On 1/29/2015 11:37 PM, Richard wrote:
On 1/29/2015 11:08 PM, gary wrote:
Looking for a thermostat that will allow the temp to be set up or
down temporarily, and after an interval, will reset to the
pre-programmed temp.

Also, to enable/disable the whole house fan, then also, after an
interval, reset to programmed value.

Not finding what I need on the internet, probably because I don't know
what it's called or described.

thanks

gary


Would be a reasonable DIY project for a microcontroller.

BASIC Stamp, Propeller, Pic...

One thing you don't want to do is break your HVAC system.
There are timers and lockouts and etc. in there to keep the
system from hurting itself.

One way to get started is to use a heater coupled to the thermostat
temperature sensor. Resistor or light bulb stuffed inside the
housing near the sensor.

You set the thermostat for the highest temperature you want.
To get lower, you apply some heat to the sensor.
Measure the actual temperature with your microcontroller
and just drive the resistor when you want the temperature to go lower.

That is minimally invasive and probably won't hurt your HVAC system
no matter how often your program crashes ;-)
You can even do warmer/colder with a Peltier device as the "heater".

My favorite platform for this kind of thing is the Palm 3C PDA.
Dirt cheap.
You can program it in BASIC. Full GUI interface.
I/O is an issue. You have one easily available input and one output
at the serial port interface. I've used serial commands to drive a PIC
processor that does the actual control interface when I needed more I/O.
And if you step up to a more recent Palm, you can use bluetooth
for wireless access. You can also use the IR interface as a serial
communication port.

The link is a prototype of a system that monitors a flapper on the
heater vent, subtracts the delays to calculate the ON-time of the
gas to the furnace and logs and plots that.

http://i.imgur.com/vsaPixW.jpg

You could certainly do this with a dedicated microcontroller, but this
is dead simple.

When I get up in the morning and turn on my PC, I can watch the
gas furnace throttle down due to the extra heat from the computer.
Was way cool for about a week. It did alert me when the furnace
started acting up and the graph differed from the norm.

Beware this stuff is addictive. You may soon find yourself building
all manner of gadgets that you won't ever use. Guess that's the
definition of "hobby".