Hi All,

Please advise me on scenario below as i have totally run out of idea:

I am intend to send my temperature result through wireless communication using the Wiznet wifi shield.
but i found that the reading is varied compared to the result that i send using serial port. (The serial port reading is accurate one).

I have measured the voltage across the LM35 when the Wiznet shield is applied. The reading is about 4.4V.
I take this as my reference voltage in my calculation.

Below is my code:


//declare variables
float tempC;
float inVol;
int tempPin = 0;
char buffer[25];

void setup()

void loop()
inVol = analogRead(tempPin);          //read the value from the sensor

tempC = (4.4 * inVol * 100.0)/1024.0;  //convert the analog data to temperature
delay(1000);                          //wait one second before sending new data

I tried to output the analog reading (Variable  inVol) for both serial and wireless communication.
But the weird finding is the  inVol give different result!!!! (54 for serial and 96.00 for wireless)
WHY?! i suppose it to be same since my circuit connection still the same and i just add on the wifi shield.

I am connection my system as below:
[b]Arduino Uno    Wiznet Wifishield[/b]
Rx            -  Rx
Tx            -  Tx
Gnd          -  Gnd
Vin            -  Vin  (I take out this connection for serial communication)

[b]Arduino Uno  LM35[/b]
5V            -  Vs
Gnd          -  Gnd
A0            -  Vout

please.... advise me what wrong with this...
I have totally run out of idea.

thank you very much

Hi Cielle,

First. You say that the voltage accros LM35 is 4.4v when Wifi shield applied. What about when its removed. Second how are you supplying power to your Arduino? This could be causing some problems.

Try to supply external power something like 7V is ideal. The difference in voltage from powering from USB or external power could be causing this irregularity.

Keep us posted on your results!