ozQRP CDV Instructions for use

CDV Construction Manual –Issue 3 Page 1
CDV
COMPACT DIGITAL VFO
CONSTRUCTION MANUAL

CDV Construction Manual –Issue 3 Page 2
CONTENTS
1Introduction..............................................................................................................................................................4
1.1 CDV features ........................................................................................................................................................................4
1.2 CDV specifications.............................................................................................................................................................5
2The Si5351A..............................................................................................................................................................6
3Circuit Description .................................................................................................................................................7
4Kit Supplied Parts ................................................................................................................................................ 11
5PCB Individual Parts List .................................................................................................................................. 11
6Construction........................................................................................................................................................... 12
6.1 General ................................................................................................................................................................................ 12
6.2 Steps ..................................................................................................................................................................................... 12
7Testing...................................................................................................................................................................... 16
7.1 General ................................................................................................................................................................................ 16
7.2 Power on............................................................................................................................................................................. 16
7.3 Controls............................................................................................................................................................................... 16
7.4 Output Signals .................................................................................................................................................................. 16
8Mounting to a panel............................................................................................................................................ 17
9Set-up........................................................................................................................................................................ 18
9.1 General ................................................................................................................................................................................ 18
9.2 Procedure........................................................................................................................................................................... 18
9.3 Understanding Menu options.................................................................................................................................... 18
9.4 Menu Option Ranges ..................................................................................................................................................... 21
10 Operation................................................................................................................................................................. 22
10.1 Operating Display........................................................................................................................................................... 22
10.2 Tuning.................................................................................................................................................................................. 22
10.3 Step selection.................................................................................................................................................................... 22
10.4 Scan mode.......................................................................................................................................................................... 23
10.5 RIT......................................................................................................................................................................................... 23
10.6 VFO Frequency calibration......................................................................................................................................... 24
10.7 Voltage display calibration......................................................................................................................................... 24
11 Using the CDV with a superhet rig................................................................................................................ 25
12 Optional Attenuator Low pass Filter Board.............................................................................................. 26
12.1 Schematic ........................................................................................................................................................................... 27
12.2 PCB Overlay....................................................................................................................................................................... 27
12.3 Construction...................................................................................................................................................................... 28
12.3.1 Soldering SMD devices .............................................................................................................................................................. 28
12.4 Attaching to the CDV ..................................................................................................................................................... 29
12.4.1 Direct.................................................................................................................................................................................................. 29
12.4.2 Wired.................................................................................................................................................................................................. 29

CDV Construction Manual –Issue 3 Page 3
List of Figures
Figure 1 Microcontroller and power supply schematic ...................................................................................8
Figure 2 Si5351A Clock generator schematic.......................................................................................................9
Figure 3 Display and controls schematic............................................................................................................. 10
Figure 4 Component overlay .................................................................................................................................... 12
Figure 5 OLED mounting............................................................................................................................................ 15
Figure 6 CDV panel cutting........................................................................................................................................ 17
Figure 7 CDV used in a superhet rig ...................................................................................................................... 25
Figure 8 Add-on board options................................................................................................................................ 26
Figure 9 Add-on board schematic........................................................................................................................... 27
Figure 10 Add-on board PCB overlay.................................................................................................................... 27
Figure 11 Attenuator filter board fitted to the CDV........................................................................................ 30
Change History
Date
Issue
Comments
30-Jan-2017
1
First release
10-Jan-2020
2
Added BFO fixed output feature. Added user programmable steps.
Improved frequency accuracy. Minor text changes.
1-Oct-2020
3
Rev. B PCB. 2 pin JST connector reversed, alternative 4 pin connector
wire colours.

CDV Construction Manual –Issue 3 Page 4
1INTRODUCTION
The CDV (Compact Digital VFO) is a variable frequency oscillator suitable for homebrew radio
transceivers and general signal generator applications. The CDV is built on a very small PCB that
holds all parts including the rotary encoder and OLED display.
The CDV can simultaneously generate two separate signal sources. The first output has a fixed
frequency while the second is a variable frequency source using a rotary encoder as the control.
The outputs are square wave but can be conditioned by an optional add-on attenuator/low-pass
filter board.
1.1 CDV FEATURES
Two simultaneous outputs. One variable frequency and one fixed frequency.
User programmable frequency steps.
BFO fixed output feature provides a replacement for a crystal in superhet rigs.
Simple and flexible configuration through on screen menus.
Clear and bright low current OLED display.
Very small overall size.
Simple control via a rotary encoder and two small pushbuttons.
Low power consumption.
Wide frequency range.
IF offset function.
Scanning function.
Receiver incremental Tuning (RIT).
RX/TX indication.
USB/LSB indication.
Power supply voltage display.
Automatic frequency adjustment when changing sidebands.
Calibration of frequency and voltage display.
Low power supply voltage warning.
Easy mounting using the rotary encoder shaft.
PCB comes with all SMD parts pre-loaded.
Assembly is quick and easy as most of the components are surface mount (SMD) and come pre-
installed on the PCB. There are only a handful of through-hole parts to install.
A kit of parts for the CDV including everything you need is available from www.ozQRP.com.

