cheap and simple way to measure temperature

[Heckler]

hey Mack,

But if VDD is a 3 volt lithium coin cell whose voltage decreases over time, will that make the temperature also become less accurate over time?

Although, even if that is the case, that may be an acceptable amount of drift for this type of project.

Thanks I'll have to break out the breadboard (DANG!... Now the fun starts)

Still open to suggestions, though.
Price is really the main factor for my needs.

Dwight

[mackrackit]

I wonder how long a project like yours willrun with a coin battery?
Will the coin also be running the motor?

[Heckler]

I wonder how long a project like yours willrun with a coin battery?
Will the coin also be running the motor?

The Coin Cell only runs the PIC and the 7 LED's.

The project is designed to simply be waived back and forth in the air to view the POV message. Or better yet most people will attach it to a paint stir-stick (a thin 1" wide by 12" long woden stick) with black tape or a rubber band, then with a 16d nail poked through the stir stick (or some orther sort of handle attached to one end of the stick) twril or spin the thing around to view the message. It actually works quite well. The kids can use their imagination and come up with other ways to spin the thing around to properly display the POV image (I lump myself in that KID category any time I am working with electronics, at least I always seem to have fun melting solder.)

Dwight

[ardhuru]

When I made my POV propeller clock I was also tempted to include temperature display, besides the time and the calendar. What gave me second thoughts was the fact that the PCB would be spinning all the time, and therefore the temperature being displayed was unlikely to be exactly the ambient.

Are you sure your POV stick, while it is being waved, would also not influence the sensor's readings?

Just a thought...

Anand

[mackrackit]

Hand motored... That sounds interesting. They could even put them on the spokes of their bikes.

The LM34 may not be the best option then.

[El_AMPo]

When I made my POV propeller clock I was also tempted to include temperature display, besides the time and the calendar. What gave me second thoughts was the fact that the PCB would be spinning all the time, and therefore the temperature being displayed was unlikely to be exactly the ambient.

Are you sure your POV stick, while it is being waved, would also not influence the sensor's readings?

Just a thought...

Anand

Check how old fashion wet bulb hygrometers work,
http://www.agri-shop.co.uk/whirling-hygrometer-37-p.asp
Spinning all around but still the best readings, so no problem with the winding, probably a bad idea because of line noise if you weren't using batteries, but is not the case.

If you want a really CHEAP thermometer with decent accuracy use a diode as a sensor.
Here is the schematic:


Still working for me at a 0.5ºC resolution, but needs a two point slope calibration, some chip math and a pic with ADC.

Maybe the 10bit ADC will give you a resolution of 2-3ºC, maybe less with oversampling with just the 4k7 resistor and the diode directly to the adc.
Anyone for the test of oversampling?
http://www.darreltaylor.com/DT_Analog/

[fixitjs]

Be careful not to confuse ambient temperature with wind chill. objects will not cool to a lower temperature then the ambient temp, but will cool at a rate of the wind chill. thus, swinging the isplay stick will give you an accurate temp reading as any temperature increase caused by holding it will be released by the air flow accrossed the stick but not lower then the ambient temperature. hope this is helpful.

[mtripoli]

Have a look at the LM94022. Price is $1.27 from Digikey you can get the data sheet there as well (I had a link but Digikey uses scripts and the link comes out bad). It has a couple of options for gain set through pins. The biggest downside to this part is the package; not user friendly for hand soldering.

IIRC the LM34 is a little weird that it requires a negative bias to give voltages below 0 or something, and it only operates down to 5V.

Good luck.