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

CDV Construction Manual –Issue 3 Page 11
4KIT SUPPLIED PARTS
QTY
Item
Description
1
CDV PCB
PCB. All SMD parts installed.
1
OLED
0.96 inch OLED display. I2C control
1
Rotary encoder
Rotary encoder. 6mm D style shaft
1
15mm knob
Rotary encoder knob
2
Tactile pushbutton
PCB mount through hole momentary pushbutton
2
Pushbutton caps
Pushbutton actuators
1
4 pin connector
Power and control connector
2
2 pin connector
Signal output connector
1
4 wire cable
Colour coded power/control cable
2
2 wire cable
Colour coded signal output cable
5PCB INDIVIDUAL PARTS LIST
Desig.
Value
Type
C1
1uF
Capacitor ceramic MLCC SMD 0603
C2
100nF
Capacitor ceramic MLCC SMD 0603
C3
100nF
Capacitor ceramic MLCC SMD 0603
C4
100nF
Capacitor ceramic MLCC SMD 0603
C5
100nF
Capacitor ceramic MLCC SMD 0603
C6
100nF
Capacitor ceramic MLCC SMD 0603
C7
100nF
Capacitor ceramic MLCC SMD 0603
C8
100nF
Capacitor ceramic MLCC SMD 0603
C9
10nF
Capacitor ceramic MLCC SMD 0603
C10
10nF
Capacitor ceramic MLCC SMD 0603
C11
100nF
Capacitor ceramic MLCC SMD 0603
C12
100nF
Capacitor ceramic MLCC SMD 0603
R1
22K
Resistor 1% SMD 0603
R2
22K
Resistor 1% SMD 0603
R3
22K
Resistor 1% SMD 0603
R4
1K
Resistor 1% SMD 0603
R5
22K
Resistor 1% SMD 0603
R6
22K
Resistor 1% SMD 0603
R7
4.7K
Resistor 1% SMD 0603
R8
4.7K
Resistor 1% SMD 0603
R9
4.7K
Resistor 1% SMD 0603
D1
1N4148
Diode SMD SOD123
ZD1
3V3
Zener diode 3.3V 500mW SMD SOD123
ZD2
3V3
Zener diode 3.3V 500mW SMD SOD123
REG1
78L33
Voltage regulator 3.3V 100mA SMD SOT89-3
U1
ATmega328P
Atmel 32K 8 bit microcontroller
U2
Si5351A-B-GT
Clock generator
X1
25MHz
Crystal 25MHz SMD
FB1
-
Ferrite Bead SMD
OLED1
-
0.96 inch 128 x 64 monochrome OLED
RE1
-
Through hole rotary encoder with switch
PB1
-
PCB mount through hole tactile momentary action switch
PB2
-
PCB mount through hole tactile momentary action switch
VFO
-
2 pin JST 2mm pitch male shrouded header
FIX
-
2 pin JST 2mm pitch male shrouded header
PWR
-
4 pin JST 2mm pitch male shrouded header
ISP
-
not installed

CDV Construction Manual –Issue 3 Page 12
6CONSTRUCTION
6.1 GENERAL
The CDV is built on a high quality fibreglass PCB. The PCB is doubled sided with tracks on both
sides but with the top side mainly forming a ground plane.
Components are loaded into the PCB from both sides. When the component side is mentioned in
the following instructions it refers to the side of the PCB where the SMD parts are installed. The
reverse side is referred to as the solder side.
To assist construction the PCB has a screen printed component overlay and a solder mask to
help guard against solder bridges.
The components are static sensitive. Use anti-static measures when handling the
PCB out of its protective bag.
6.2 STEPS
Step 1: PCB
Remove the PCB from its protective bag. Check for damage during shipping. The PCB comes
shipped with all SMD devices pre-installed.
Figure 4 Component overlay

CDV Construction Manual –Issue 3 Page 13
Step 2: Power Connector
Insert the 4 pin JST connector into the component side of the PCB. The side of the connector
with the cutout faces the encoder. Hold firmly against the PCB and solder in place.
Step 3: Output Connectors
If the CDV is to be used with an optional add-on attenuator filter board, decide if it is
to be soldered directly to the PCB. If being soldered directly the connector can be
omitted.
Insert the two 2 pin JST connectors into the component side of the PCB.
For Rev. A PCB the side of the connector with the cutout faces towards the top of the PCB. If the
PCB is Rev. B the side of the connector with the cutout faces towards the bottom of the PCB.
Hold firmly against the PCB and solder in place.

