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DDS VFO Construction Manual – Issue 1

Page 1

DDS

VFO

C

ONSTRUCTION

M

ANUAL

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2
3
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Summary of Contents for DDS VFO

Page 1: ...DDS VFO Construction Manual Issue 1 Page 1 DDS VFO CONSTRUCTION MANUAL ...

Page 2: ...h is pre programmed and shipped in an anti static bag Do not remove the devices from their protective anti static bags until you have taken precautions against static discharge If possible use an anti static wrist strap and conductive mat These can be purchased readily from electronic retailers If these are not available then at least ensure you have discharged yourself by touching an earthed meta...

Page 3: ...5 3 Parts List 7 4 Construction 8 4 1 General 8 4 2 Construction Steps 8 5 Testing 11 6 Configuration 11 6 1 Understanding options 11 6 2 Procedure 12 7 Operation 13 8 Options 14 List of Figures Figure 1 Circuit diagram 6 Figure 2 Component overlay 10 Figure 3 Typical LCD operating display 13 ...

Page 4: ...ontrol 7 Displays power supply voltage 8 Programmable IF frequency Ensures the displayed frequency is the same as the transmitted frequency 9 Programmable IF offsets o Minus DDS output frequency is the IF frequency minus the displayed frequency o Plus DDS output frequency is the IF frequency plus the displayed frequency o Rev DDS output frequency is the displayed frequency minus the IF frequency o...

Page 5: ...ller has an internal analog to digital converter ADC which uses the 5 volt rail as a reference The ADC measures the incoming power supply rail via a resistive attenuator formed with R5 and R6 The calculated value is displayed on the LCD during use Two other inputs one analog A and the second digital D have been included in the PCB layout but are not implemented in the current software release The ...

Page 6: ...DDS VFO Construction Manual Issue 1 Page 6 Figure 1 Circuit diagram ...

Page 7: ...or R2 R4 R6 R7 R10 3 30K 1 4W 1 resistor R1 R3 R5 1 10K horizontal trimpot VR1 1 ATmega8 16PU 28pin DIP U1 1 AD9834BRUZ DDS 20 pin TSSOP U2 1 7805 5V regulator TO220 VREG1 1 50MHz crystal oscillator module half size XO1 1 16 x 2 LCD with backlight 80mm x 36mm Winstar WH1602B or equivalent LCD1 2 4 7uH moulded RF choke L1 L2 1 3 pin x 2 row 2 54mm pitch header HDR1 ISP 1 11mm Rotary Encoder BI Tech...

Page 8: ...der than non plated holes and makes it more difficult to remove components The lesson is to double check the values and orientation of components before installation There isn t a best scheme for loading the components however the suggested procedure is to load the smaller components first and then work upwards 4 2 CONSTRUCTION STEPS Refer to the parts list and Figure 2 when installing the compone...

Page 9: ...mounted on the reverse side with the short ends of the pins located in the PCB Ensure it is pushed in completely and solder the end pins first and check it is at right angle to the PCB before soldering the remaining pins Step 8 Rotary encoder The rotary encoder is mounted on the reverse side Insert into the holes and check that it is at right angle to the board before soldering It is not necessary...

Page 10: ...DDS VFO Construction Manual Issue 1 Page 10 Figure 2 Component overlay ...

Page 11: ...are version number This is then followed by the operating display As the DDS VFO has not been configured the LCD will display default settings These are Transmit frequency of 7 1MHz and a 1KHz Step The default IF frequency is 10MHz with a Minus offset so using an oscilloscope or a frequency counter verify that the DDS is outputting a 2 9MHz sine wave signal of around 300mV pk pk 6 CONFIGURATION 6 ...

Page 12: ...l toggle through the options Once completed press the encoder button for longer than 1 second and release 4 The IF frequency screen will be displayed and the cursor will be positioned on the 10MHz digit Rotating the encoder clockwise increments the digit while rotating the encoder anti clockwise decrements the digit Pressing the encoder button for less than 1 second will step the cursor onto the n...

Page 13: ...er push button for less than 1 second and release Each press cycles through the available steps which are 1KHz 100HZ and 10Hz Tuning Lock To lock the encoder from changing frequency press the encoder push button for more than 1 second A lock message will be displayed on the upper right of the LCD To unlock press the encoder push button for less than 1 second Voltage Display The power supply voltag...

Page 14: ...different value of current limiting resistor Check the LCD data sheet before applying power to determine the correct resistor value and change R9 if needed A non backlit display will also not be as deep and this needs to be taken into account when mounting to the front panel Additional inputs The PCB includes two additional inputs One is intended to measure an analog voltage and the other is confi...

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