Xbee Wireless Temperature Sensor

[adafruit]

thats right! you should calculate it that way. make sure vref is tied to 3V (to set the 'top' voltage level) you're very close

[Pelphry17]

Hey Everybody...."Norm!" Sorry showing my age..

Anyway I'm having trouble with my wireless temp. monitor using the Xbee and TMP36. I'm using a modified code from theTweet-A-Watt (thanks again) and Adafruit's xbee adapter. I have the TMP36 hooked up with the analog out to AD0 on the adapter, GND to GND, and V+ pin to VCC and VREF (3.3v) on the adapter. I am getting readings just fine every two seconds, however they fluctuate as much as 10 degrees F or more on each cycle.

Could this be an interference problem or even power supply. My 3.3V on VREF holds very solid while transmitting. Stumped and could use some expert advise. Thanks.

Code: Select all

mVolts = xb.analog_samples[0][0]  # Report the millivolts from the TMP36
voltage = mVolts * 3.3 / 1024
tempC = (voltage - .5) * 100             
tempF = math.floor(tempC * 9 / 5 + 32)         


[adafruit]

whats the 10bit value returned? does that vary?

[Pelphry17]

Yes, the "mVolts" is changing from around 85 to over 130. The actual temp outside is 19F.

[adafruit]

ok, use a multimeter to measure the voltage from the TMP36 as it goes into the ADC

[Pelphry17]

Ok. I will get that measurement tonight. I was thinking...I am using this step up circuit (single cell) and it says it has a ripple of 150mV.
http://www.bodhilabs.com/info.html
Plus the spec sheet for the TMP36 mentions using a .1uF bypass capacitor on the input. I do not have that. Could either of these be part of problem?

[adafruit]

150mv is -a lot- of ripple. you really need a LDO or just batteries. really!

[FlyingSaucrDude]

Does anyone still have the pictures showing the wiring stashed somewhere? Flickr doesn't seem to have them anymore...

[zachschi]

Hello, I second that, any images still hosted out there? I would be willing to host them also. Thanks.

[zard]

Sorry for necromancing, but TMP36 lists output voltage in range 100-2000mV - wouldn't that be a problem for the Xbee's input pins? I recall they have an upper limit of 1.2V

[adafruit_support_rick]

I haven't looked myself, but according to the third and fourth posts in this thread, the voltage limit on analog in is 3.3V

[Lawndart]

Here is my prototype. TMP36 attached to an Xbee S1 on an XBee Explorer USB board connected to an iPhone USB charger via an adapter.
Working wonderfully in proto-stage.


Planning on using this as the remote sensor for my ThermoNixie. My plan is to mate the remote Xbee with one of those solar driveway lights (for power) and send sensor data once every 15 minutes or something like that.