 |
|
|
|
|
|
| |
| |
|
|
|
|
| |
| |
|
|
What *is* the difference between a BJT and a FET?
Are they different designs for doing the same thing, or do they actually
"do" something different?
How do you use them anyway?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Invisible wrote:
> What *is* the difference between a BJT and a FET?
I think I can describe the difference (a little) with an analogy.
Think of a BJT like two pools of water, with a low spot between, hoses
connected. To make the water flow, you pump enough water into the low
spot that the water from the hoses can flow across. Of course, this
washes away the water you pumped in, so you have to pump in more.
A FET is like a balloon wrapped around a hose. To make the water stop
running, you pump water into the balloon, which squeezes off the hose.
But since it's in the balloon, it really doesn't leak as such, so the
efficiency is much better.
Of course, these are *way* simplified descriptions. If you really care
how the semiconductors work at the quantum level, I can go into that,
but it didn't sound like the kind of question you were asking.
Look at the wiki pages for each. In the BJT, the current flows from the
blue, thru the green, and into the other blue. That's the "bipolar
junctions", the two boundaries.
In the FET, there's the "gate" and the "oxide" that keeps the gate from
actually conducting the electricity you put on it. But when you charge
up the gate, the "static electricity" pulls/pushes away the charges that
actually conduct between the two "N" pads there. So, FETs are used in
things like wrist watches, which are expected to run for a year on a
tiny little battery, because they work on voltage rather than current,
and batteries are better at supplying voltage than current.
> Are they different designs for doing the same thing, or do they actually
> "do" something different?
The do "the same thing" in different ways. The BJT is less efficient but
it can handle much larger currents (i.e., the "hose" can be bigger
because you don't need to wrap a balloon around it).
> How do you use them anyway?
They're basically amplifiers of electricity. If you want to make binary
circuits, you over-drive them so they're either completely off or
completely on.
--
Darren New / San Diego, CA, USA (PST)
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Darren New wrote:
>> Are they different designs for doing the same thing, or do they
>> actually "do" something different?
>
> The do "the same thing" in different ways.
OK. So you'd wire them both up in essentially the same way?
Is there any major overall difference in operating characteristics? (I
seem to recall that whichever one you pick there's about 50,000,000
models to choose from anyway!)
>> How do you use them anyway?
>
> They're basically amplifiers of electricity. If you want to make binary
> circuits, you over-drive them so they're either completely off or
> completely on.
So why is it that (say) a simple NAND gate involves 8 transistors, 3
diodes and 25 resistors? That doesn't make any sense to me... Logically
it looks like any possible 2-input gate should require 1 or 2 switches
and nothing else.
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Orchid XP v8 wrote:
> OK. So you'd wire them both up in essentially the same way?
You're getting a bit past my expertise, but yes, physically there's
three connections with the same functions on each. Electrically, of
course, there's different voltages, switching times, etc. It's like
asking if you drive a camper essentially the same way as you drive a VW bug.
Note that you also wire up vacuum tube triods in "essentially the same
way", so I'm not sure how helpful that answer is. ;-)
> Is there any major overall difference in operating characteristics?
Well, yes. I thought I'd been clear on that. They take different
voltages and handle different currents and so on.
> So why is it that (say) a simple NAND gate involves 8 transistors, 3
> diodes and 25 resistors? That doesn't make any sense to me... Logically
> it looks like any possible 2-input gate should require 1 or 2 switches
> and nothing else.
To make a switch, you have to either switch to + or to -, so that's at
least two switches right there. I.e., you need two transistors, one to
amplify the + voltage, and one to amplify the - voltage, using CMOS FET,
just to make a NOT gate. Depending how you do it, it may take diodes
and resistors and such.
--
Darren New / San Diego, CA, USA (PST)
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> OK. So you'd wire them both up in essentially the same way?
Essentially, yes, but you need to bear in mind the differences between the
two when designing your circuit. The main difference is that a FET is
controlled by input voltage, and the BJT by input current. So in most
designs with BJTs you'll see some resistors dotted around to control the
current.
> Is there any major overall difference in operating characteristics? (I
> seem to recall that whichever one you pick there's about 50,000,000 models
> to choose from anyway!)
Good point about FET is that they have almost infinite input impedance,
which is often useful for low-power operation or when measuring very low
powered signals. Good point about BJT is that the output resistance is
higher, so good for driving higher powered devices rather than pure digital
signals.