CDV Construction Manual –Issue 3 Page 14
Step 4: Pushbuttons
Insert the pushbuttons into the solder side of the PCB. It may be necessary to straighten the pins
slightly so they fit easily. Ensure they sit flat and at right angles to the PCB, then solder in place.
Step 5: Rotary Encoder
Insert the rotary encoder into the solder side of the PCB. Ensure it sits flat and at right angles to
the PCB then solder in place.

CDV Construction Manual –Issue 3 Page 15
Step 6: OLED
The OLED is inserted into the solder side of the PCB using the integral 4 pin male header.
Position the OLED so that its front face sits just behind the rear of the panel where the CDV is
mounted. See Figure 5.
Solder one pin and double check the clearance and ensure that the OLED is parallel to the PCB. If
necessary melt the solder and reposition, then solder the remaining pins.
It may also be necessary to trim the top of the header pins if a metal panel is used to avoid the
possibility of short circuits.
If the OLED is installed close to the main PCB, it may be necessary to trim the pins on the 2pin
JST connectors to avoid them touching the back of the OLED.
Figure 5 OLED mounting
Step 7: Knobs and caps
Push the small long actuator knobs onto the pushbuttons. Take care to avoid excessive sideways
force that could damage the switch.
The encoder knob slides onto the ‘D’ style encoder shaft. A small amount of lubrication, such as
Silicone spray, makes it easier to slide on and off.
The knob must be removed from the shaft before mounting the CDV to a panel.

CDV Construction Manual –Issue 3 Page 16
7TESTING
7.1 GENERAL
The CDV microcontroller has been programmed and the board given a functional check before
being dispatched. This means the CDV should work first time, however the following procedure
provides a quick check that the CDV is operating correctly once assembled.
If there are problems look for errors with the soldering of the connectors, controls and OLED. If
there is no sign of life check that the power supply is connected with the correct polarity. No
damage should result as the CDV has reverse polarity protection.
7.2 POWER ON
1. Connect the 4 pin connector red wire to the power supply positive lead. Connect the
black wire to the power supply negative lead. The power supply can be between 5 and
15V DC.
2. Turn on the supply and note the current. It should be around 30mA. If it’s far from this
turn off immediately and look for problems.
3. The OLED should display the opening banner along with the firmware version number,
then after a short period display the operating screen.
7.3 CONTROLS
1. Rotate the encoder knob and check that the frequency can be changed up and down.
2. Press the SCAN button and check that Scan mode menu appears, and select Exit with the
STEP button to return to the operating screen.
3. Press the STEP button and check that the frequency step can be changed.
4. Press and hold the encoder button for a few seconds and check that the Set-up screen is
displayed. Select FULL with the STEP button and step through the menus using the
SCAN button and return to the operating screen.
5. Connect the 4 pin connector white (blue) wire to the power supply positive lead. The
RX/TX display should change state.
6. Connect the 4 pin connector yellow (grey) wire to the power supply positive lead. The
USB/LSB display should change state.
7.4 OUTPUT SIGNALS
1. Terminate the outputs with a 50 ohms resistor (two 100 ohm in parallel) and place an
oscilloscope across the load. Verify a square wave output signal with an amplitude of
around 2V pk-pk at the expected frequency.
The fixed output is disabled by default so it needs to be enabled in Set-up to view its
output.
If an optional add-on board is installed, then the output will be conditioned. The
amplitude depends on the attenuator fitted and the waveform will be closer to a
sine wave.

CDV Construction Manual –Issue 3 Page 17
8MOUNTING TO A PANEL
The CDV is small and light and can be mounted to a panel simply by using nothing more than the
rotary encoder shaft.
Before mounting a rectangular cutout and 4 holes need to be made to the panel as shown in
Figure 6.
Once the cutout and the holes are complete insert the CDV from the rear of the panel then place
the nut and washer on the shaft. Check that the display lines up with the cutout and the
pushbuttons are free to operate in their holes and tighten the nut.
Figure 6 CDV panel cutting

