SDR-2017: More Controlling the Beast

The diagram (and board) are starting to fill-out nicely! I've added a couple of things since my last post:  Outputs for the cooling fan for the Pi and for switching the low-pass and band-pass filters.

The fan output is straightforward:  I use a 47 Ohm wire-wound resistor to drop the voltage and slow the speed a bit, and a 470 uF capacitor to eliminate any electrical noise. Easy peasy.

The filter select lines were slightly more involved.  Since the Arduino will always be aware of the frequency of operation, I added some conditional statements within the sketch to activate the appropriate filter-select lines based on that frequency. To conserve the Arduino's I/O, I'm using a 74AHCT138 3 to 8 bit decoder.  I'll throw-up (unfortunate choice of words) the code sometime in the next day or two.

While this version of board and code are doing their intended duties, they're still very much in the preliminary "proof of concept" stage; I may want the Arduino to perform some other tasks, such as a CW Keyer, that rely on pin-change interrupts, so I need to look at my port choices to work around the interrupt limitations of the Arduino.  Right now, the only interrupt-driven thing we're doing is reading the encoder, so it's not an issue...

73!