Interfacing two "SPI" sensors with Arduino.

Hello everyone, I've having a little trouble getting two sensors to play nice together.

I've recently had success getting my MS5535C Barometric sensor working over in this thread:,90025.msg675730.html#msg675730 but now I'm trying to add a real time clock to the package and I'm stumped.

The RTC is Sparkfun's DeadOn RTC - DS3234 Breakout ( and I'm using the sample library written for it (

The trouble that I'm having is the MS5535C isn't a "true" SPI sensor, and doesn't have a Slave Select (SS) pin to tell it to shut up when the Arduino is trying to speak to the DS3234. My first thought was to simply turn the MS5535C off whenever I want to talk to the DS3234, but I'm at a loss as to how to do that effectively.

If you've got any suggestions, I'd be happy to hear from you! :)

Another option is to use software SPI to talk to the device that doesn't implement the Slave Select.

It doesn't take clocks in multiples of 8 so its not compatible with the hardware SPI at all - best to bit-bang it on different pins.