• Step 1: Ordering parts

    Stefan • 10/07/2020 at 04:02 • 0 comments

    After doing some more research I realized that the display I wanted is hard to come by, but the Siemens DL-430M is a bit easier to find and still has that great classic look of a bubble LED display.

    For the interface I really wanted something which doesn't take up too much room but still allows for fine control. There are some nice looking anodized aluminum knobs on sparkfun, but those take up too much real-estate. After some hunting, I found replacement knobs for Fender guitars which should do the trick:

    For the sensor there are so many options it took a very long time to narrow it down. Potentiometers are out because they don't provide relative sensing and are normally limited to a handful of turns. The PEC12R series of rotary encoders looks like a good match because I can get 24 steps per revolution and detents which give a nice clicking feel:

    I had originally been planning to put a selector button by each output, but there simply isn't room for three switches in front. Instead I'll add a switch next to the wheel. I was hoping to find something fancy to use for this button, but I may just end up using a plain old tactile switch I have in my parts bin.

    To actually control the LEDs I was originally planning to go with a 12-bit shift register produced by TI for driving LEDs (the TLC6C5912), but then realized that the outputs are open drain -- this means if I want to use them to drive the common cathode displays I got from ebay I would have to add inverter circuitry in addition to the current limiting resistors.  Instead I'm going to opt for the Max6950, which lets me use SPI to control 5 seven segment LEDs and I can set the current limit with a single resistor and capacitor. Nifty!

  • Step 0: Brainstorming

    Stefan • 10/05/2020 at 17:55 • 0 comments

    This project (re)started when I was cleaning out a closet and rediscovered my old electronics stash -- unfortunately I lost nearly all of the parts I had set aside for this when I first got the hydra in 2014! That's a longer story involving working in an badly maintained warehouse that eventually had a roof collapse that flooded the whole building.

    I want this project to produce something durable and easy on the eyes.  The idea is to add a bottom segment which attaches to the mounting holes provided by the hydra case. Back when sparkfun had the HP QDSP-6064 for sale I had gotten a couple and loved the look, so those are definitely going to be used for the displays. Ideally there will be one for each of the three outputs, but I may have to get creative there. 


    To set the value of each output I'm planning to use knobs, but I also want to keep the footprint small. The solution I'm hoping to come up with is to have a single knob or wheel on the side with buttons to select which output (if any) to adjust. Since adjustments are going to be relative, I'm looking at using a rotary encoder instead of a potentiometer.

    The other major change I want to introduce is to use a barrel jack instead of screw terminals for the input supply.  So to summarize on the outside we're looking at:

    * 1x knob to control voltage/current limits

    * 3x retro multi-digit seven segment displays 

    * 3x small push buttons on the front to select when to adjust the output value for each output

    * Barrel jack in the back for input power

    * A button to allow setting current limits

    On the inside, we're looking at:

    * 1x rotary encoder 

    * 3x display boards and drivers

    * 1x Arduino pro micro


    And of course, we want this to look cool, so let's throw in some LEDs.