> OK. So I think I'm building my device using TTL, just so I don't *break* 
> the thing before it's finished. :-S

What are you making BTW?  Could you use one of those cheap micro controllers 
instead?

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>> OK. So I think I'm building my device using TTL, just so I don't 
>> *break* the thing before it's finished. :-S
> 
> What are you making BTW?  Could you use one of those cheap micro 
> controllers instead?

Is it actually possible to program a micro controller in such a way that 
it does what you expect it to?

It's an interesting idea, but it looks like the kind of thing where I'd 
spend the rest of my life wondering why it doesn't do what I thought I 
programmed it to do. (I.e., it looks impossible to debug.)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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> Is it actually possible to program a micro controller in such a way that 
> it does what you expect it to?

Ermmm, yeh, otherwise I'd doubt they'd sell many.

> It's an interesting idea, but it looks like the kind of thing where I'd 
> spend the rest of my life wondering why it doesn't do what I thought I 
> programmed it to do. (I.e., it looks impossible to debug.)

If you're thinking of making it from logic gates, it would seem like it 
would only be a very short program in any language.  Last time I used them 
was about 10 years ago and you had to do it in assembly.  But there was a 
simulator you could run your code on.  Nowadays I suspect they are far more 
sophisticated, I'm sure you can get a USB programmable one fairly cheaply, 
just google for "USB microcontroller".

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>> Uh... OK. I never did that before - but hey, maybe that's why half my 
>> circuits didn't work?
> 
> Hehe maybe, you certainly shouldn't assume that a not-connected or 
> floating input will be treated as logic 0.

Hmm... Oh dear.

>> Damnit, I thought digital electronics was just about on or off. :-/
> 
> It is if you follow the specifications of the particular logic family 
> you are using, IIRC TTL is something like 0-0.8V for logic 0, and 2.5V 
> and above for logic 1.

Really? I thought it was 4.5V - 5.5V for logic 1...

>> You speak of "3-valued logic" with it's "Hi-Z" mode?
> 
> I don't know what it's called, but I remember it when we were doing 
> simple memory circuits at university, you need to be able to output 
> either 0,1 or floating to the data bus.

http://en.wikipedia.org/wiki/Hi-Z
http://en.wikipedia.org/wiki/Three-state_logic

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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> Really? I thought it was 4.5V - 5.5V for logic 1...

http://www.twysted-pair.com/74xx.htm

Note that the output from one chip can actually only drive 10 inputs, I 
thought it was much higher than this but maybe I was remembering some other 
chip series.

> http://en.wikipedia.org/wiki/Hi-Z

Yes, exactly. Did you read the 2nd paragraph there? ;-)

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>> Really? I thought it was 4.5V - 5.5V for logic 1...
> 
> http://www.twysted-pair.com/74xx.htm

OK, that's interesting. Wikipedia claims

"All standardized common TTL circuits operate with a 5-volt power 
supply. A TTL input signal is defined as "low" when between 0 V and 0.8 
V with respect to the ground terminal, and "high" when between 2.2 V and 
5 V.[8]"

And yet, note [8] refers to the link above, which contradicts that 
statement. I'm confused...

> Note that the output from one chip can actually only drive 10 inputs, I 
> thought it was much higher than this but maybe I was remembering some 
> other chip series.

Well, I'm unlikely to reach even that number...

>> http://en.wikipedia.org/wiki/Hi-Z
> 
> Yes, exactly. Did you read the 2nd paragraph there? ;-)

Damnit, the whole *point* of digital electronics is to obviate the need 
for resisters and complex stuff like that. A digital circuit should just 
be an arrangement of logic gates, and nothing else! >_<

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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> "All standardized common TTL circuits operate with a 5-volt power supply. 
> A TTL input signal is defined as "low" when between 0 V and 0.8 V with 
> respect to the ground terminal, and "high" when between 2.2 V and 5 V.[8]"
>
> And yet, note [8] refers to the link above, which contradicts that 
> statement. I'm confused...

I think they just took the average of the minimum output voltage and minimum 
input voltage (2.0 and 2.4) to simplify things.

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Am Tue, 19 Aug 2008 07:32:37 +0100 schrieb Orchid XP v8:

> Is it actually possible to program a micro controller in such a way that
> it does what you expect it to?
> 
> It's an interesting idea, but it looks like the kind of thing where I'd
> spend the rest of my life wondering why it doesn't do what I thought I
> programmed it to do. (I.e., it looks impossible to debug.)

I'd suggest Atmel's AVR series, either ATtiny or ATmega, depending on the 
requirements, but I'd think a puny ATtiny13 will suffice. They're around 
1.50€ each and impressively well equipped (although only 5 I/O pins can 
be used, or 6 if you don't want to use the /RESET pin, which you probably 
wont - it's used for in-circuit serial programming).
Atmel provides an IDE with an assembler and a simulator, you can install 
a GCC variant for the microcontrollers too. 
I've built a simple music-box (out of an cheap MP3-player) with a motor 
for my baby-boy, with programmable run-time and motor-speed. All driven 
by an ATtiny13 and a C program. It's really enjoyable, so give it a try!

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Am Tue, 19 Aug 2008 04:50:45 -0400 schrieb Michael Zier:

>and impressively well equipped (although only 5 I/O
> pins can be used, 

That means: well equipped internally, obviously (timers, interupts, PWM 
generators, EEPROM for non-volatile data storage, RAM [so C can be used 
for stack-based programms] ... )

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> I'd suggest Atmel's AVR series, either ATtiny or ATmega, depending on the 
> requirements, (...)

I second that! The ATMegas are really great. I have build a 
radio-controlled alarm clock with an LCD and binary display.

Later we build an inverted pendulum as a university project (computer 
science), controlled by an ATMega88 (2.60$). Complete Board was around 30$:
http://www.inverses-pendel.de.vu

Next project will be a 8x8x8 LED cube. I've made some tests and I'm 
confident that an ATMega88 will be sufficent to control 512 LEDs at 
100Hz refresh rate, while still having recources to receive frames to 
display over a serial interface.

Manuel

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