Hello All,

I built a small gadget that measures volatile organic compounds in the atmo=
sphere. I request you to have a look at the following video.

http://www.youtube.com/watch?v=3DIfEomgkK31M


The gadget glows green if the atmosphere is relatively clean and red if "po=
lluted".

I have attached a picture along with this mail. I have also attached a snap=
shot of the schematic and a picture of the gadget at this link:


http://mechatronicscraze.wordpress.com/my-air-gadget/


The problem is that the gadget shown in the left side of the attachment pic=
ture.jpg, when assembled into the enclosure on the right, the gadget seems =
to behave weird.=A0

The gadget interfaces a sensor and an LED that is operated via I2C interfac=
e. The problem is that the LED does not glow according to the instructions =
via I2C interface when assembled into the enclosure. Its behavior becomes e=
rratic after assembling into the enclosure. It plays the default script of =
the LED and obeys instructions from the microcontroller on certain instance=
s.

The microcontroller that is being used is a PIC AXE microcontroller. Someti=
mes, the LED gets stuck in a particular color and does not glow properly. W=
hen I take the circuit to the breadboard, I am not able to reproduce the pr=
oblem. I also observed the output on the I2C interface and there is definit=
ely data being sent as the gadget works properly on certain instances.

My theory for the LED getting stuck in a particular color is that the contr=
oller is getting reset and that this is happening due to the absence of cap=
acitors in the circuit. I am considering adding capacitors across the LED a=
nd the microcontroller and at the input. My theory for the LED playing the =
default script is that the current draw for I2C communication interface is =
low. I am using a 1K pull up resistor on the SCL and SDA lines. I read an a=
rticle that it should be at least 1.8K. But I am not able to prove it as th=
e gadget works sometimes for 1K resistance.

I would like to hear your thoughts on the erratic behavior of the enclosure=
 when operated using a battery and mounted inside an enclosure.

Regards,
Sai
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