I agree. I've done this before. You design in a little hysteresis and
you're all
set. Just turn the heater on a couple degrees below where you turn it off.
You have plenty of time. You could use a relay, the contacts going to
the heater.
You could use a DIO pin driving the base of a transistor to operate the
relay coil.
You would of course need to have a back EMF diode across the coil as well.
Larry
Gonzalo A. de la Vega wrote:
> --- In <ts-7000%40yahoogroups.com>,
> "Yan Seiner" <> wrote:
> >
> > --- In <ts-7000%40yahoogroups.com>,
> Joel Winarske <joelw@> wrote:
> > >
> > >
> > > > I'm kicking around the idea of controlling an ordinary 120 VAC
> > > > incandescent light (actually a 150W heater).
> > > >
> > > > I'd like to control the heater based on the temperature of the
> surface
> > > > beneath it. I need to control it to approximately 105 deg F (more or
> > > > less; great accuracy is not needed here.)
> > > >
> > > > I've found some basic PIC circuits on the web but I wonder if anyone
> > > > here has any suggestions, both for the temp probe and for the heater
> > > > control.
> > > >
> > > > As this will most likely be a one-off, an inexpensive commercial
> > > > solution would be fine.
> > > >
> > >
> > >
> > > You would need:
> > > 1. Zero Crossing input
> > > 2. DC Power circuit
> > > 3. PWM / Triac Control
> > > 4. Load current protect circuit
> > > 5. temp measurement - A/D
> > > 6. Control interface - RS485/CAN/RS232
> > >
> > > The NXP LPC2xxx is a good fit for this.
> > >
> > > How many channels do you need?
> > > How far from the controlling device do dimmer channels need to be
> > located?
> > >
> >
> > Sorry, I should have been more detailed....
> >
> > I want to run the temp probe into the A/D inputs on a TS7xxx board,
> > and then have the board control the heater.
> >
> > The reason for this is that I also want the ability to set up a webcam
> > and multiple control channels, and I want web-based programmability.
> >
> > So I'm really looking for a 120VAC dimmer that can be run by a TS7200.
> > All I've been able to find are PIC based designs, which I could
> > probably adapt, but I am not a hardware person...
> >
> > --Yan
> >
>
> Depending on the thermal conductivity and thermal capacity of what you
> are controlling, and the precision you need, may only need a
> thyristor: usually the time constants of temperature controlled
> systems is quiet large (like tens of seconds), so just turning the
> heater on and off is enough. If this is the case you won't need a PWM
> output either, just binary.
> Note that by saying a thysritor I mean any on-off device: triac, or
> relay too. A thyristor is rectifying, so you'll get at most 1/2 the
> power unless you use two of them.
>
> Gonzalo
>
>
------------------------ Yahoo! Groups Sponsor --------------------~-->
Great things are happening at Yahoo! Groups. See the new email design.
http://us.click.yahoo.com/lOt0.A/hOaOAA/yQLSAA/CFFolB/TM
--------------------------------------------------------------------~->
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/ts-7000/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/ts-7000/join
(Yahoo! ID required)
<*> To change settings via email:
<*> To unsubscribe from this group, send an email to:
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
|