U.RAT Key Learnings
Here are some key design notes and learnings:
- I had to use a Raspberry Pi due to the fact that the KPOD driver software is written in C and compiled on Linux.
- The KPOD is a proprietary device using the HIDRAW protocol, so its not exactly the same as a keyboard or mouse
- The WiringPi library turns the interfacing part between software and pin outs on the RaspberryPi into basically a “virtual Arduino”. This makes it amazingly simple to use the Raspi GPIO interface / pins
- I do not need the Enable positive or negative lines from the TB6600 drivers
- The TB6600 drivers are probably overkill, but they represent good engineering and stay cool no matter what
- The delay in the program and the DIP switches on the drivers are what set the steppers in the right “zone” as far as response from the KPOD. The DIP switches are – (1 – 6): U,D,D,D,U,U
- The wiring of the drivers is very easy – all grounds are ganged, and the 3.3 and 5V grounds are tied together – meaning one ground wire for everything is all that is needed. Then, only two wires are needed from the drivers – one for direction (DIR) and one for step (PUL).
- I’m splitting the system in two – drivers and steppers out at the tuner and everything else in the shack. Since I will use a 12v to 5V regulated and filtered step down gizmo to supply 5V to the Raspi off of a 12V supply, the 5V stays in the shack and 12v goes out to the tuner. This means 12V + and – wires and 4 wires for the drivers total. Add in two wires for the kill switches and you get exactly 8 wires needed from the control box in the shack to the tuner box
- The Palstar BT1500A is a truly amazing balanced line tuner. It offers pretty much every configurable setting for all low bands with an antenna that is resonant on 160M but used also on 80, 40 and 30. Since the SPE Expert 1.3K FA amplifier requires a low SWR, the Palstar tuner is exactly the right tuner. I did remember to bypass the SPE internal ATU for 160, 80 and 30M, which are the bands the Mod Bob and Palstar will be used on. I do use the ATU in the SPE on my DXE 40M phased array and my 20M homebrew 2 element yagi
- The Mod Bob is the most amazing low band antenna I have used because it covers low bands with very respectable performance – and this is the “holy grail” of antennas. I never expected to finally get a bastardized Bobtail Curtain to work so well. I tried feeding Bobtails twice before against ground and they seemed no better than a single vertical. HOWEVER, this open wire balanced line fed antenna models great and plays better than expected. Sure – a dipole up a half wave, but I can only get a dipole 1/2 wl on 30M, so I’d have a cloud warmer on all of the lower bands. This is where what I read on Tom, W8JI’s web site has to be put in context. Yes, I would always choose one or more elements up 1/2 wl over any vertical, but, to do what I have done on the low bands (and given my crappy terrain down here in the bowl), I truly believe I have conquered the problem with flying colors
- The URAT consumes .75 amps with no load – once I have the variable capacitor and the roller inductor added, I will be able to see the current draw with my variable bench supply. Now I see why a variable bench supply is so important – besides setting current limiting on the stepper drivers (so you don’t burn the drivers up or run them over heated), you can protect what you plug into the supply voltage and current wise. Then, you can monitor how much current the steppers are drawing under load and not under load
- The Raspberry Pi Zero W plus Adafruit Pi-OLED is the absolute perfect device for the processor part of this project – small and has exactly what you need – not a thing more. A VERY elegant design
- The KPOD can be marketed to the much larger Maker community. It is a wonderful ham radio shack automation controller – and its applications above and beyond the URAT seem only limited by your imagination
- I think I am having the most fun I have ever had in electronics and ham radio. This Maker World has expanded my world so far past just sitting in the shack waiting for the next ATNO that its not even funny. I feel like I used to just be an ATNO junkie . . . “Hands on Ham Radio” is my rehab. To be fair – building antennas used to be my rehab – but I’ve run the gamut on that
- I won’t be working on any more DX-peditions, but will instead be making stuff in my shack / lab
- I feel that just doing my first Maker project that its as important as Honor Roll and DX-pedition of the Year. I don’t know why – this is totally an emotional response
- If the steppers don’t draw more than twice what they under no load, it might have been possible to use the Adafruit Pi Hat Motor Shield – which is rated at 1.2 amps per stepper, HOWEVER, because the drivers will go out with the steppers in the tuner box – the Adafruit hat doesn’t work for this configuration. For another project it will be perfect – perhaps with the Nema 17 steppers I have – since they are lighter duty but still quite strong. I felt the NEMA 23’s were best for the torque needed for the L and C components
- When I explained the difference between the Raspberry Pi and Arduino, she asked “Why would you even bother with the Arduino?” That’s a very good question, since the Raspi Zero W costs only $26 and the Arduino – $18.82 (official units not cheap knock offs)
- Writing code for embedded devices is just too much fun – and my C and Python background were both very important. Also – having been an Oracle DBA on UNIX and Linux meant that I had no learning curve with what might be the most technical part of the project. The electronics part is about 8th grade science fair level – the software part a little higher – but kids these days take to this stuff very quickly – don’t underestimate them. Great memories of 1971 building my first Heathkit come rushing back
- I feel like I can be a product designer now – its an awesome feeling – like I can do anything
So – how much is this experience worth in dollars?