>> 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