CDV Construction Manual –Issue 3 Page 5
1.2 CDV SPECIFICATIONS
1. PCB size: 52mm x 32mm.
2. Controls: Rotary encoder and 2 pushbuttons.
3. Display: 0.96 inch monochrome OLED.
4. Signal outputs: 1 x fixed frequency, 1 x variable frequency.
5. Fixed output frequency range: 100KHz to 100MHz.
6. Variable output frequency range: 100KHz to 100MHz.
7. Scan mode ranges: +-5KHz, +-50KHz of start frequency.
8. IF offset: VFO > IF, VFO < IF, NONE.
9. Receiver incremental Tuning (RIT) range: no limit.
10. Programmable frequency steps: Select from the range 1Hz, 10Hz, 100Hz, 1KHz, 5Khz,
10KHz, 25KHz and 100KHz.
11. Operating supply voltage range: 5 to 15V DC.
12. Average operating current: 35mA.
13. TX/RX and USB/LSB logic inputs. An input larger than 3.3V is logic high.
14. Low power supply alarm: 5 to 15V DC.
15. Output impedance: 50 Ohms.
16. Output drive level: over 3V pk-pk Hi Z. 2V pk-pk 50 ohms.
17. Output coupling: series capacitor (100nF).
18. Reverse polarity protection: series diode.
19. Input Output connectors: JST 2mm pin pitch polarised connectors.

CDV Construction Manual –Issue 3 Page 6
2THE SI5351A
The heart of the CDV is the Si5351A-B-GT clock generator from Silicon Labs. This amazing
device includes two programmable Phase Locked Loops (PLL), a matrix switch, and three
programmable fractional dividers. The PLLs obtain a reference frequency from an external
25MHz crystal to generate an intermediate high frequency clock between 600MHz and 900MHz.
The PLL outputs are directed by the matrix switch to the respective fractional divider where the
PLL frequency is divided down to provide the desired output frequency. The PLL and fractional
dividers are controlled by a microcontroller via an I2C interface. Through a combination of
programmable PLL frequencies and fractional divider values the clock generator is capable of
outputting frequencies from a few KHz up to 200MHz with high accuracy and fine resolution.
The CDV uses two PLL and two fractional dividers to provide a fixed output and a variable
output. The third output is unused.

CDV Construction Manual –Issue 3 Page 7
3CIRCUIT DESCRIPTION
Integrated circuit U2 is a Si5351A clock generator chip. A 25MHz crystal supplies the master
clock on pins 2 and 3. The Si5351A is controlled over a shared I2C bus by microcontroller U1.
The 3.3V power supply rail is applied to pins 1 and 7. Capacitors C8 andC12 and a ferrite bead
help guard against instability and decouple the IC from the power supply. The variable output
(VFO) appears on pin 10 and is capacitively coupled by C5 to the VFO output connector.
Similarly the fixed frequency output on pin 9 is capacitively coupled by C11 to the FIX output
connector.
The output signals from the Si5351A are square wave in shape with a frequency spectrum being
almost entirely comprised of odd harmonics. While this is adequate for most situations, an
external add-on attenuator filter board is available for more demanding applications. See
section 11 for more details.
The microcontroller is an Atmel ATmega328 and runs an internal 8MHz clock which avoids the
need for an external crystal. It controls the OLED and Si5351A over a common I2C bus on pins
28 and 27. The I2C standard calls for bus pull-up resistors and this is achieved through two 4.7K
resistors R7 and R8.
A rotary encoder produces quadrature signals when rotated and one line (REA) is fed into the
microcontroller interrupt input (pin 32) and becomes the reference input. Once an interrupt is
detected the state of the other line (REB) is read and the direction determined. The rotary
encoder also incorporates a press button switch input on U1 pin 1 and is used for a number of
functions as described later. U1 incorporates pull-up resistors for the encoder inputs so they are
normally held high and capacitors C9 and C10 help limit encoder switch bounce.
The CDV uses a small 0.96 inch monochrome 128 x 64 pixel matrix OLED for display. If
characters were written unmodified to the matrix they would be small and difficult to read, so
the firmware combines pixels to write larger characters with 4 rows of 10 characters. The OLED
does not require a backlight and has excellent brightness and contrast in high ambient light
levels. It is also controlled through the common I2C bus.
The microcontroller has an internal analog to digital converter (ADC) which measures the
incoming power supply rail via a resistive attenuator formed with R3 and R4. The calculated
value is displayed on the OLED during use.
The microcontroller monitors the state of the TX/RX input on pin 31, while the state of the
USB/LSB input is monitored on pin 30. The inputs are attenuated by 22K resistors and the
microcontroller inputs are further protected by 3.3V Zener diodes. The inputs are considered
low when the input is below about 3.3V. An input above 3.3V is considered a high. The inputs
can handle up to 20V levels.
The incoming power supply is regulated to 3.3V by a 78L33 100mA regulator which has its tab
soldered to the PCB groundplane to act as a heatsink. The 3.3V rail powers the microcontroller,
Si5351A and the OLED. Diode D1 provides reverse polarity protection. When the power supply
is connected in reverse, the diode will not conduct and the main circuits will be protected.
The PCB also includes space to fit an ISP connector to allow future software upgrades.

CDV Construction Manual –Issue 3 Page 8
Figure 1 Microcontroller and power supply schematic

CDV Construction Manual –Issue 3 Page 9
Figure 2 Si5351A Clock generator schematic

CDV Construction Manual –Issue 3 Page 10
Figure 3 Display and controls schematic