VFO-003

Features

Software controlled Variable Frequency Oscillator (VFO)

• Arduino Pro Mini Microprocessor
  • 8-bit ATMEGA328 CPU
  • 8 MHz
  • 3.3V
  • 30KB of Flash Memory (32KB - 2KB bootloader)
  • 2KB of SRAM
  • EEPROM
  • Program Flash over FTDI connection
• Detachable Rotary Encoder/OLED card
  • SSD1306 OLED Display
    • I2C Interface
    • 128x32 or 128x64
    • Pins must be GND/VCC/SCL/SDA
    • Run at 3.3V
  • Rotary encoder with pushbutton
• Si5351A Frequency Generator
  • 3 Outputs
  • 3.3V, 50 Ohm outputs
  • +12.6 dBm output
  • 27 MHz TCXO crystal oscillator
    • 2.5 PPM
  • I2C Interface
  • MS5351M Data Sheet - Alternate part for Si5351A
    • MS5351M Evaluation Report by QRP-Labs
• Menu options - Minimal Viable Product
  • Select between 3 VFOs
  • Adjust frequency
  • Step sizes: 1Hz, 10 Hz, 100 Hz, 1 KHz, 10 KHz, 100 KHz, 1 MHz, 10 MHz steps (software controllable)
  • Adjust frequency accuracy to 0.01 Hz precision
  • Turn VFO Off/On (Off = 3.3V)
  • Save default values which are loaded at power up
• Power
  • MINI-360 DC/DC Buck regulator
  • 5-23 VDC
  • 30mA at 12VDC
  • High efficiency
  • Jumper to remove Power into card - protects 3.3V devices while adjusting the output voltage
• Fits in standard extruded enclosure
  • Aluminum Project Box Enclosure DIY 100*76*35mm

Arduino Pro Mini

• Ebay search for Arduino Pro Mini 3.3V
• Amazon search for Arduino Pro Mini 3.3V

Power

• 5-24 VDC
• 30mA at 12VDC
• 55mA at 5V
• 35mA at 9V
• 28mA at 14V
• 33mA at 23V

TCXO

• TXCO requires very little frequency correction
• 27 MHz TCXO crystal oscillator
  • Package / Case: 5 mm x 3.2 mm
  • Frequency: 27 MHz
  • Frequency Stability: 2.5 PPM
  • Supply Voltage - Max: 3.3 V
• 25 MHz - Alternate would require software changes

Connectors

J1 - OLED

• Located on display/encoder board

1. SDA
2. SCL
3. Vcc
4. GND

J2 - Display Encoder/OLED (Display card)

• Connect via cable to display/encoder board

1. Encoder A
2. Encoder B
3. Encoder Switch
4. SCL
5. SDA
6. Vcc
7. GND

J3 - Display Encoder/OLED (Main card)

• Connect via cable to display/encoder board

1. Encoder A
2. Encoder B
3. Encoder Switch
4. SCL
5. SDA
6. Vcc
7. GND

J4 - FTDI

• Can install 1x6 header on the Arduino Pro Mini and not install this

1. GND
2. GND
3. Vcc
4. RX
5. Tx
6. DTR

J5 - Arduino A0-A3/C10-D13

1. A3
2. A2
3. A0
4. D13
5. D12
6. D11
7. D10
8. Vcc (not connected on Rev 1 PCB)
9. GND (not connected on Rev 1 PCB)

J6 - Disconnect for Mini-360 Power Supply

• The Mini360 Buck Converter comes adjusted for a very high output voltage
• Remove jumper to adjust the output voltage to 3.3V without powering the rest of the card
• Install to power the card from the power supply only after adjusting output

J7 - Output disconnects

• Cut rear side trace to disconnect
• Can be used to install external LP filters
• Limited use due to 74AC14 drivers

J8 - Arduino P5-P9

1. P5
2. P6
3. P7
4. P8
5. P9
6. Vcc
7. GND

J9-J11 - SMA

• SMA or BNC

J12 - I2C (Rev 3)

