Analog ADT7420FBZ Question

Hi Joshua,

From what I can tell, the eval board doesn't have pull-ups, and I've no idea if the RPI has pull-ups, but I suspect it doesn't. In that case, you'll need a couple of resistors, i.e. something like 2.7k resistors from the SDA and SCL lines to +3.3V will be needed.

Good luck with your project!

I have 1k ohm, not sure about 2k.

The SDA and SCL pins are floating, and need to be connected to +3.3V using resistors, i.e. basically something like this (and repeat for the SCL line too). And connect the 0V line between the board and the RPI too.

1k is a bit low, something between 2k and 5k is good. If you don't have this, use (say) two 10k resistors in parallel to get you 5k, or two 1k resistors in series to give you 2k.

Great, thank you. I'll give this a try once I have some 2k-5k resistors and I'll let you know how it goes. Marking as helpful for now

ummm... i am not sure, but i think pi B has 1.8k pull ups for i2c lines. i don't know about pi B+. however, u can give it a try and let us know.

7420 suggests typically 10k for interfacing.

Edit ->

for B+

I2C1_SDA and I2C1_SCL pins 3 and 5 of the GPIO header should be used and they are pulled up with 1.8k. I2C0 [GPIO's 28 and 29 (SDA0 and SCL0)] has pull up resistors but is occupied by camera interface. ID_SD and ID_SC is used for EEPROM which does not have pull up resistors. So if ID_SC and ID_SD are used then external pull ups are needed.

Ahh you're right. Sorry Joshua for leading you down the wrong path.

I can see it described here: http://www.raspberrypi.org/forums/viewtopic.php?f=44&t=7664

(there are no schematics for the RPI to confirm this for ourselves).

Looks like the issue is something else : (

If you can post a photo or description of what pins you've connected up, perhaps something can be spotted, but it seems you're doing the right thing if you've connected up the SDA and SCL pins on the RPI to the correct pins on the board, and connected up 0V together between the RPI and the board, and provided the supply (which could also be taken from the RPI).

I have the module connected as follows:

I don't have a photo yet but I'll try and get one taken tomorrow. Thanks for your help, everyone.

EDIT: Adjusted Pin Name above in regards to the comment below

Hi Joshua,

Did you really mean GPIO5, or did you mean pin5?

The clock should be connected to pin5, i.e. GPIO03. Could you confirm this is what you've got?

Similarly for Data, that should be pin3, i.e. GPIO02.

These are the blue pins in the image below.

Apologies, yes. I was following a different diagram.

Apologies, yes. I was following a different diagram.