Beinger looking for a Chip

Discussion in 'Electronics Resources' started by pyromanci, Sep 5, 2014.

  1. pyromanci

    Thread Starter New Member

    Jul 25, 2012

    I do programming and I have a project I'm working on that requires me to be testing with several different types of SPI interfaced devices. I'm reading and write data to them. Each time i need to test or check one of the other device, it becomes a pain to disconnect the current one and connect the other.

    So I thought I would just make a small circuit board that would let have the 4 devices connected to it and then connect the other end to my computer and just use a "dip" switch to flip between the devices. Problem is I'm still very new to electronics and only know mostly basics. Either I'm not reading things right in spec sheets or i just havn't come across the right chip yet.

    So I'm hoping some one can help me locate a ic/logic chip (or chips) that will let me do this. I did make up a little schematic of what I'm asking for in case i'm not making sense.
  2. MrChips


    Oct 2, 2009
    SPI uses four signals:

    MOSI - Master Out/Slave In
    MISO - Master In/Slave Out
    SCLK - Serial Clock, output from master
    SS' - Slave Select (inverted)

    You can connect MOSI, MISO and SCLK from master to all slaves in parallel.
    You need a decoder circuit such as 74LS138 (TTL) or MC14556 (CMOS) so that only one SS' is active (LOW) at any given time, or you can use DIP switches to connect the desire slave SS' to GND (with pull-up resistors on all SS').
  3. pyromanci

    Thread Starter New Member

    Jul 25, 2012
    I didn't think I was going to need cmos style chip, but more something akin to a solid state relay. Since the SPI devices were not being really run in parallel. Each 1 needed to be powered off while the other is in use.