Protecting startKIT I2C and 3.3V from 24V surge?
Posted: Sat Sep 10, 2016 10:07 pm
I am connecting an Adafruit MCP9808 I2C temperature sensor underneath my aquarium together with heating cable driven by 24V DC, pulsed by the startKIT. I connect SDA and SCL on MCP9808 to X0D23 (J72) and X0D22 (J73). It's powered by the 3V3 output. I2C doesn't need much speed.
Is there any way at all to protect the startKIT processor from a broken heating cable that hits the MCP9808? It would be ok for the MCP9808 to break, but rather not the startKIT.
I have simulated 300 Ohm in series with the SDL and SLC and 300 Ohm in series with the 3.3V, but I don't think it much useful. NXP advices this for SDA and SCL in their UM10204 "I2C-bus specification and user manual". MCP9808 has 10K pull-ups on SDA and SLC. I have not added any zeners. See attached PDF. I'm afraid it's too complex. It's not going to be in a rocket..
I have already made the layout such that during normal usage there's virtually no probability of any accidental 24V. The heating cable seems sturdy. I do this to monitor the max temp under there of some 50-60 DegC. The cable is 2 x 14 meters to spread out the effect, 2 x 24 W.
I haven't found any max ratings of the Tile 0 IO in the XS1-U16A-128-FB217 Datasheet.
I am tempted to let the connections just go unprotected. But in case there is a simple way?
Is there any way at all to protect the startKIT processor from a broken heating cable that hits the MCP9808? It would be ok for the MCP9808 to break, but rather not the startKIT.
I have simulated 300 Ohm in series with the SDL and SLC and 300 Ohm in series with the 3.3V, but I don't think it much useful. NXP advices this for SDA and SCL in their UM10204 "I2C-bus specification and user manual". MCP9808 has 10K pull-ups on SDA and SLC. I have not added any zeners. See attached PDF. I'm afraid it's too complex. It's not going to be in a rocket..
I have already made the layout such that during normal usage there's virtually no probability of any accidental 24V. The heating cable seems sturdy. I do this to monitor the max temp under there of some 50-60 DegC. The cable is 2 x 14 meters to spread out the effect, 2 x 24 W.
I haven't found any max ratings of the Tile 0 IO in the XS1-U16A-128-FB217 Datasheet.
I am tempted to let the connections just go unprotected. But in case there is a simple way?