jugando con Arduino

youtu.be/y0mCjXQiuFI?si=AMafwN…

#arduino #si5351 #ham #radio #radioaficionado #vfo #dds

Also called a “DDS VFO.” This may be a bit of a brain dump. Although I have local notes (in Joplin), if I had to look hard for this stuff, maybe someone else can benefit from it. I’ll try to skip the details of the dead-ends I went down.

I put the Pixie kit I put together as a distraction from the thing that’s been bugging me, which is putting together some different modules in a receiver to 1) learn more about hardware and b) eventually design a radio orienteering receiver. (Why design when I can put together someone else’s design? Not sure yet.)

Building

In short, I took these building blocks and put them together:

• Adafruit Si5351 breakout board to act as a local oscillator
• Adafruit Metro microcontroller development board
• Pretty generic OLED display (pulled from a TTGO T-Beam I originally got on AliExpress)
• Arduino code from CesarSound
• Pixie kit from AliExpress
• Rotary encoder with push button from eBay
• Generic momentary contact button (originally from SparkFun kit)
• High-pass filter that I designed and need to blog about

Although I don’t understand it all yet, the modification to the Pixie is explained at the very end of this “S-Pixie QRP Kit Student Manual.” Although I have the Pixie and not the S[uper]-Pixie, the component names matched the schematic I was provided with.

The S-Pixie can be modified to cover the whole 40 Meter band by replacing the oscillator with a VFO. A popular approach has been to use a Direct Digital Synthesizer (DDS) controlled by an Arduino. The human interface includes an LCD display and rotary encoder.
Popular DDS choices include the AD9850 and the SI5351.
Remove/Omit C3, C7, Y1, W1, D2, R6, and C8.
Place a 47K resistor between Q1 base and GND.
Connect the DDS across that resistor.

I don’t think I changed any of the code yet, but my version is here. I used the same pins CesarSound defined in the schematic below. I only used the connections from the Si5351 module, the OLED display, and the rotary encoder to the Arduino and ignored the rest. I skipped the capacitors across the rotary encoder connections.

Testing

I’m a bit overwhelmed, so you don’t get anything here right now.

here is where I talk about testing, maybe with audio/video

does it transmit

HPF to block broadcast AM – separate blog post

not great selectivity – hard to use for QSO

Next Steps

I have to keep reminding myself that this is not a product, it is a learning exercise. I do plan on making a standalone digital VFO module (with a board and case and all that) that can be plugged into other modules as needed. The digital VFO might use something smaller and cheaper than the Metro, like an ESP32 dev board, if I can get it to work. Pete N6QW has a bunch of information on this type of project.

The Pixie part may be modified/stripped down more so I can better understand it or re-use into another application.

Photos

https://w1cdn.net/2024/02/pixie-with-digital-vfo/

#arduino #hamRadio #homebrew #kit #pixie #si5351 #vfo

Boat Anchor Twins Get a Little Digital Help Staying on Frequency

In the ham radio trade, gear such as the old Drake units [Dr. Scott M. Baker] has in his radio shack are often referred to as "boat anchors." It refers to big, heavy radios that were perhaps a bit overengineered compared to the state of the art at the time they were designed, and it's actually a shame that the name has taken on something of a pejorative connotation, since some of this gear is rock solid half a century or more after it was built.

But older gear is often harder to use, at least compared to the newer radios with microcontrollers and more stable oscillators inside. To make his 1970s-era Drake "Twins" setup of separate but linked receiver and transmitter a little more fun to use, [Scott] came up with this neat Raspberry Pi-based DDS-VFO project to keep his boat anchors afloat. Compared to the original mechanically tuned variable frequency oscillator in the Drake receiver, the direct-digital synthesis method promises more stability, meaning less knob-nudging to stay on frequency.

The hardware used for the DDS-VFO is actually pretty simple -- just a Raspberry Pi Zero W driving an AD9850-based signal-generator module. Sending the signal to the Twins was another matter. That was done by tapping into the injection cable linking both units, which meant a few circuit complications to deal with signal attenuation. [Scott] also added amenities like a digital frequency display, optical encoder with crank-style knob to change frequency, and a host of Cherry MX keyswitches for quick access to different features.

From the look of the video below, the Twins are now rock-solid and a lot easier to use. This project is loosely based on a recent panadapter project [Scott] undertook for the receiver side of the Twins.

#radiohacks #ad9850 #amateurradio #dds #directdigitalsynthesis #drake #ham #variablefrequencyoscillator #vfo