Connect more than 6 DAC using Raspberry Pi 2

Question

How can I connect more than 5 or 6 MCP4922 DAC using Raspberry Pi 2 Model B, if it is possible?

I saw SPI SDA GPIO Rspi.

Answer 1

There are many ways.

I'd say the simplest is just to ignore the slave select signals used by the SPI driver and use your own.

E.g. say you have 6 DACs.

Find 6 spare GPIO. Let's say you use 22, 23, 24, 25, 5, and 6 (chosen as they are not used by SPI).

Connect DAC 1 slave select to 22
Connect DAC 2 slave select to 23
Connect DAC 3 slave select to 24
Connect DAC 4 slave select to 25
Connect DAC 5 slave select to 5
Connect DAC 6 slave select to 6

Write 1 to all those GPIO to deselect the DAC.

Connect the other SPI lines normally (i.e. MISO, MOSI, SCLK).

Then to talk to, say, DAC 4, write 0 to GPIO 25 to select DAC 4, call the SPI functions you want, write 1 to GPIO 25 to deselect DAC 4.

Repeat as needed for the other DACs.

---

E.g. in pigpio terms

h = pi.spi_open(0, 100000) # Get handle for all DACs at 100kbps.
                           # Use any legal channel, it will not be used.
...
# Write to DAC2
pi.write(23, 0) # Select DAC2.
pi.spi_xfer(h, [0, 95]) # Set DAC2 channel 0 to 95.
pi.write(23, 1) # Deselect DAC2.
...