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

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

SDA
SCL
Vcc
GND

J2 - Display Encoder/OLED (Display card)

Connect via cable to display/encoder board

Encoder A
Encoder B
Encoder Switch
SCL
SDA
Vcc
GND

J3 - Display Encoder/OLED (Main card)

Connect via cable to display/encoder board

Encoder A
Encoder B
Encoder Switch
SCL
SDA
Vcc
GND

J4 - FTDI

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

GND
GND
Vcc
RX
Tx
DTR

J5 - Arduino A0-A3/C10-D13

A3
A2
A0
D13
D12
D11
D10
Vcc (not connected on Rev 1 PCB)
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

P5
P6
P7
P8
P9
Vcc
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

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

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

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

VFO-003

Contents

Features

Arduino Pro Mini

Power

TCXO

Connectors

J1 - OLED

J2 - Display Encoder/OLED (Display card)

J3 - Display Encoder/OLED (Main card)

J4 - FTDI

J5 - Arduino A0-A3/C10-D13

J6 - Disconnect for Mini-360 Power Supply

J7 - Output disconnects

J8 - Arduino P5-P9

J9-J11 - SMA

J12 - I2C (Rev 3)

P1-P3 - Outputs (BNCs)

Output Power - Power Calculation

RMS Voltage of square wave

dBm Calculation

Measurements

1-350 MHz scan

Harmonic content

Schematic

Software

VFO Menu

Memory Usage

Total Memory usage with u8g2 Library

Total Memory usage with u8x8 Library

Minimal u8g2 code

Minimal u8x8 code

I2C 16x2 LCD Minimal code

Minimal Si5351 code

Rotary Encoder

Feature Adds

Mechanicals/Enclosure

Rev 1 Board Issues List

Rev 3 Design

Assembly Sheet / Parts List

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