> So why is it that (say) a simple NAND gate involves 8 transistors, 3
> diodes and 25 resistors? That doesn't make any sense to me... Logically it
> looks like any possible 2-input gate should require 1 or 2 switches and
> nothing else.
A NAND gate needs 4 FETS and no resistors:
http://en.wikipedia.org/wiki/Image:CMOS_NAND.svg
Inside an IC, resistors are HUGE compared to FETs, there is no way you could
make a modern CPU if you needed to include resistors for each gate.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> OK. So you'd wire them both up in essentially the same way?
>
> Essentially, yes, but you need to bear in mind the differences between
> the two when designing your circuit. The main difference is that a FET
> is controlled by input voltage, and the BJT by input current. So in
> most designs with BJTs you'll see some resistors dotted around to
> control the current.
See, in theory the way a transistor works is supposed to be simple.
However, every transistor circuit I've ever looked at seems so damned
complicated...
> Good point about FET is that they have almost infinite input impedance,
> which is often useful for low-power operation or when measuring very low
> powered signals. Good point about BJT is that the output resistance is
> higher, so good for driving higher powered devices rather than pure
> digital signals.
...and this is why I like to stick to logic circuits. You don't have to
worry about obscure concepts like impedance or capacitance. (I mean,
unless you're designing "high performance" circuits anyway.)
>> So why is it that (say) a simple NAND gate involves 8 transistors, 3
>> diodes and 25 resistors? That doesn't make any sense to me...
>> Logically it looks like any possible 2-input gate should require 1 or
>> 2 switches and nothing else.
>
> A NAND gate needs 4 FETS and no resistors:
>
> http://en.wikipedia.org/wiki/Image:CMOS_NAND.svg
>
> Inside an IC, resistors are HUGE compared to FETs, there is no way you
> could make a modern CPU if you needed to include resistors for each gate.
Even so, you can make a NAND gate out of just 2 electromechanical
relays. Why does it require twice that number when you use transistors?
(Additionally, I can't make any sense out of that diagram. The wiring
seems to have no reason or rhyme to it.)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> See, in theory the way a transistor works is supposed to be simple.
> However, every transistor circuit I've ever looked at seems so damned
> complicated...
You mean something like this - a simple amplifier circuit?
http://www.cjseymour.plus.com/layin/BJTAMP.jpg
The reason it looks complicated is because you are using a
current-amplifying device (the BJT) to amplify voltage.
The two resistors on the left are to bias the input voltage to somewhere in
the middle of the operating range of the transistor. Otherwise you cannot
amplify negative input voltages (quite common in audio signals...).
The capacitor on the left allows the input voltage to be added to the bias
voltage.
Resistor R3 causes the amount of current flowing out of the emitter to be
(almost) proportional to the input (base) voltage. Capacitor C2 helps to
boost the gain by allowing AC signals to see a lower resistance to ground,
but still keeping the DC operating point.
Resistor R4 generates the output voltage proportional to the amplified
current flowing through the collector/emitter. Capacitor C3 removes any DC
component of the signal.
Note that the circuit inverts as well as amplifying...
> ...and this is why I like to stick to logic circuits. You don't have to
> worry about obscure concepts like impedance or capacitance. (I mean,
> unless you're designing "high performance" circuits anyway.)
Even with logic circuits, you cannot connect a single output to 5000 inputs,
there is always a limit due to internal resistances. At some point your
circuit is going to fail, and for some technologies the number is much lower
than 5000.
> Even so, you can make a NAND gate out of just 2 electromechanical relays.
How?
> Why does it require twice that number when you use transistors?
> (Additionally, I can't make any sense out of that diagram. The wiring
> seems to have no reason or rhyme to it.)
Out is either connected to Vss (low) or Vdd (high) depending on the inputs A
and B. If A or B or both are low, then Out gets connected to Vdd because
one (or both) of the top FETs will start conducting. Only if both A and B
are high will there be a link between Out and Vss.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> See, in theory the way a transistor works is supposed to be simple.
>> However, every transistor circuit I've ever looked at seems so damned
>> complicated...
>
> You mean something like this - a simple amplifier circuit?
>
> http://www.cjseymour.plus.com/layin/BJTAMP.jpg
Yeah, pretty much.
The books say "a transistor is an amplifier" - and then should you a
*working* amplifier which actually consists of almost a dozen
components, of which the transistor is only one.
