Raspberry Pi Pico Based VFO for Expanding Vintage C.B. Radios

I built a DDS VFO from a raspberry pi pico, a si5351 clock generator and an ssd1306 OLED display.

A DDS VFO is a direct digital synthesis variable frequency oscillator.

This project can be used to expand an antique 23 channel C.B. radio to allow operation on the full 40 channel citizens band. There are other DDS VFOs based on arduino boards, but this one is unique in that it uses the raspberry pi pico, and the code has practical examples of using multi core programing, and multiple IIc ports simultaneously. The source code is an Arduino sketch so it is very accessible for even the novice tinkerer.

The parts list consists of 1 raspberry pi pico.

1 si5351 clock generator

1 ssd1306 display

2 momentary push buttons for channel and menu navigation

1 7805 voltage regulator

2 small filter caps of 25 volt value 1 at .33 uf and one at .1 uf

1 or 2 perf boards depending on how you choose to organize the components

1 project box

some 50 ohm coaxial cable

and project wire.

The tools needed are a soldering iron

A screwdriver for opening the radio.

A frequency counter for testing the si5351 and calibrating it once it is installed on the C.B. Radio.

Wire the components together as shown in the diagram, it is best to use a breadboard while testing to ensure everything works. I had a bad oled display that was brand new. You can run both the SI5351 and the ssd1306 off of the same IIc buss if you prefer, but you will have to modify the code.

This is easy to do with a port scanner. I wrote a dual IIc port scanner which you can find in the iic support zip file on my website www.circuitsecrets.com After wiring the components together upload the port scanner sketch to the raspberry pi pico.

Substitute the address of your oled module into the next example sketch in the I2C zip file from circuitsecrets.com Upload the sketch to the raspberry pi pico and confirm the display is working as intended.

Use the final sketch in the i2c zip file and the frequency counter to test the si5351 as shown in this video.

The sketch can be found on circuitsecrets.com

To understand how the sketch works check out the following videos.

Add the voltage regulator and switches and assemble the VFO.

I chose to put the regulator and filter caps on a separate board inside the C.B. radio.

Check out the video for the installation in a Cobra 21, many older C.B. radios are similar.