LockFreq

A frequency lock wrapper class to the AD9954 DDS controller. Will update the DDS frequency to follow a voltage on one of the analog input pins.

Getting started

You'll need to include the DDS and SPI classes, along with this one:

#include <SPI.h>
#include <AD9954.h>
#include <LockFreq.h>

AD9954 DDS(SS_Pin, Reset_pin, update_pin, PS0, PS1, OSK); // whatever pins you're using for these functions...

// declare the Lock object.
// POT_Pin: Analog input pin with the voltage you want to track.
// "Resolution" and "Multiplier" are used to calibrate the sensitivity of the ADC voltage, along with the channel spacing.
// The Arduino Due has a 12-bit ADC -> digital voltage values between 0 and 4095.
// A resolution of 3, for example, means that the ADC must change by 3 for the LockFreq class to recognize a new setpoint.
// the multiplier currently specifies a bitshift on the ADC value to calculate the frequency. So, for example, the Due reads
// a digital voltage value of 300, and the multiplier is 6 -- then, the calculated frequency would be 300*2^6 = 19.2 MHz.
// The channel spacing, then, is given by
// channel spacing = (resolution)*2^(multiplier)
// I'm thinking about changing this so the multiplier is literally a multiplicative factor (rather than bit-shift value),
// although originally I did it this way thinking "bit shift must be faster than multiplication" -- we're using this
// in a (admittedly slow) lock scheme, but I didn't want to do anything that might constrain the bandwidth.

LockFreq Lock(POT_Pin, resolution, multiplier);

void setup(){
    SPI.begin();
    SPI.setClockDivider(4);
    SPI.setDataMode(SPI_MODE0);

    Lock.initialize(DDS, baseFrequency, initialFrequency); // initialize the lock with a particular base frequency
                                                           // (meaning the voltage will shift from this base freq.)
                                                           // an initial frequency of 0 will force LockFreq to poll the
                                                           // POT for an initial voltage value. Otherwise, it will only poll
                                                           // the POT when you call Lock.updateFreq().

}


void loop(){
    Lock.updateFreq(); // update the frequency on the DDS by polling the POT for a new voltage.
}

Implemented features

In addition to the features shown above, you can also update the baseFreq:

LockFreq::updateBaseFreq(unsigned long baseFreq); // updates the base frequency.

If you would instead like to specify a "center" frequency (ie, the frequency output when the Arduino reads a digital voltage value of 2048, AKA 1.65V) so your LockFreq is symmetric about this frequency, you do so with

LockFreq::updateCenterFreq(unsigned long centerFreq);

You can also get the current setpoint with

LockFreq::getSetpoint(); // returns the current voltage setpoint. to get the current *frequency*,
                        // use DDS.getFreq();