SparkFun Forums

[emeyeraway]

I have successfully connected a SEN-11931 Temperature Sensor (from SparkFun) to my RasPi and can log temperatures over time. I would like to connect two of these sensors at the same time. My problem is, how do I use a different address for the second sensor? Connecting the address pin (ADD0) to ground provides the address for the first sensor. I found something on the internet that says connecting the ADD0 pin to 3.3V should change the sensor's address, but when I try this, my RasPi crashes; i.e., the little red light goes dark. I was relieved to find that it doesn't seem damaged by the experience.

Can someone tell me how to connect a second SEN-11931 sensor to a different address in RasPi?

Ed Meyer

[DanV]

If you notice on the board, there appears to be a solder bridge on a couple pads on the board. You would likely de-solder the bridge and re-solder to the other pad.
If you simply pulled the pin along the board edge to 3.3V, you shorted the power supply coming into the board (but you didn't hurt the RasPi).
Have a close look at the board and you can see what I mean:
https://www.sparkfun.com/products/11931

[emeyeraway]

I did what you suggested, using a continuity tester to make sure I had broken the bridge and connected the middle pad to the other pad. Making all the same connections as before, the RasPi light does not come on when I power up. Any ideas?

[Valen]

Does the RasPi work correctly when you do not have these temp sensors connected? That should isolate the fault to either your solderbridge removal, or something on the RasPi, possibly a damaged 3.3 volt regulation.

[emeyeraway]

Yes, the RasPi works OK now with my one sensor. But first I went back and removed the new solder bridge I had made. I think I may have damaged the middle pad in the process, because now only one of the four addresses that are supposed to be available to the sensor actually works. I think the resoldering idea was a bad one, and I shouldn't have done it. But at least now I'm back where I started, i.e., when the ADD0 pin is connected to GND, the sensor works fine.

[Valen]

Well, you can still use a pull-up (or pull-down) resistor soldered between the ad0 broken out pin on the side, to vcc (or gnd).

[emeyeraway]

I don't know what this means.
Ed Meyer

[Valen]

This is what is meant with a pull-up resistor:

https://learn.sparkfun.com/tutorials/pull-up-resistors

A pull-down resistor is the same but the resistor is then connected to Ground instead of the positive voltage.

BUT, when I wrote that I didn't read the datasheet well enough about how this ADD0 pin works. I thought it was a simple digital input. But apparently it can also select 2 more addresses by connecting it to SDA or SCL. (Which the solder jumper on the board doesn't allow you to choose) So, now I am not sure if adding a resistor in that path disrupts the address selection circuit. So please disregard my idea. Instead make sure there is no conductive path between the damaged center solderpad and the adjacent ones. Then bridge the ADD0 pin on the side of the board to Vcc or GND as needed for the desired address.

If you want to remove solder from a board I suggest you use that solder wick/braid stuff. It really soaks up the excess solder when it gets hot and leaves a nice clean solder pad. Always check for conductivity with a multimeter set to continuity or resistance mode to make sure your work was successful.