P1-P3 - Outputs (BNCs)

• SMA or BNC

Output Power - Power Calculation

RMS Voltage of square wave

• Square Wave Calculator
• 2.33V^2/100 = 0.0542W
• Power is split between Source and load resistors
• 0.02714W

dBm Calculation

• mW to dBm calculator

• Expect 14.3 dBm drive
• Measured 12.6 dBm with NanoVNA - Pretty close
• 3 dB attenuator to reduce for Level 7 mixers (like the ADE-1 mixer)

Measurements

• NanoVNA
• 10 Mhz signal from the VFO-003
• 1-350 MHz

1-350 MHz scan

Harmonic content

• 10MHz fundamental = +12.25 dBm
• 20MHz harmonic = -16.75 dBm
• 30MHz harmonic = +2.4 dBm
• 50MHz harmonic = -2.1 dBm

Schematic

• Rev 3 schematic

Software

• GitHub Repository
• Minimal Viable Product build - GitHub repo

VFO Menu

• Set Step Size
  • 1Hz, 10 Hz, 100 Hz, 1KHz, 10KHz, 100 KHz, 1 MHz, 10 MHz
• Set frequency
  • 10 KHz to 40 MHz in step size steps
• Select VFO
  • VFO0, VFO1, VFO2
• VFO On/Off
  • On, Off
• Set Calibration Value
  • In step size steps (in 0.01 Hz steps)
• Save (power-on) defaults

Memory Usage

• Minimal Viable Product Build - GitHub repo branch
• Arduino bootloader 2048 of Flash
• Display code: 10260 of Flash and 1033 of SRAM using u8g2
• Alternate display code: 6198 of Flash and 446 of SRAM using u8x8
• Si5351 code: 12076 of Flash and 378 of SRAM

Total Memory usage with u8g2 Library

Sketch uses 25970 bytes (84%) of program storage space. Maximum is 30720 bytes. Global variables use 1503 bytes (73%) of dynamic memory, leaving 545 bytes for local variables. Maximum is 2048 bytes.

Total Memory usage with u8x8 Library

• ~4K less than the u2g2 library

Sketch uses 22064 bytes (71% of program storage space. Maximum is 30720 bytes. Global variables use 925 bytes (45%) of dynamic memory, leaving 1142 bytes for local variables. Maximum is 2048 bytes.

Minimal u8g2 code

• Minimal u8g2Test code
• olikraus u8g2 Library

Sketch uses 10260 bytes (33%) of program storage space. Maximum is 30720 bytes. Global variables use 1033 bytes (50%) of dynamic memory, leaving 1015 bytes for local variables. Maximum is 2048 bytes.

• Code

void setup(void)
{
  u8g2.begin();

}

void loop(void)
{
  printStringToOLED("VFO-003");
}

void printStringToOLED(char * charStr)
{
  u8g2.clearBuffer();
  u8g2_prepare();
  u8g2.drawStr( 0, 0, charStr);
  u8g2.sendBuffer();
}

// u8g2_prepare()
// Setup the screen font, etc
// List of fonts
// https://github.com/olikraus/u8g2/wiki/fntlist8#u8g2-fonts-capital-a-height-38
void u8g2_prepare(void)
{
  u8g2.setFont(u8g2_font_t0_11b_tf); // 8 Pixel tall font
  u8g2.setFontRefHeightExtendedText();
  u8g2.setDrawColor(1);
  u8g2.setFontPosTop();
  u8g2.setFontDirection(0);
}

Minimal u8x8 code

• Minimal U8X8Test code
• u8x8 olikraus Library
• u8x8 Reference Guide

Sketch uses 6198 bytes (20%) of program storage space. Maximum is 30720 bytes. Global variables use 446 bytes (21%) of dynamic memory, leaving 1602 bytes for local variables. Maximum is 2048 bytes.

