LM35 on the energia.

[Indian_villager 0]

Hey all,

 

I'm relatively new to all this and I have been trying to get a temperature sensor to work with the launchpad. As in my previous posts I was trying for the DS18b20. I have the port of the code project on the back burner because there is a hell of a lot I need to learn to be able to port that over.

 

So just to get something off the ground I have been trying to use the LM35 to read some temps.

 

Here is the code I'm running

 

float tempC;

float tempF;

 

void setup()

{

Serial.begin(9600);

}

 

void loop()

{

tempC = analogRead(6); //read the value from the sensor hooked up to pin 6

tempC = (3.3 * tempC * 100.0)/1024.0; //convert the analog data to temperature (Assuming 10bit ADC and 3.3v ref voltage

I suspect this is where I'm screwing up)

tempF = ((9.0*tempC)/5.0)+32.0;

Serial.println(tempC);

Serial.println("");

Serial.println(tempF);

Serial.println("");

delay(1000);

}

 

The issue is that It is showing very high values. Like the order of 178 c?

I also tried chaning the tempC calculation to

 

tempC = (tempC*100.0)/1024.0

 

It gets closer but still not quite.

 

(I'm monitoring through the serial monitor and I have not made any changes to the jumper position to my 1.4 board)

 

 

Any and all help is appreciated.

 

 

Regards,

Alex

[Rei Vilo 695]

There is an interesting tutorial about the LM35 and related formulas and problems at http://learn.adafrui...perature-sensor

[Indian_villager 0]

So here is something screwy.

 

When I try to use pins 4 or 5 as the input i see random outputs

 

when I use 15 or 14 the temp read 0C or 32F...... I have no idea what is going on. I checked my lines and I dont have anything shorted.

 

FYI I am using a MSP430G2452

 

Regards,

 

Alex J

[calinp 24]

For analogread use the analog input number: 6 is the same as A6, but is on pin 14, not 6.

[Indian_villager 0]

After a bit of digging I have found 2 issues.

 

The LM35 needs a minimum of 4V so I dont think the rail is waking it up.

 

Also the chip I have does not have a proper Hardware UART setup, so I think I am going to have to switch up to a the G2553. Any thoughts?

 

Ref:

https://github.com/energia/Energia/wiki/Serial-Communication#wiki-Hardware_UART_on_Launchpad_14

 

Regards,

 

Alex J

[Rei Vilo 695]

For the mapping of the pins, see the hi-res pictures at https://github.com/energia/Energia/wiki/Hardware

 

Each picture takes into account the MSP430 model and the revision of the board, 1.4 or 1.5.

 

I hope this could help you.

[Indian_villager 0]

I've already seen that and it is what I have been using, what I think the issue is, is that the G2452 does not have an onboard UART. I am hoping that someone can confirm or deny.

 

 

Regards,

 

Alex J

[cde 334]

It does not have the usci uart/spi/i2c, it has a usi spi/i2c. Energia compiles a software uart for it instead (using a timer).

[Indian_villager 0]

.....Well then. I am at a loss.

[traxman 23]

...The LM35 needs a minimum of 4V so I dont think the rail is waking it up.

 

Try LM61, pinout is identical, but LM61 works with lower supply > 2,7V

[calinp 24]

Is your temperature reading improved if you connect LM35 to the phisical pin 2 and read it with analogread(A0)?

You can supply the sensor with 5V from TP1(USB 5V) and TP3(GND).

[Rei Vilo 695]

I've already seen that and it is what I have been using, what I think the issue is, is that the G2452 does not have an onboard UART. I am hoping that someone can confirm or deny.

 

That's correct. The serial port is managed by the software UART TimerSerial library. See an example at https://github.com/energia/Energia/blob/master/examples/4.Communication/Serial_430/Serial_430.ino