> The reason it looks complicated is because you are using a
> current-amplifying device (the BJT) to amplify voltage.
Uh... does it matter? I mean, the two are inherantly linked anyway...
>> ...and this is why I like to stick to logic circuits. You don't have
>> to worry about obscure concepts like impedance or capacitance. (I
>> mean, unless you're designing "high performance" circuits anyway.)
>
> Even with logic circuits, you cannot connect a single output to 5000
> inputs, there is always a limit due to internal resistances. At some
> point your circuit is going to fail, and for some technologies the
> number is much lower than 5000.
Yeah, but I'm never likely to build anything that even *contains* 5,000
components in total, am I? ;-)
>> Even so, you can make a NAND gate out of just 2 electromechanical relays.
>
> How?
Let's assume that a positive potential represents logic high, and a zero
potential represents logic low. Take a pair of relays connected up so
that by default the circuit is closed, and energising the magnet opens
the circuit. (This is easy to arrange with 3-pin switch type relays.)
Connect the relays in parallel between the positive rail and the signal
output terminal. Connect each input to one side of one magnet coil, and
connect the other sides to the negative rail. Done.
>> Why does it require twice that number when you use transistors?
>> (Additionally, I can't make any sense out of that diagram. The wiring
>> seems to have no reason or rhyme to it.)
>
> Out is either connected to Vss (low) or Vdd (high) depending on the
> inputs A and B. If A or B or both are low, then Out gets connected to
> Vdd because one (or both) of the top FETs will start conducting. Only
> if both A and B are high will there be a link between Out and Vss.
It probably doesn't help that I'm not understanding the symbols in the
diagram, but OK...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> The reason it looks complicated is because you are using a
>> current-amplifying device (the BJT) to amplify voltage.
>
> Uh... does it matter?
Well yeh, that's why the resistors are needed. Generally you want to
amplify voltages, not currents.
> Let's assume that a positive potential represents logic high, and a zero
> potential represents logic low. Take a pair of relays connected up so that
> by default the circuit is closed, and energising the magnet opens the
> circuit. (This is easy to arrange with 3-pin switch type relays.) Connect
> the relays in parallel between the positive rail and the signal output
> terminal. Connect each input to one side of one magnet coil, and connect
> the other sides to the negative rail. Done.
I don't understand what is connected to the negative rail?
Don't forget that the output must be connected to either the negative or
positive rail (and not both!) under all input conditions. It sounds to me
like in your circuit, the output will just be floating (ie not connected to
anything) when you charge both relays.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>>> The reason it looks complicated is because you are using a
>>> current-amplifying device (the BJT) to amplify voltage.
>>
>> Uh... does it matter?
>
> Well yeh, that's why the resistors are needed. Generally you want to
> amplify voltages, not currents.
...because you don't want to actually push too many electrons around and
warm up the wiring?
>> Let's assume that a positive potential represents logic high, and a
>> zero potential represents logic low. Take a pair of relays connected
>> up so that by default the circuit is closed, and energising the magnet
>> opens the circuit. (This is easy to arrange with 3-pin switch type
>> relays.) Connect the relays in parallel between the positive rail and
>> the signal output terminal. Connect each input to one side of one
>> magnet coil, and connect the other sides to the negative rail. Done.
>
> I don't understand what is connected to the negative rail?
>
> Don't forget that the output must be connected to either the negative or
> positive rail (and not both!) under all input conditions. It sounds to
> me like in your circuit, the output will just be floating (ie not
> connected to anything) when you charge both relays.
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. (After all, a digital
circuit is just a circuit that has two possible states. It doesn't
matter especially what those states are, so long as everybody agrees...)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
On Mon, 18 Aug 2008 10:09:58 +0100, Invisible <voi### [at] dev null> wrote:
>Even so, you can make a NAND gate out of just 2 electromechanical
>relays.
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.
--
Regards
Stephen
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
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*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
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*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
On Mon, 18 Aug 2008 12:45:13 +0100, Invisible <voi### [at] devnull> 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
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> 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).
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
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*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> 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*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
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
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> 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
now something like £1.20. How times have changed...)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> 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.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> 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?
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> 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*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> 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".
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> 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*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> 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? ;-)
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> 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*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> "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.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
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!
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
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] ... )
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> 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
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> 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
Cool videos, we did that as part of our Engineering course, nice touch with
the water on the pendulum!
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
|
|
