> Yan Seiner wrote:
>> Does anyone have any suggestions for a cheap thermocouple?
>>
>> I am looking for something that can be put into a small animal
>> environment (cage or tank) so it has to be low voltage and visually
>> unobtrusive; ideally something like the stick-on strain gauges that I
>> can run DC voltage through, and stick on to some out-of-sight portion
>> of the tank.
>>
>> My plan is to run it into the A/D on one of these boards, and control
>> heaters based on the input.
>>
>> I'm coming up dry with Google; I don't need/want a large, industrial
>> unit. I need something a homeowner/pet owner wouldn't notice.
>>
>> --Yan
Hi Yan,
So you've had a few suggestions. Made any decisions yet?
Here's a few more comments to help:
1. 1-Wire temperature sensor
* DS18B20 in TO-92 (or other packages)
* requires a bit-banged 1-Wire interface
(which is pretty simple)
* I've got VHDL that automates the interface
(you're welcome to it)
2. VBE band-gap references
* either fully digital versions, eg. the LMxxx series
from National Semiconductor, or the ADMxxx series
from Analog devices. These chips generate 10uA and
100uA current sources and drive them into a
diode-connected transistor, measure the voltage,
and convert the results to a digitizer temperature
reading. I use the ADM1031 to measure FPGA diodes.
Maxim has a multi-channel ADC with a built in
diode-conditioning circuit.
* analog versions, eg. use a 1mA current source
and measure the voltage on the diode-connected
transistor. For example, use an LM4041 band-gap
reference
http://cache.national.com/ds/LM/LM4041.pdf
and an op-amp to create the 1mA current source,
and another op-amp to generate offset and gain.
The signal conditioning circuit can be on your
ADC board, while the sensor is just a TO-92
transistor. I have a circuit to do this for
a diode in a 1GHz digitizer and for measuring
a thermal resistor in a PowerPC.
3. Commercial temperature probe.
* a Radio Shack sensor was suggested by a previous
poster
The sensor to choose depends, in part, on whether you
are using one or more of these sensors. The 1-Wire
devices are annoying in that respect; its hard
to identify the physical device location from the
chip alone. The I2C VBE devices are nicer in that
respect, and if your micro already has I2C, then
its a lot simpler to interface to.
As far as sensor size goes; they're both the same,
i.e., a 1-Wire in TO-92 or a diode-connected transitor
in TO-92.
So it pretty much comes down to how much work you
need to do at the board-end of things.
Cheers,
Dave
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/
|