hamilton said:
I am looking at this as overkill.
Arguably, owning an espresso machine at all is overkill... anything beyond
that, such as modifying it for better coffee, is surely overkill. As you
say, we all have our hobbies
A simple temp controller was posted here ( or comp.embedded ).
The thermal mass of the water means that the boiling will take a while,
keeping the temp at a set point temp ( within 1 degree F) should be easy
even with an analog temp controller (as posted).
There's a substantial time lag between when you start dumping energy into
the boiler, and when the temperature sensor detects a change. That time lag
is your enemy, in terms of process control. I think you'll find that a
naive system has considerable overshoot, and takes a long time to stabilize
after pulling a shot, if it ever stabilizes at all. More likely, it'll
constantly oscillate (at 0.05Hz or so) over a range of several degrees.
If the problem of accurately controlling water temperature in a boiler was
really all that easy, PID controllers wouldn't exist... it's one of the main
things they're used for, I think.
I am looking at getting an espresso machine after xmas. (for myself)
I will put together some low cost temp control designs myself.
I found a web site with PID controller info. This looks great.
<
http://www.quiknet.com/~frcn/Coffee/Coffee63.html>
But adding $200 to an already $350 unit seems a little crazy.
That's a good page, as are the other ones it references.
The question is not whether adding $200 to a $350 unit is crazy, the
question is whether having a $550 espresso machine is crazy. Arguably it
is. Me, I keep thinking about moving up from the Gaggia + PID combo to an
$1100 Isomac. So yes, I'm crazy
-w