Raspberry Pi with Buffer Pi

[Loonhaunt]

I just set up my Pi with PiFace, am planning on using it to run SainSmart 8 relay board. I am wondering if anyone has used AB Electronics Buffer Pi between the PiFace and the Pi? Of i a buffer should live between the Piface and the SainSmart Board? I don't know if there is any code involved with installing the Buffer Pi. If not, It should not make a difference where it is located. If between the Pi and the Pfiace then at least the Pi is protected. Is that correct?

Dave

[Paul Moir]

Should be no problem. You might want to disable the relays on the PiFace so you can use all 8 on the other board. There are only 8 output drivers and two are used for the relays on the PiFace.

Looks like your SainSmart board has optocouplers, so I don't see much point in using a buffer board. At say 10ma per channel to light the leds, that's only ~80ma, which is well under the piFace's ULN2803A's 2.5A total theoretical maximum. (Note that this output driver can sink fairly high voltages > 5v as long as JP4 is removed from the PiFace which would backfeed higher voltages into the 5v line possibly destroying things. Unfortunately the LED indicator implementation on the piFace prohibits using voltages higher than ~12v since using a reverse biased LED is a *really* bad idea. And even using 12v you would be wise to remove the LEDs.)

It's possible to reconfigure the inputs as outputs for extra channels, but this will take some doing, level shifting the 3.3v MCP23S17 or modifying the SainSmart board to work at 3.3v.