graph.
> 
> I also have a design goal of allowing the interface to be flexible. Such 
> as allowing the user to assign hotkeys to items, giving a choice between 

> 
> We'll see if it turns out to be anything more than vaporware, though. I 
> have a history of ethereal personal programming projects.

Join the club. ;-)

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On 5/20/2010 3:38 AM, scott wrote:

>
> The HC series can sink and source up to 4 mA on the output pins if you
> want the signals to still be valid (eg for input to further logic
> gates). If you are just using them to drive LEDs then apparently up to
> 20 mA is OK.
>

So long as the voltage doesn't sag below the forward voltage for the LED 
it should be OK. I think at that current it will barely be able to drive 
an LED.

-- 
~Mike

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On 5/20/2010 12:14 PM, Orchid XP v8 wrote:

>
> Datasheets aren't manuals. They assume that you already know what, say,
> a Gated D-Latch is, and that you just want to know what its maximum
> driving current is or something. If you *don't* already know what a
> Gated D-Latch is, the datasheet will be of no use at all. You need
> *real* instructions.
>

Many datasheets will give you a truth table, and some even have 
schematic diagrams. They assume a basic understanding of electronics, 
though.


>> Have you ever looked at e.g.
>> http://en.wikipedia.org/wiki/File:TTL_npn_nand.svg ?
>
> 1. What is this thing?

A TTL NAND gate

>
> 2. How does it help?
>

You should be able to see why the input floats high from the schematic.

-- 
~Mike

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