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Stephen wrote:
> I think that you've forgotten that electromechanical relays themselves contain
> several components. The coil, the former, the armature, the contacts and don't
> forget the back EMF diode.
True. But you purchase "a relay" and it already has all these parts
assembled. If you purchase "a transistor" you still apparently have to
connect half a dozen other components to it before it will do anything
interesting. ;-)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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OK, so does anybody know the difference between a TTL logic gate and a
CMOS logic gate?
I mean, *obviously* they make 'em a different way. But I don't make
logic gates - I use them. Is there any difference visible to the end-user?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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On Mon, 18 Aug 2008 12:45:13 +0100, Invisible <voi### [at] dev null> wrote:
>OK, so does anybody know the difference between a TTL logic gate and a
>CMOS logic gate?
>
>I mean, *obviously* they make 'em a different way. But I don't make
>logic gates - I use them. Is there any difference visible to the end-user?
TTL is slower and uses more power.
I once built a clock out of TTL, in the mid 70's it used IIRC 50 amps at 5 Volts
Vcc. A couple of years later a CMOS clock ran from a PP3 battery
--
Regards
Stephen
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> Ah, OK. If you want bipolar then yes, you'll need more relays. I'm used to
> playing with TTL circuits where if you connect it to V+, that's 1, and if
> you connect it to thin air, that's 0.
Err no, in TTL with BJTs, a floating input is usually pulled up to V+ inside
the chip, but this is not guaranteed so your inputs should never be floating
(always tie unused inputs to either V- or V+). *Outputting* a floating
signal is just a disaster is normal logic (there is nothing to stop some
very small amount of interference driving it high), and usually only used
where you need to have more than one output connected to the same line (eg
the data bus inside your PC - each connection to it should be able to output
low, high, or not-connected).
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Stephen wrote:
> TTL is slower and uses more power.
> I once built a clock out of TTL, in the mid 70's it used IIRC 50 amps at 5 Volts
> Vcc. A couple of years later a CMOS clock ran from a PP3 battery
50 amps? Shouldn't that tend to cause wires to melt and so forth?
Hey, isn't CMOS that stuff that breaks if you get static on it?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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>> I'm
>> used to playing with TTL circuits where if you connect it to V+,
>> that's 1, and if you connect it to thin air, that's 0.
>
> Err no, in TTL with BJTs, a floating input is usually pulled up to V+
> inside the chip, but this is not guaranteed so your inputs should never
> be floating (always tie unused inputs to either V- or V+).
Uh... OK. I never did that before - but hey, maybe that's why half my
circuits didn't work?
Damnit, I thought digital electronics was just about on or off. :-/
> *Outputting*
> a floating signal is just a disaster is normal logic (there is nothing
> to stop some very small amount of interference driving it high), and
> usually only used where you need to have more than one output connected
> to the same line (eg the data bus inside your PC - each connection to it
> should be able to output low, high, or not-connected).
You speak of "3-valued logic" with it's "Hi-Z" mode?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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On Mon, 18 Aug 2008 13:18:36 +0100, Invisible <voi### [at] devnull> wrote:
>Stephen wrote:
>
>> TTL is slower and uses more power.
>> I once built a clock out of TTL, in the mid 70's it used IIRC 50 amps at 5 Volts
>> Vcc. A couple of years later a CMOS clock ran from a PP3 battery
>
>50 amps? Shouldn't that tend to cause wires to melt and so forth?
That was the total current supplied from the PS but there were lots of cards
taking significantly less current. IIRC TTL uses about 50 m.a. per chip. And the
wires won't melt if they are rated for it.
>Hey, isn't CMOS that stuff that breaks if you get static on it?
Yes, at one time I worked for Motorola and had unlimited supply of the stuff :)
--
Regards
Stephen
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>> 50 amps? Shouldn't that tend to cause wires to melt and so forth?
>
> That was the total current supplied from the PS but there were lots of cards
> taking significantly less current. IIRC TTL uses about 50 m.a. per chip. And the
> wires won't melt if they are rated for it.
Well, 30A wire is so thick that you have to bend it with pliars and a
hammer. I'd hate to think what 50A wire is like! o_O
>> Hey, isn't CMOS that stuff that breaks if you get static on it?
>
> Yes, at one time I worked for Motorola and had unlimited supply of the stuff :)
OK. So I think I'm building my device using TTL, just so I don't *break*
the thing before it's finished. :-S
(You know, Maplin used to sell practically the entire 7400 range. Now it
seems they only sell 6 models. Also, the 7400 used to be 21.62p. It's
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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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.
> 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.
> 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.
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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?
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