• Code

// https://github.com/olikraus/u8g2/wiki/u8x8reference#c-example

#include <Arduino.h>
#include <SPI.h>
#include <U8x8lib.h>

#define U8X8_HAVE_HW_I2C

U8X8_SSD1306_128X32_UNIVISION_HW_I2C u8x8(U8X8_PIN_NONE);

void setup() {
  // put your setup code here, to run once:
  u8x8.begin();
}

void loop() {
  // put your main code here, to run repeatedly:
  u8x8.setFont(u8x8_font_victoriabold8_r);
  u8x8.drawString(0,0,"Hello World!");
  delay(1000);

}

I2C 16x2 LCD Minimal code

• Hello World code
  • Much smaller code size than OLED code

Sketch uses 3080 bytes (10%) of program storage space. Maximum is 30720 bytes. Global variables use 263 bytes (12%) of dynamic memory, leaving 1785 bytes for local variables. Maximum is 2048 bytes.

Minimal Si5351 code

• Test code
• Si5351 Etherkit Library

Sketch uses 12072 bytes (39%) of program storage space. Maximum is 30720 bytes. Global variables use 378 bytes (18%) of dynamic memory, leaving 1670 bytes for local variables. Maximum is 2048 bytes.

#include <Arduino.h>
#include "si5351.h"

// Constructors
Si5351 si5351;
// End of constructor list

void setup(void)
{
  unsigned long VFO_0_Freq;
  unsigned long VFO_1_Freq;
  unsigned long VFO_2_Freq;
  bool i2c_found;
  VFO_0_Freq = 14000000;
  VFO_0_Freq = 14000000;
  VFO_0_Freq = 14000000;
  // Si8351 initialiation
  si5351.init(SI5351_CRYSTAL_LOAD_6PF, 27000000, 0);
  si5351.set_freq(VFO_0_Freq, SI5351_CLK0);
  si5351.set_freq(VFO_1_Freq, SI5351_CLK1);
  si5351.set_freq(VFO_2_Freq, SI5351_CLK2);
  si5351.update_status();  
  si5351.set_correction(0, SI5351_PLL_INPUT_XO);
  si5351.drive_strength(SI5351_CLK0,SI5351_DRIVE_8MA);
  si5351.drive_strength(SI5351_CLK1,SI5351_DRIVE_8MA);
  si5351.drive_strength(SI5351_CLK2,SI5351_DRIVE_8MA);
}

void loop(void)
{
}

Rotary Encoder

• Best code
  • Glitch free due to state machine
    • Test by going to top or bottom of the rotation and trying to go past end
  • Fast rotation rate
    • No delay loops for deglitching

Feature Adds

• CAT control
• Pase control for the Si5351 - Generate IQ clocks 90 deg out of phase

Mechanicals/Enclosure

• Detachable Front Panel OLED with Rotary Encoder

• Designed to fit into Aluminum Project Box Enclosure DIY 100*76*35mm - ebay search

Rev 1 Board Issues List

No major issues

• J5-9 and J5-10 are missing connections
  • Add wires on reverse side of the PCB if needed
• Note orientation of I2C termination resistors
  • Installed sideways by accident on first build

• Note orientation of Mini360
  • Put on backwards on first build
  • Always use a current limited power supply (I did, no damage)
  • Always adjust Mini360 with 3.3V SEL jumper removed
  • Solder in with short leads - space up a bit to allow rework
  • Orientation is with inductor towards edge of card

Rev 3 Design

• Adds J12, I2C connector
  • Use with I2C Peripheral like port expanders

• Add silkscreen, "VADJ>" pointing to the adjustment pot on Mini360

• Add breakaways for Front Panel to make it easier to separate

• Switch to 0.1" pitch SMA edge launch connectors

• Add ferrite bead and cap to power display board
• Add P2-P4 to J8
  • Easier to tap into encoder lines (after filter)
• Add J13-J15 to break connections between drivers and BNC connectors
  • Cut jumper on rear side of card if needed

Assembly Sheet / Parts List

VFO-003 Assembly Sheet - Rev 1