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temp controller

K

Krash

Jan 1, 1970
0
I need schematic of a controller that will turn a light bulb on [regular
120v] at a certain temp, and when the temp rises to a set level, turns the
light back off, any ideas?
 
J

Jerry Girard

Jan 1, 1970
0
Use a thermistor into comparator and the comparator switching a TRIAC to
control the light. Use the comparator hysteresis to control the on and off
cycle rate.
 
M

Mac

Jan 1, 1970
0
I need schematic of a controller that will turn a light bulb on [regular
120v] at a certain temp, and when the temp rises to a set level, turns the
light back off, any ideas?

I doubt anyone will draw a complete schematic for you. It's a lot of work.
But what you need is a temperature sensor, say a temperature to voltage
converter. This could be connected to a comparator with a reference
voltage corresponding to your temperature set point. Be sure to put in
some hysteresis so the bulb doesn't just flicker on and off.

Then the comparator output would have to actuate the light bulb. This
means your low-voltage DC circuit would have to somehow open and close the
120 V circuit containing your lighbulb. A relay might serve this purpose.
There are probably solid state devices, for this, too.

The sensor/comparator part seems pretty straighforward to me. However, I
don't have any experience switching house voltage from a DC circuit. I'm
sure others here have done this, though.

Mac
 
B

Ban

Jan 1, 1970
0
Jerry Girard wrote:
|| See attached schematic link:
||
|| http://www.lillyct.com/temp.gif
||
|| Add your own +5V power supply. The values suggested for the
|| hysteresis feedback should get you started. Enjoy.

It should be mentioned that the shown circuit is very difficult to
calibrate, because the two pots are interdependent, much better would be to
use the second comparator for the lower threshold and the other to switch
off. No additional components needed. :)
VCC ___2k2
+-----------------|___|-+
| ___ |
.-. +-|___|-+
| | | 2M2 |
| | | |\ |
'-' +-|+\ |
| | |A >--+ LM393
+---------+---+-)-|-/ | |\
| | | | |/ | +--|-\
.-/> | | | LM393 | | |B >-to MOC3010
|/| --- +-)-------)---|--|+/
/ |Therm. --- | | | |/
</'-' |0u1 | | |
| | | | |
=== === | | |
GND GND | | |
| | |
| | |
VCC | | |
| | | |
.-. | | |
| | 10k | | |
| | | | |
'-' | | |
| | | |
.-. low threshold| .-. |
| |<-------------+ | |<-+
| | 10k 10k | |high
'-' '-'threshold
| |
=== ===
GND GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Another difficulty is that the specialized optocoupler MOC3010 is not easily
available.
 
W

Walter Harley

Jan 1, 1970
0
Krash said:
I need schematic of a controller that will turn a light bulb on [regular
120v] at a certain temp, and when the temp rises to a set level, turns the
light back off, any ideas?

It depends on how precisely you're trying to control, and what you're trying
to control. You could use a thermostat; they're very cheap in hardware
stores. If you need precise control, or the system you're trying to heat
has a lot of thermal lag, you may need a device called a "PID controller" -
google for that to learn more.

I hacked my espresso machine to use a PID controller rather than a
thermostat :)
 
H

hamilton

Jan 1, 1970
0
Walter said:
I hacked my espresso machine to use a PID controller rather than a
thermostat :)

I like espresso.

Did the better temp control of the water help the brewing process ??
 
W

Walter Harley

Jan 1, 1970
0
hamilton said:
I like espresso.

Did the better temp control of the water help the brewing process ??

Yes, quite a bit. For two reasons: first, the temp is more reliable from
shot to shot; second, I can adjust it for different kinds of beans. (Darker
roasted beans like the water a little less hot.)

The machine is a Gaggia Classic, which is already a good machine with a
powerful heater and a lot of thermal mass. But the PID has really made a
surprising amount of difference. It used to be that one in three shots was
really good; now I can consistently get the same quality.

There's often discussion of this on alt.coffee, if you want to learn more.
 
H

hamilton

Jan 1, 1970
0
Walter said:
Yes, quite a bit. For two reasons: first, the temp is more reliable from
shot to shot; second, I can adjust it for different kinds of beans. (Darker
roasted beans like the water a little less hot.)

The machine is a Gaggia Classic, which is already a good machine with a
powerful heater and a lot of thermal mass. But the PID has really made a
surprising amount of difference. It used to be that one in three shots was
really good; now I can consistently get the same quality.

There's often discussion of this on alt.coffee, if you want to learn more.

Walter,

Would you please post more information about the PID controller.

Did you build / program the controller yourself, or
did you buy an off-the-shelf controller ?

Any information about the controller itself would be fun.

Thanks

hamilton AT dimensional DOT com
 
W

Walter Harley

Jan 1, 1970
0
hamilton said:
Would you please post more information about the PID controller.

Did you build / program the controller yourself, or
did you buy an off-the-shelf controller ?

Any information about the controller itself would be fun.

Well, as I said, the best place to learn more is on alt.coffee (or on
http://www.coffeegeek.com). Quite a few of the folks there have done this.

But in brief: I used an off-the-shelf PID controller and a solid-state
relay. The controller cost about $90, second-hand but unused; it's a little
thing, about 1"x2.5". These live in a steel chassis that sits underneath
the espresso machine. Within the espresso machine, the thermostat is
disconnected and the wires instead run to a connector on the back of the
espresso machine (and thence to the controller chassis), and a K-type
thermocouple is also run from the controller into the espresso machine and
attached to the boiler.

The PID controller has an auto-tune mode, that takes about half an hour to
run. It heats up and cools down the boiler a few times and watches the time
constants.

I'll post a picture and a schematic to alt.binaries.schematics.electronic
for your entertainment.
 
H

hamilton

Jan 1, 1970
0
Walter said:
Well, as I said, the best place to learn more is on alt.coffee (or on
http://www.coffeegeek.com). Quite a few of the folks there have done this.
I'll post a picture and a schematic to alt.binaries.schematics.electronic
for your entertainment.

Thanks for that.

I am looking at this as overkill.

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).

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.

Have to admit, the mods look great.

We all have our hobbies. :)

hamilton
 
W

Walter Harley

Jan 1, 1970
0
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
 
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