Raduino Pill – All Systems Now Running

30 Aug

Today I got the Si5351 running, so all the sub systems (LCD, encoder, Si5351) are now operating. Next step is to see if I can build stock uBitX code to run on the new platform.


Raduino Pill

27 Aug

The board is now working with the stock LCD and encoder. Next step is to test out the Si5351 circuits, then convert the stock uBitX20 firmware and see if I can make the whole radio play like it did with the original Raduino board.

Some Progress on Raduino Pill

23 Aug

I was off this project for a long time while I attended to some business matters. I got some time the past couple days to get back to it.

The voltage regulators are running, the LCD is connected and the Si5351 circuitry is soldered but not tested. I spent quite a while trying to figure out why I couldn’t get the LCD working with a simple “Hello World” sketch, only to finally discover that a tiny 1/32″ long piece of PCB trace between a via and an LCD connector pin was missing. I probably knocked it off when I was soldering the LCD connector…it’s only 6 mils thick, so very fragile. I’ll fix it later today and I expect the display to fire right up.

Next step will be either the encoder or the Si5351 – I haven’t decided yet. Hopefully I’ll make steady, if slow, progress from this point. Once the 3 main subsystems are working, I’ll try to convert stock uBitX firmware to run on the new platform. After that, I’ll start working on migrating the upgrades I had on the original Nano version over to the new Blue Pill processor.



Update: 8/24:

There were actually 2 problems. The broken trace I mentioned and a mislabeled port on the schematic. The first was fixed with a wire; the second was easily fixed with an assignment change in the sketch.

Seems to work now.  Next step, get the encoder working.

SWR Bridge

12 Aug

This term really bugs me, as none of common designs are really measuring SWR (“Standing Waves”), they’re measuring the error ratio of an actual impedance compared to a reference. If they were really measuring standing waves, which they can’t be doing  because they measure even if connected directly to a load with no transmission line, the SWR on the transmission line would be assumed to be the ratio of the known impedance to the reference impedance. For example, in a 50 ohm system, a 2:1 impedance mismatch (25 ohms or 100 ohms) would correspond to a 2:1 SWR. This is another soapbox matter for another day.

Anyway, I designed this little board to go on the SO-239 connector of my uBitX transceiver and drive an A-d converter input. If there’s interest, I’ll publish the DipTrace CAD files and Gerbers and/or make it available directly from the board fab house. Seems to work, with over 20dB of directivity without any adjustments. This was with 100mW from my HP8640 signal generator. Calibration with power needs to be developed. Insertion loss is less than 0.2dB and input match is better that 20 dB & seems pretty flat over the HF range, but I don’t have any detailed numeric or other real-world data at other power levels to publish at this point. I’ll publish more as I characterize it, but got to get back on the Raduino Pill first.

SWR Bridge Schematic (pdf)

The schematic is from LTSpice, so you can run the simulation if you like.

Note that the ratio of R1 to R3 & R4 sets the full-scale DC output voltage. I have the values set to get about 3.3V @ 10 watts, which is right for the A-D converter on the Blue Pill board.

This is a sweep of the reverse port made with my Tektronix 495P analyzer w/tracking generator. Note that the sweep is referenced to the second graticule line from the top. 

Building the Raduino Pill

30 Jul

I got some time this weekend to start building the board. After a struggle with the power section because I laid out the board for a 3.3V regulator that I didn’t have on hand and a similar issue with the Si5351 crystal, I managed to kludge in other parts that seem to work. The Pill board is showing signs of life and the LCD display lights up. This week, I’ll start converting the stock uBitX-20a code to run on it.

View of voltage regulators, power management and Si5351

Raudio Pill with LCD


Raduino Pill

20 Jul

In my quest to tailor the uBitX transceiver to my liking, I ran into some bottlenecks related to speed and memory limitation in the Arduino Nano board that’s the heart of the Raduino.

I developed my own expanded version of the Raduino using an inexpensive (~ $2-$3) “Blue Pill” board that’s very common on Ebay and other sites. This is a 32-bit ARM processor board that runs in excess of 70 mhz and has 128K of flash memory. It’s a footprint-compatible replacement for the Nano but, due to the different I/O complement, some of the pin assignments are different. This board should easily run the uBitX with all the fancy peripherals and features I want to incorporate. I’m calling this new Raduino incarnation the “Raduino Pill”.

The PCB boards have arrived and I’ll be posting updates here as I make progress building and programming it. I’ll also post schematics, CAD files and Gerber files, and I’ll make the board open to purchase directly from the PCB fab house.

Raduino Pill Board

The first step of the process will be to mount the voltage regulators, the Pill board and the stock LCD to test for signs of life. Then I’ll convert the stock uBitX code to run on the new platform. After that, I’ll incrementally add hardware and software features. Code will be available on this site and on the Google I/O Bitx20 group files section under “W3JDR”.


uBitx Dynamic Range Improvement

11 Apr

The audio preamp (Q70) in the uBitx isn’t biased optimally and therefore overloads about 10 dB sooner than it should. As it comes from the factory this stage, which is powered from 12vdc, is biased to about 1.6v at the collector. For best large signal handling, it should be biased to 5v or 6v. This is easy to fix by adding a 16K (optimum value; 15K will work) from base to ground. This is very convenient to do with a SMD resistor, but a leaded part can also be used. I’ll post a picture when I get a chance.

My software-derived S-meter is now working very, very nicely with no hardware and no hickups. I moved away from the continuous-conversion interrupt-driven ADC to a timer interrupt based ADC that converts about 3900 times per second. It has very fast attack and software definable decay. I implemented a table-driven logarithmic compression function so I can calibrate the meter in S units. Right now it drives a moving-bar meter on the main TFT display (see the pictures below), but I’ll eventually add a dedicated smaller TFT just for the S-meter and other metering functions. Next I plan to add an I2C digipot in place of the volume control. This will allow the S-meter function to control the volume as a software controlled AGC. I also fine-tuned the 400 ppr encoder so that no step-size selector is required. When you turn the knob very slowly, it tunes in 1 hZ steps, accelerating to 2, 3, 5, 10, 25, 50 and 100 hZ steps as you spin the knob faster. You can smoothly tune in a CW or SSB signal, but also quickly traverse the whole band in a few revolutions when you wish. It feels like an expensive radio.