>> Dude, really, you are going to fall over yourself over and over again if 
>> you refuse to learn at least some basic analogue circuit electronics. 
>> You must have realised by now that even to implement the simplest logic 
>> circuits you absolutely must have some basic level of understanding.
>
> So what you're saying is that there is basically no way I will ever get 
> this to work, and I should just give up now?

No, you can probably get this circuit to work by experimenting yourself, 
asking here and googling.  Some people might even be nice enough to give 
some detailed explanations, and you might learn some stuff.  You might even 
be able to get a slightly more complex circuit to work ok.

But in the end you're doing things backwards, learn the basics *first*, it 
will make your life so much easier, and you won't get stuck at every point 
when things don't work as expected.  You will be able to answer your own 
questions if you have the knowledge of how basic electronic circuits work.

For example the next thing will be relays to control things that need higher 
power or voltage, you're going to connect one of your outputs to a relay 
coil and then wonder why it's not working, and then complain that the relay 
is destroying all your ICs :-)

Post a reply to this message

scott wrote:

> But in the end you're doing things backwards, learn the basics *first*, 
> it will make your life so much easier, and you won't get stuck at every 
> point when things don't work as expected.  You will be able to answer 
> your own questions if you have the knowledge of how basic electronic 
> circuits work.

Funny, I thought I *already* had a basic knowledge of how circuits work...

I guess what's throwing me is this new "logic low = negative" thing. I'm 
used to thinking of logic low as "nothing connected here". If you were 
making a bunch of logic out of switches with either connect or don't 
connect a wire to the positive rail, everything would be quite a bit 
simpler. (E.g., connecting the output of two gates together couldn't 
possibly create a short-circuit condition, since each output is 
connected to the same battery terminal or to nothing at all.)

I guess I'm still trying to get my head around all the consequences of 
that. For one thing, it looks like every single [external] input and 
output is going to end up needing a resistor on it. Yay. :-/

> For example the next thing will be relays to control things that need 
> higher power or voltage, you're going to connect one of your outputs to 
> a relay coil and then wonder why it's not working, and then complain 
> that the relay is destroying all your ICs :-)

Uh, no, even I'm not crazy enough to want to do that. :-P

1. I'm turning LEDs on and off. What the hell do I need relays for?

2. Relays are comparatively expensive.

3. Relays presumably use about 100x the current that an IC can supply.

4. PROFIT!

5. Relays move vastly slower than even the slowest electronic logic 
gate. Why bother?

Post a reply to this message

> Funny, I thought I *already* had a basic knowledge of how circuits work...

The circuit diagram you posted here makes it look like you don't.

> I guess what's throwing me is this new "logic low = negative" thing. I'm 
> used to thinking of logic low as "nothing connected here".

OOC why are you used to thinking that?

> If you were making a bunch of logic out of switches with either connect or 
> don't connect a wire to the positive rail, everything would be quite a bit 
> simpler. (E.g., connecting the output of two gates together couldn't 
> possibly create a short-circuit condition, since each output is connected 
> to the same battery terminal or to nothing at all.)

This doesn't work, because as soon as you connect a "not connected" output 
to something, it becomes "connected" and will have a specific voltage.  The 
severely limits how many things you can connect to a single output.

> Uh, no, even I'm not crazy enough to want to do that. :-P

It was just an example, you might one day want to control a motor, a 
brighter lamp or a heater or something.

> 3. Relays presumably use about 100x the current that an IC can supply.

Hehe no, I've got a tiny surface mount IC here that is driving 6W of LEDs 
directly.

> 4. PROFIT!

Huh, what are you planning to sell? No more free advice :-)

Post a reply to this message

>> Funny, I thought I *already* had a basic knowledge of how circuits 
>> work...
> 
> The circuit diagram you posted here makes it look like you don't.

Well, I noticed it wasn't going to work *before* I assembled it, right? ;-)

>> I guess what's throwing me is this new "logic low = negative" thing. 
>> I'm used to thinking of logic low as "nothing connected here".
> 
> OOC why are you used to thinking that?

I guess it's the way most books refer to circuits as "on" or "off". 
Usually if something is "on" it means it's connected to a power source, 
and if it's "off" then it isn't connected. That's how, e.g., a light 
switch works. It doesn't connect the output to the other pole when you 
turn it off, it just doesn't connect it to *anything*.

Of course, strictly speaking, logic high and logic low can be 
_anything_. So long as it's documented what they are and all the 
circuitry is expecting the same thing, it'll work. But still, most 
people casually refer to "on" and "off".

>> Uh, no, even I'm not crazy enough to want to do that. :-P
> 
> It was just an example, you might one day want to control a motor, a 
> brighter lamp or a heater or something.

Fair enough. But my immediate plans only run to wiring up lots and lots 
of logic gates, and observing their output.

>> 3. Relays presumably use about 100x the current that an IC can supply.
> 
> Hehe no, I've got a tiny surface mount IC here that is driving 6W of 
> LEDs directly.

Sure. But I'll bet it isn't a general-purpose logic gate. It'll be some 
special driver IC or something.

>> 4. PROFIT!
> 
> Huh, what are you planning to sell? No more free advice :-)

OOC, what's your hourly rate?

Post a reply to this message

On 5/25/2010 6:33 AM, scott wrote:

>> 3. Relays presumably use about 100x the current that an IC can supply.
>
> Hehe no, I've got a tiny surface mount IC here that is driving 6W of
> LEDs directly.
>

It's more about the relay's coil being an inductor. Once the IC 
switches, it will send a high voltage pulse back through the IC, frying 
it nicely. There are ways to get around that, but I'll leave that as an 
exercise to the reader to figure that out.

Hint: The circuit simulator has an example of this. :)

-- 
~Mike

Post a reply to this message

> It's more about the relay's coil being an inductor.

This was exactly the point I was trying to make, that wiring up a relay 
would "seem" to work (assuming your IC could source enough current) but then 
in reality it's going to blow the IC :-D

Post a reply to this message

Mike Raiford wrote:

> It's more about the relay's coil being an inductor. Once the IC 
> switches, it will send a high voltage pulse back through the IC, frying 
> it nicely. There are ways to get around that, but I'll leave that as an 
> exercise to the reader to figure that out.

More importantly, if the *whole* circuit is relays, there's nothing to 
fry. ;-)

(Other than your electricity bill, anyway...)

Post a reply to this message

> Sure. But I'll bet it isn't a general-purpose logic gate. It'll be some 
> special driver IC or something.

Of course, same as your hex buffer you mentioned.  But you still can't 
connect a relay directly to it without risking damage to the IC (as Mike 
explained).

> OOC, what's your hourly rate?

How much you got?

Post a reply to this message

>> Sure. But I'll bet it isn't a general-purpose logic gate. It'll be 
>> some special driver IC or something.
> 
> Of course, same as your hex buffer you mentioned.  But you still can't 
> connect a relay directly to it without risking damage to the IC (as Mike 
> explained).

And I still wouldn't try it in the first place. ;-)

>> OOC, what's your hourly rate?
> 
> How much you got?

I think we can take it as read that it's peanuts compared to what you 
usually make. ;-)

Post a reply to this message

>>> OOC, what's your hourly rate?
>>
>> How much you got?
>
> I think we can take it as read that it's peanuts compared to what you 
> usually make. ;-)

So?  Depends how fun it is.  If you wanted me to test drive Ferraris then 
you needn't pay me very much :-)

Post a reply to this message