several SPI devices with diffrent bus voltage

Projects Networking, Protocols, and Devices
1

I connected several SPI devices to an arduino due. 2 modules i connected over a level shifter from adafruit ( the one with the FETs and Pullups, BSS138 PRODUCT ID: 757) to 5 Volt. It is a SD-Card (MicroSD card breakout board+ PRODUCT ID: 254 ) and an AD5231 a digital potentiometer. The CS/SS also goes through a level shifter. This works fine and im happy with it.

Now i have a bluetooth module from adafruit (Adafruit Bluefruit LE SPI Friend - Bluetooth Low Energy (BLE) PRODUCT ID: 2633 ). I thought i could connect it directly to the 3,3v bus side of SPI. since it is 3,3v capable. But it doesnt work. It works only when i remove the level shifter completly from the board an with it the communicatin to the other 2 modules. Please see the attached diagram.

I tried a lot but nothing helped. For instance: I tested all 8 possible CS/SS H/L settings.

Is there a way to make it work? When not, what it the reason that it doesnt?

I would be happy to hear your insigth or from further tests which i could do.

Thank you.

spi.png
spi.png1280×720 12.1 KB

2

The picture doesn't help. The bluetooth module is 5v. Maybe that is your only problem. I believe the Due has 5v available.

3

Is there a way to make it work? When not, what it the reason that it doesnt?

You need a more elaborated level converter. The problem is the MISO line. If the CS line is HIGH, the MISO line must be in a high impedance state and pulled high as your level shifter is doing it. A MAX3375 has a three-state mode and might be used.