ADC Lightning Sensor fails very strange

XBee & XBee Gateway XBee - Zigbee
#1

Hi,

I have set up a Sensor for Temperature and Lightning - based on the “Building Wireless Sensor Networks”-Book which I love g

Config of my XBEE Router (AT Firmware - the latest).
PAN ID - same as concentrator :wink:
D0 - ADC
D1 - ADC
IR - FF

Everything else is (re)set up with the default settings of X-CTU.

On D0 i’ve added a LM35DZ - Thermistor (Thermal Sensor) - works great - I’m getting back values which look good.

On D1 i would add a Light-Sensor (like in the book mentioned above).

And there my problem begins…

If I reproduce the cabeling like in the book on page 105 (available on google books for reference), only difference: I only have an 22k resistor, but better more - than less:
BOTH D1 and D0 go up to 1023, if the sensor is in bright light.

If the lightning Sensor is dimmed light (holding my hand infront of the sensor) - the values look good.

My tries which all result in the same (both D’s up to 1023):

  • Adding more Resistors
  • Try the cabeling from ladyada (http://www.ladyada.net/learn/sensors/cds.html)
  • Reducing the current which comes from the source (from 4 Volts to 3 Volts)
  • Different Light Sensor (Same model - never used)
  • Different Radio

If i add a second LM35 (Thermistor) - it sends my a valid result back - the same as the other LM35

So I’m stucked and suffering for help from you…

Thanks in advance

Björn

#2

Are you sure, The output you are getting at the light sensor is Analog one?. I am sure that LM35 gives analog output thats why you are getting the perfect behaviour. Are you sure that are you providing differential voltage to the sensor, because I hope in normal case light sensor provides change in current. I hope you should provide differential voltage to the ADC pin of xbee. For that you may require I to V converter.

#3

yes it is analog acording to the documentation: http://www.produktinfo.conrad.com/datenblaetter/125000-149999/140374-da-01-en-FOTOWIDERSTAND_VT_93_N1_THT.pdf

It’s a VT900 Series.

I really don’t understand why this is happening…

#4

I think I found the solution:

When I’m using the power supply - the behavior is reproduce able.

If I use a battery as power source - the values are right - and keep continuously right…

So I think I need a better power supply…