Monday, October 15, 2012

Interface Nearly Complete

After far too many revisions, the GPIO interface for the Raspberry Pi alarm system is nearly done.  It has:

• 8   Digital Inputs
• 4   Relays
• 1   RS-232 serial port
• 2   SPI bus connectors
• 1   I2C bus connector (eventually)

I still need to to finish wiring the SPI connectors, but the serial port, the digital inputs, and the relays are all working.  I will probably go ahead and add connectors for the I2C bus pins for future use.  I already have an eight port A/D converter for the SPI bus and more GPIO would also be easy to add via SPI.

I added a jumper block near the GPIO connector that allows me to connect (or not) 5V on the interface to 5V on the RasPi.  This would allow me to power the board from the RasPi or to backfeed power to the RasPi from the board.  I plan on making a jumper with a polyfuse inline.  Using that as the jumper will prevent the  RasPi from drawing too much current.


  1. awesome man! can't wait to see it finished!

    1. Thanks. I will post some pictures next week when it is all together. Hopefully I won't have any drastic changes once I get the SPI bus wiring finalized. I will probably leave the I2C circuit off for now since I really want to get this thing hooked up.

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  4. really good job till now i use raspberry only for collecting temperatures with ds18b20 on 1-wire but i'm still looking for such board as yours

  5. I have an old security system where the board is fried and I'd like to take a stab at this security system portion of this project.

    I have 8 magnetic switches for doors and windows, and 1 motion detector but I think I can't use that because we have cats. Can I wire multiple contacts into 1 input as a series circuit? I'm not concerned with zones.. -it'll either be on or off.

    In the picture above, it looks like the digital inputs are only the stuff located on this front corner of the board? Is that including the opto-coupler circuit and also the multiplexer design you wrote about? So the multiplexer serves the 2 opto-coupler chips?

    Any help you could offer would be appreciated because I'm looking to wing it here as an electronics novice. (I'm more comfortable in the software side)