Lego Education Temperature Sensor 9749, how to access it?

[Maniac82]

Hello,

I am currently trying to read the values from an "Lego Education Temperature Sensor" with the product number 9749. It is not the yellow RCX Version.

I tried different configurations but only got 1023 as raw value.

I used the Lejos I2C detection sample but could not find any I2C sensors. According to this I think that it is not an I2C sensor.

Using the RCXTemperature.. gives me a temperature of -29,5°C what is definitiv not the right temperature in my living room

Can anyone give me some usefull links to more documentation or a code snippet? It would be a great help for me.

Thanks in advance

R.

[mattallen37]

It is indeed I2C. It isn't analog.

The reason you get 1023, is because the ADC doesn't get pulled down by any amount. The calculated "-29.5C" you get, is based on the raw reading of 1023 (no sensor affecting the ADC voltage).

[Maniac82]

Hi & thanks for the information.

Could you provide any further help? Documentation/Code-Snippet? That would be great. How can I find out the I2C-adress?

Thanks in advance.

[AndrejDelany]

Hi, I've the same problem. Does anyone have any idea how to fix this?

[mattallen37]

The chip used is the TI TMP275. Here is the datasheet. About half way down is the table of addresses. Instead of going to look for it, I'll post it here:

Address Pins and Slave Addresses for the TMP275
A2 A1 A0 -SLAVE ADDRESS
0- -0- -0- -1001000
0- -0- -1- -1001001
0- -1- -0- -1001010
0- -1- -1- -1001011
1- -0- -0- -1001100
1- -0- -1- -1001101
1- -1- -0- -1001110
1- -1- -1- -1001111

Or, like this: 1,0,0,1,A2,A1,A0.

I'm not sure how the address pins are configured in the lego sensor, but this should give you an idea of the address.

Sorry, I can't post any code for using it.

[skoehler]

May I point you to http://rdpartyrobotcdr.sourceforge.net/ ?
It's a RobotC driver suite which claims to support this sensor.

Somebody is currently trying to port this code to leJOS. I'll let you know if there's something to try.

[burti]

Hi.
I want to announce that Sven and I wrote code to access the temperature sensor.
I have tested it with my sensor and it works fine for me.
You can take temperature measurements with the four different accuracy levels.
However the one shot mode and shutdown mode are not supported yet.
You can find the code here:
http://lejos.svn.sourceforge.net/viewvc ... a?view=log

Enjoy it!
Michael