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Re: Xbee Wireless Temperature Sensor

by adafruit on Mon Nov 16, 2009 3:46 pm

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 :)
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Re: Xbee Wireless Temperature Sensor

by Pelphry17 on Wed Dec 02, 2009 11:22 pm

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 | TOGGLE FULL SIZE
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)         
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Re: Xbee Wireless Temperature Sensor

by adafruit on Thu Dec 03, 2009 3:14 pm

whats the 10bit value returned? does that vary?
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Re: Xbee Wireless Temperature Sensor

by Pelphry17 on Thu Dec 03, 2009 7:02 pm

Yes, the "mVolts" is changing from around 85 to over 130. The actual temp outside is 19F.
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Re: Xbee Wireless Temperature Sensor

by adafruit on Thu Dec 03, 2009 9:40 pm

ok, use a multimeter to measure the voltage from the TMP36 as it goes into the ADC
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Re: Xbee Wireless Temperature Sensor

by Pelphry17 on Fri Dec 04, 2009 2:32 pm

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?
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Re: Xbee Wireless Temperature Sensor

by adafruit on Fri Dec 04, 2009 4:12 pm

150mv is -a lot- of ripple. you really need a LDO or just batteries. really! :)
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Re: Xbee Wireless Temperature Sensor

by FlyingSaucrDude on Wed Dec 16, 2009 11:01 pm

Does anyone still have the pictures showing the wiring stashed somewhere? Flickr doesn't seem to have them anymore...
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Re: Xbee Wireless Temperature Sensor

by zachschi on Mon Dec 20, 2010 12:29 am

Hello, I second that, any images still hosted out there? I would be willing to host them also. Thanks.
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Re: Xbee Wireless Temperature Sensor

by zard on Fri Sep 07, 2012 10:54 am

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
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Re: Xbee Wireless Temperature Sensor

by adafruit_support_rick on Fri Sep 07, 2012 11:17 am

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
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Re: Xbee Wireless Temperature Sensor

by Lawndart on Tue Jan 29, 2013 11:18 pm

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.
Image
Image
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.
Image
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