VFO-003

Features

Software controlled VFO

• Arduino Pro Mini Microprocessor
  • 8-bit ATMEGA328 CPU
  • 8 MHz
  • 3.3V I/O
• Detachable Rotary Encoder/OLED card
  • SSD1306 OLED Display
    • I2C Interface
  • Rotary encoder
• Menu options
  • 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
• Si5351A Oscillator
  • 3 Outputs
  • 27 MHz TCXO crystal oscillator
  • I2C Interface
  • MS5351M Data Sheet - Alternate part for Si5351A
    • MS5351M Evaluation Report by QRP-Labs
• 3.3V, 50 Ohm outputs
  • +12.6 dBm output
• Power
  • MINI-360 DC/DC Buck regulator
  • 5-24 VDC
  • 30mA at 12VDC
• Fits in standard extruded enclosures

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

J7 - Arduino P5-P9

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

Measurements

• NanoVNA
• 10 Mhz signal from the VFO-003
• 1-100 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

Memory Usage

• 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);
}

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

Assembly Sheet / Parts List

VFO-003 Assembly Sheet - Rev 1