DDS AD9910 V3 Arduino Shield Signal Generator 600 [email protected] AM FM Sweep, HAM LO, S-Curve, Low Spurs
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Hello! In this video, I will introduce the new, improved version 3.5 of our AD9910-based DDS shield for Arduino. Here are the key enhancements:
1. Now let’s discuss each innovation in more detail:
In the old version 2, three buttons were used for control and navigation through the menu , while in the new version, they have been replaced with a convenient encoder that allows for quick adjustments of parameters across a wide range of values.
2. Another modification was the addition of a dedicated button for quickly enabling or disabling the signal on the RF OUT output. The current output status is displayed in two locations: on the OLED display and by an LED located above the RF OUT SMA connector. The illuminated LED indicates that the output is active.
3. LEDs have also been added next to the other SMA connectors. An illuminated LED indicates the active state of the corresponding SMA connector. The LED above the REF CLK IN connector lights up when one of the external clock sources is selected in the clock settings, signaling that an external generator should be connected to this input.
The PLL Lock LED lights up when the internal PLL module is active and the frequency lock has been successfully achieved.
This is a sign that the clock settings are correctly configured.
This LED can also be useful when experimenting with overclocking the DDS core.
Lastly, the LED above the TRG OUT connector indicates that this output is active and pulses are being sent for synchronization with an oscilloscope.
4. We have adapted the new board to support larger OLED screens—1.54 inches. For comparison, this is how the screen for DDS version 2 looked. We have also maintained compatibility with the older smaller 0.96-inch displays. The larger screen significantly simplifies working with the DDS for people with impaired vision.
5a. Now, when switching the clock source, there is no longer a need to resolder capacitors, as was required in version 2. Thanks to the RF switch, you can instantly switch between the built-in TCXO and an external clock source. For example, let's connect an external OCXO from Wenzel with a frequency of 50 MHz. As you can see, the DDS output frequency exactly matches the one set in the settings.
Now, let's go into the clock settings and select the external TCXO/OCXO as the source. In this mode, the built-in PLL will be activated. Currently, the DDS output frequency no longer matches the set frequency because the TCXO on the board operates at 40 MHz, while we switched the DDS to an external generator operating at 50 MHz. To correct this discrepancy, we need to properly set the external source frequency and save the settings. Now everything is correct, and the DDS output frequency once again matches the one set in the settings.
5.1 To clock the DDS directly, meaning with the internal PLL disabled, there is also no need to resolder any components; this can be done through the settings menu. We will demonstrate the operation of this mode using an external low-noise generator, the RCLN1000, with an output frequency of 1 GHz.
6. The new version has introduced a LOCAL oscillator mode. This mode will be particularly appreciated by HAM radio enthusiasts, as the DDS is an ideal solution for use as a local oscillator in superheterodyne radio receivers due to its very low phase noise and high frequency stability. A separate operating mode was created to eliminate the need to recalculate the output frequency each time; instead, you can simply set the intermediate frequency and the tuning step. In the settings, you can choose to either add or subtract the intermediate frequency from the carrier frequency.
7. Another new mode that HAM radio enthusiasts will appreciate is the S-Curve mode. This mode is essential for optimal tuning of a quadrature coil or for testing a ceramic discriminator in an FM detector. To use this mode, you need to connect the RF output to the receiver input through a 70 dB attenuator. Then, connect the receiver output to the first channel of the oscilloscope. It is recommended to capture the signal before the output filter. Additionally, connect the TRG output to the second channel of the oscilloscope and set the trigger to capture the rising edge on this channel.
8. Another new feature is the protection against overvoltage or undervoltage. If the supply voltage deviates from the recommended value of 7.5 volts, the protection is triggered, disconnecting the AD9910 and displaying a warning message on the screen. The disconnection will occur if the supply voltage drops below 4 volts or exceeds 8 volts.