Raspberry Pi Forums

Hi all,

first I must say sorry, this question might seem so simple but I am a software guy. Not really confident with hardware. I've been searching throught the forums and I've not seen anything similar, though it seems to me quite a common doubt. Also schematics mean nothing to me.
I am adding hardware to the Pi in order to get my project running.

I have a PiFace digital connected to the SPI bus:
http://www.piface.org.uk/products/piface_digital/

Also a AdaFruit PiTFT:
https://learn.adafruit.com/adafruit-pit ... i/assembly

I've read somewhere that the raspberry Pi can only control 2 SPI devices, so if I want to connect something else I should look for another interface (not SPI). Is that OK or I am going wrong?

I've connected both separately and programmed everything, worked great.
Now if I want to connect both, I should solder also the 2x13 IDC and attach a cable to the PiFace. This is what they say at the end of the webpage to connect an Adafruit Cobbler, I am going wrong?
Will the hardware address of the PiFace change when I connect both?

Regarding Power supply should I power the PiFace separately, would be the display and the PiFace too much for the Mini USB?

Now I have to add a GSM module, I have a USB dongle that can receive and send SMS but I must be able to make and receive calls.
I was thinking about the SIM900: http://www.pi-shop.ch/raspberry-pi-sim9 ... prs-add-on
But seems connected to the same place: http://www.pi-shop.ch/raspberry-pi-sim9 ... dapter-kit

Would be better to use the Adafruit FONA? If so wich connection?
uFL: https://www.adafruit.com/products/1946
SMA: https://www.adafruit.com/products/1963

As I understand this GSM devices communicate with the PI using UART interface. Then my question is, it is possible to add also a serial RS232 interface for V.24 communication with the Pi? If so, could you recommend me one, and tell me how to plug it in? Serial Pi, RaspiComm?

Finally, I would like to connect some digital sensors. Temperature, Fire / Smoke, etc ... Can I connect those directly to the Digital Inputs of the PiFace?

If I need an expansion board to connect all this together, can you recommend me one? I don't mind if you try to sell me yours, I don't mind buying your hardware, as long as you show me how to wire everything.

Sorry also for being so verbose and for my poor English.

jtorres wrote:Hi all,

I've read somewhere that the raspberry Pi can only control 2 SPI devices, so if I want to connect something else I should look for another interface (not SPI). Is that OK or I am going wrong?

SPI slaves require a Slave Selct or CS signal, the Pi has 2, supported by the driver.

For some background information:
http://en.wikipedia.org/wiki/Serial_Per ... erface_Bus

I2C is slower but can have many devices on the two wires, since I2C devices have addressses. Good to add sensors and such, not so good for devices requiring fast and lots of data like TFT displays.

Be aware of the 5V - 3.3V problems with I2C and SPI. Look for (very cleap) I2C level converters e.g. And keep the wires short or use twisted pair with ground lines.

http://www.raspberrypi.org/forums/viewt ... 35#p612835

This setup was for multiple DHT-22 using spi but you could use the same for normal SPI device. Just remove the diode and pull up resistor.


The other method will be to use a 74HC138 or 139 to make more chip select but some device always have the output always enable and won't work.

The 74HC4052 has the advantage to completely isolate the MISO and MOSI of each device.

This will allow you to add more SPI device.

Daniel

Hey!

For multiple devices, you might want to check out the RasPiComm+ as well (modular, advanced version of the RasPiComm). It is on indiegogo at the moment, giving you a chance to receive it before launch and save quite a bit in comparison to the retail price. And help us (I'm with the Amescon team) finance serial production

RasPiComm+ at Indiegogo


Cheers,
Rainer