CDV Construction Manual –Issue 3 Page 18
9SET-UP
9.1 GENERAL
The CDV has a comprehensive range of programmable parameters which allow the CDV to be
used in a number of varied operating conditions.
To provide for easy and faster operation the Set-up menus are divided into three levels:
a. QUICK –this level only includes the common main menus.
b. MISC –this level is used to set the miscellaneous functions.
c. FULL –all Set-up menus are available.
9.2 PROCEDURE
1. To enter Set-up mode, press and hold the encoder switch down for 2 seconds until the
display shows CDV SETUP and then release.
2. Press the STEP button to select the Set-up level and then confirm with the SCAN button.
3. The menus are sequentially accessed by pressing the SCAN button.
a. Menu items that have multiple fixed values (e.g. YES/NO, +/-) are selected by
pressing the STEP button.
b. Menu options that have numerical values (e.g. frequency) are incremented and
decremented using the rotary encoder.
c. Menus displaying frequency use the STEP button to step the cursor through the
digits.
4. Once the last menu is completed the Set-up procedure is exited and any new values
stored in non-volatile memory. These are loaded again at power on.
The menus and their current values can be displayed anytime without alteration by
progressing through the menus using only the SCAN button.
9.3 UNDERSTANDING MENU OPTIONS
Fixed O/P
The variable output is always enabled. The Fixed output can be enabled or disabled if not
required with this option. The Fixed output has three options:
1. NO –the output is disabled.
2. YES –the output is enabled and the frequency is manually entered.
3. BFO –the output is enabled. The frequency is set to IF low or IF high depending on the
state of the USB/LSB input and the VFO mixing scheme.
Fixed Freq
This option allows the setting of the fixed output frequency, and is only available if the Fixed
O/P is set to YES.

CDV Construction Manual –Issue 3 Page 19
IF Offset
This option is set when the CDV is used as a local oscillator in a Superhet rig. The OLED will
display the receive/transmit frequency while the actual VFO signal frequency will be offset by
an amount equal to the difference between the IF and TX frequencies.
To accommodate a wide range of applications there are two offset options available.
a) VFO > IF. This places the VFO frequency above the IF frequency and is the most
commonly used option.
The VFO frequency is calculated in firmware using the following equation:
VFO frequency = IF frequency + TX frequency.
80M example. 13.5MHz = 10MHz + 3.5MHz.
20M example. 24MHz = 10MHz + 14MHz.
b) VFO < IF. This places the VFO frequency below the IF frequency and is most suitable
when the TX frequency is below the IF frequency.
The VFO frequency is calculated in firmware using the following equations:
If TX frequency < IF frequency, then VFO frequency = IF frequency - TX frequency.
80M example. 6.5MHz = 10MHz - 3.5MHz.
If TX frequency > IF frequency, then VFO frequency = TX frequency - IF frequency.
20M example. 4MHz = 14MHz - 10MHz.
An IF Offset of NONE means the VFO output frequency will be the same as the displayed
frequency. This is the setting selected when the VFO is to be used as a general purpose signal
generator or with a Direct Conversion receiver.
Depending on the transceiver mixing arrangement there may be a sideband
inversion if the offset is VFO > IF.
For example, LSB generated in the balanced modulator would actually be USB at the
transmitter output, and vice versa.
If this is the case, the display can be corrected using the Set-up SIDEBAND option.

CDV Construction Manual –Issue 3 Page 20
IF Freq High and IF Freq Low
Two separate IF frequencies (IF HI Freq and IF LO Freq) are included to allow the VFO firmware
to correct the output frequency when sidebands are changed. To generate the opposite
sideband it is necessary to shift the carrier oscillator frequency from one side of the filter
passband to the other. Without this adjustment the transmitted frequency would not accurately
reflect the displayed frequency.
If it is required that the carrier oscillator does not change frequency when the sideband is
changed, then simply make both IF HI Freq and IF LO Freq the same.
If the IF Offset option is set to NONE the IF Freq menus are not displayed.
TX Freq
This option allows the initial operating frequency to be set.
The TX Freq value in conjunction with the IF Offset and IF Freq is used by the firmware to
calculate the actual VFO frequency.
When the IF Offset option is set to NONE the VFO displayed frequency is the same as the
transmit frequency.
Steps
The option allows the selection of steps. The step value is the amount the frequency is changed
as the rotary encoder moves one position. When this option is reached the current steps will be
displayed. If no changes are required simply press the SCAN button to go to the next option.
To change the steps do the following:
1. Press the rotary encoder switch down briefly to clear and reset the current steps.
2. Rotate the rotary encoder to display the required step in the top line.
3. Press the STEP button to select the step. This is then displayed in the bottom screen.
4. Repeat steps 2 and 3 to add extra steps.
5. When finished press the SCAN button to go to the next option.
30S Freq Save
This option enables automatic saving of the current frequency and step in EEPROM so that it is
recalled the next time the VFO is powered on. The EEPROM has a maximum specification of
100,000 write/erase cycles, so to protect it from excessive writes, the save is performed only
once per frequency change and only after a 30 second idle period has elapsed. If the encoder is
operated so that there is less than 30 seconds between changes no saves will be performed.