Recomendations for Temperature Sensor for Custom Thermostat?

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I'd like to prototype a custom thermostat with several novel features and
I'd appreciate recommendations for a temperature sensor -- I'll probably use
two, one for the inside temperature and one for outside to use in predicting
heating/cooling needs.

TIA
    Norm



Re: Recomendations for Temperature Sensor for Custom Thermostat?

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I'd use thermistors with a Cygnal 8051 w/ ADCs from www.cygnal.com or an
MSP430 w/ ADCs from www.ti.com.

--
- Mark ->
--

Re: Recomendations for Temperature Sensor for Custom Thermostat?

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The present "cute game" for temperature sensors is to use a diode or
diode-connected transistor and drive it with a square-wave of current
with minimum value 1*Io and maximum value 10*Io (your choice of Io);
thus the square-wave voltage (AC-term) that results is kT/q*ln(10) (T
on K)

Thus you don't have to calibrate the device ;-)

                                        ...Jim Thompson
--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Re: Recomendations for Temperature Sensor for Custom Thermostat?
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I am impressed.



Re: Recomendations for Temperature Sensor for Custom Thermostat?

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You're not alone.  I like "cute" in electronics.

Re: Recomendations for Temperature Sensor for Custom Thermostat?
I like the Analog Devices AD590. It is a current device so voltage
drop when used remotely is not a problem. Go to their website for info
and check out application note AN-273. Incidently, the resistor
values in the app note for the voltage divider appear to be wrong.

Doug

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use
predicting



Re: Recomendations for Temperature Sensor for Custom Thermostat?

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use
predicting

I've used planar epitaxial diodes as temperature sensors with good results.
They have a nearly linear voltage vs. temperature coefficient over a
reasonably wide temperature range. The only problem with them is you would
need some amplification to get the voltage up to a useable range and they
should be driven by a constant current source.
http://www.fairchildsemi.com/ds/1N/1N914A.pdf



Re: Recomendations for Temperature Sensor for Custom Thermostat?
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While I like the method that Jim mentioned for more sloppy no-cal
temperature control, I'd hesitate to recommend it for HVAC systems
because it's not quite accurate enough. It also has a fairly low
output voltage of a couple of hundred uV/K which requires a bunch of
compenents unless you're designing an ASIC.
Jim:- one manufacturer claims *automatic* compensation for rb (?) the
base resistance, which as I understand it is the most important error
term. Do you know how they are doing that?

Instead, I suggest using a precision 1% thermistor. It will be much
more accurate than most other types of cheap sensors at room
temperature (which is pretty much the only temperature that counts in
the HVAC field). It's also cheap and low system component count if you
ever decide to make a zillion of them. It requires no absolute voltage
reference, only a reference resistor.

P.S. This is the type of sensor you'll find in virtually every piece
of consumer electronics with a temperature display, from
indoor/outdoor thermometers to fever thermometers. The technology was
refined by the Japanese to create all those markets.

Best regards,
Spehro Pefhany

Re: Recomendations for Temperature Sensor for Custom Thermostat?
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You might want to consider the Maxim (Dallas) 1-Wire temperature
sensor, which can simplify wiring of multiple remote sensors:

<http://para.maxim-ic.com/compare.asp?Fam=Temp_Sens&Tree=1Wire&HP=1-Wire.cfm&ln=&SORD44%8&FT_44878%72&FT_44880%87&ITEMLIST11%9437,119438,119439,119440,119441,119442,119443,119444

Re: Recomendations for Temperature Sensor for Custom Thermostat?
I've used the National LM34 series for about 20 years(ugh, time flies) in
hundreds of remote energy control systems.
Have never had a failure yet.
Those Dallas 1-wire parts look nice,providing you have a micro( my system is
discete 4000 series CMOS)
Be aware of RF,EMI,etc as possible 'noise' sources.
hth
jay



Re: Recomendations for Temperature Sensor for Custom Thermostat?



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Maxim has some nice new chips (MAX6642 and MAX6665) that can use an
external diode as the sensor. They have an SPI interface.

Leon
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Leon Heller, G1HSM Tel: +44 1424 423947
Email: aqzf13 at dsl dot pipex dot com
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